Change search
Refine search result
1234 101 - 150 of 159
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 101.
    Olsson, Johan
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Synthesis of Bacterial Oligosaccharides from N. meningitidis and Mechanistic Details of Stereoselective Glycosylations Using a Novel Bicyclic Donor2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis includes two parts. The first part, comprising Chapters 3, 4 and 5, describes the synthesis of bacterial oligosaccharides. In Chapters 3 and 4, the synthesis of branched and phosphorylated oligosaccharide structures corresponding to inner core epitopes of the lipopolysaccharide (LPS) of the Gram-negative bacteria N. meningitidis are discussed. A series of different spacer-equipped, phosphorylated and non-phosphorylated, glycosides has been synthesized as a part of a program involving development of a glycoconjugate-based vaccine against meningitis. Chapter 5 describes the synthesis of a tetrasaccharide corresponding to the repeating unit of the extracellular capsular polysaccharide (CPS) found in S. enteritidis. A short and efficient synthetic route to a trisaccharide acceptor corresponding to the common Gal-Man-Rha backbone found in several Salmonella O-antigen is presented. Further more, the synthesis of a novel tyveloside thioglycoside and the final glycosylation to assemble the complete target tetrasaccharide is reported.

    The second part, Chapters 6 and 7, describes the development of a novel type of glycosyl donor, a 2N,3O-oxazolidinone protected bicyclic thioglycoside. This donor can be used in stereoselective glycosylations where, by tuning the reaction conditions, either complete α- or β-selectivity can be obtained from the same donor/acceptor system. A mechanistic explanation for this behaviour, involving initial formation of the β-anomer followed by a AgOTf-catalyzed in situ endocyclic anomerization to yield the more stable corresponding α-anomer, has been established. The suggested mechanism was supported by a series of NMR-experiments. Finally, in Chapter 7, the synthesis and use of a galacto-configured 2N,3O-oxazolidinone donor for the synthesis of a serine 2-acetamido 2-deoxy galactoside, a versatile building block for the synthesis of mucin O-glycan core structures, is discussed.

  • 102.
    Olsson, Ulrika
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Structural Studies of O-antigen polysaccharides, Synthesis of 13C-labelled Oligosaccharides and Conformational Analysis thereof, using NMR Spectroscopy2008Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In order to understand biological processes, to treat and diagnose diseases, find appropriate vaccines and to prevent the outbreak of epidemics, it is essential to obtain more knowledge about carbohydrate structures. This thesis deals with structure and conformation of carbohydrates, analysed by NMR spectroscopy and MD simulations.In the first two papers, the structures of O-antigen polysaccharides (PS) from two different E. coli bacteria were determined using NMR spectroscopy. The O-antigenic PS from E. coli O152 (paper I) consists of branched pentasaccharide repeating units, built up of three different carbohydrate residues and a phosphodiester, whilst the repeating unit of the O-antigen from E. coli O176 (paper II) is built up of a linear tetrasaccharide consisting of two different monosaccharides.

    In papers III and IV, the conformational analysis of different disaccharides is described. Conformational analysis was performed using NMR spectroscopy and MD simulations (paper IV). In paper III four different glucobiosides were studied using coupling constants and Karplus-type relationships. By use of specific 13C isotopically labelled derivatives, additional coupling constants were obtained and the number of possible torsion angles was reduced by half. In paper IV, we examine the conformations of two disaccharides that are part of an epitope of malignant cells. From NOE and T-ROE experiments, short proton-proton distances around the glycosidic linkage were estimated. Furthermore, interpretation of the extracted coupling constants using Kaplus relationships gave the values of the torsion angles. As in paper III, isotopically labelled compounds were synthesised in order to enhance the sensitivity of the analysis. Finally, MD simulations were performed and the results were compared with results from NMR data.

  • 103.
    Olsson, Vilhelm
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Development of New Synthetic Routes to Organoboronates by Catalytic Allylic Substitution and C-H bond Functionalization2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis describes the development of new catalytic methods for the synthesis and application of organometallic reagents, mainly focusing on allylboronic acid derivatives. Thus, palladium pincer-complex catalysis has been applied for extending the scope of palladiumcatalyzed borylation reactions in the synthesis of regio- and stereodefined functionalized allylboronic acid derivatives. These novel allylboronic acids were also employed as substrates in palladium catalyzed regioselective coupling reactions with iodobenzenes. We have also developed a new one-pot sequence based on preparation of allyl- and vinylboronates

    via catalytic carbon-hydrogen bond activation/borylation reactions. The synthetic scope of the reaction as well as mechanistic studies on the borylation process are presented. Finally, the synthesis of new chiral palladium pincer-complexes is described. These species were employed as catalysts in asymmetric electrophilic allyation of imines.

  • 104.
    Pascanu, Vlad
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Catalytic Processes Mediated by Metal−Organic Frameworks: Reactivity and Mechanistic Studies2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The present thesis describes the development of heterogeneous catalytic methodologies using metal−organic frameworks (MOFs) as porous matrices for supporting transition metal catalysts. A wide spectrum of chemical reactions is covered. Following the introductory section (Chapter 1), the results are divided between one descriptive part (Chapter 2) and four experimental parts (Chapters 3–6).

    Chapter 2 provides a detailed account of MOFs and their role in heterogeneous catalysis. Specific synthesis methods and characterization techniques that may be unfamiliar to organic chemists are illustrated based on examples from this work.

    Pd-catalyzed heterogeneous C−C coupling and C−H functionalization reactions are studied in Chapter 3, with focus on their practical utility. A vast functional group tolerance is reported, allowing access to substrates of relevance for the pharmaceutical industry. Issues concerning the recyclability of MOF-supported catalysts, leaching and operation under continuous flow are discussed in detail.

    The following chapter explores puzzling questions regarding the nature of the catalytically active species and the pathways of deactivation for Pd@MOF catalysts. These questions are addressed through detailed mechanistic investigations which include in situ XRD and XAS data acquisition. For this purpose a custom reaction cell is also described in Chapter 4.

    The scope of Pd@MOF-catalyzed reactions is expanded in Chapter 5. A strategy for boosting the thermal and chemical robustness of MOF crystals is presented. Pd@MOF catalysts are coated with a protecting SiO2 layer, which improves their mechanical properties without impeding diffusion. The resulting nanocomposite is better suited to withstand the harsh conditions of aerobic oxidation reactions. In this chapter, the influence of the nanoparticles’ geometry over the catalyst’s selectivity is also investigated.

    While Chapters 3–5 dealt with Pd-catalyzed processes, Chapter 6 introduces hybrid materials based on first-row transition metals. Their reactivity is explored towards light-driven water splitting. The heterogenization process leads to stabilized active sites, facilitating the spectroscopic probing of intermediates in the catalytic cycle.

  • 105.
    Pathi Pati, Stalin Reddy
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Development of new Catalytic Methods for the Selective Synthesis of Heterocycles2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In the field of organic chemistry, the development of new catalytic methods for the synthesis of complex molecules from simple precursors is a top priority. The main focus of this thesis concerns the diastereoselective synthesis of heterocyclic compounds using main group elements as Lewis acid catalysts.

    The first part of this thesis deals with an annulation reaction of nitrones with oxiranes, aziridines, and thiiranes using Al(III) or In(III) catalysts. From this protocol, 1,4,2-dioxazinanes, 1,2,4-oxadiazinanes, and 1,4,2-oxathiazinanes were obtained in moderate to high yields with excellent diastereoselectivity. The transformation was found to be stereospecific and proceed via an SN2-mechanism.

    The second and third parts concern the development of In(III)-catalyzed annulation of carbonyl compounds, amines, and alkynyl enones. InBr3 was found to be an efficient catalyst for the activation of alkynyl enones in a multicomponent reaction with aldehydes and amines. The method affords cyclopenta[c]furans in high yields and in good to excellent diastereomeric ratios. Bicyclo[3.n.1]alkenone derivatives were formed via a double Michael addition reaction of cyclic ketones, amines, and alkynyl enones, in the presence of InCl3. The utility of these protocols was also demonstrated by sequential transformations.

    In the fourth part, AgOTf and CuI were found to be efficient catalysts for the activation of pyridine-substituted enynes towards enamines, providing indolizine derivatives in high yield and good diastereomeric ratios.

    In the last part of the thesis, 1,2-aminoarylation of γ,δ-unsaturated oxime esters with arylboronic acids using Ni catalysis is discussed. The protocol demonstrates the potential of Ni-catalysts for the generation of iminyl radicals to furnish functionalized pyrroline derivatives. The utility of this protocol was exemplified by transforming the pyrroline products to the corresponding pyrrole and pyrrolidine derivatives. 

  • 106.
    Pendrill, Robert
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Conformations of Flexible Oligosaccharides: Molecular Simulations and NMR spectroscopy2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The conformational preferences of several oligosaccharides are investigated herein using a combination of NMR spectroscopy and molecular dynamics (MD) simulations, focusing on the torsion angles associated with the glycosidic linkages.

    Strategies for obtaining usable J-HMBC spectra for carbons with an adjacent 13C label are described. By employing a selective pulse or a constant time modification, spectra free from interferences are obtained for site-specifically 13C labeled oligosaccharides.

    Intermolecular hydrogen bonding in sucrose is investigated using MD simulations performed at different concentrations. One of the most frequent intermolecular hydrogen bonds in the simulations, O3f∙∙∙HO3g, was detected using the HSQC-TOCSY NMR experiment.

    Based on MD simulations and NMR spectroscopy, the conformational ensemble for a trisaccharide segment of the LeaLex hexasaccharide is proposed to feature conformational exchange between conformations with positive and negative values for the ψ3 torsion angle in the β-D-GlcpNAc-(1→3)-β-D-Galp linkage.

    Using MD simulations, the conformation of the N-acetyl group is shown to influence the glycosidic conformation at a nearby linkage in two oligosaccharides.

    Short (1→6)-linked oligosaccharides are shown to exhibit conformational exchange at the ω and ψ torsion angles. Notably, the former torsion angle populates states with ψ ≈ ±90°. Conformationally sensitive homo- and heteronuclear coupling constants are determined using various NMR experiments. The experimental data, including effective distances from NOESY obtained for two of the compounds, is used to improve the representation of the ω torsion angle in the CHARMM36 force field.

  • 107.
    Persson, Andreas K. Å.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Palladium(II)-Catalyzed Oxidative Cyclization Strategies: Selective Formation of New C-C and C-N Bonds2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The main focus of this thesis has been directed towards preparation and oxidative carbocyclization of en-, dien- and aza-enallenes.

    In the first part of this thesis, a stereoselective oxidative carbocyclization of dienallenes was realized. By employing cheap and readily available palladium trifluoroacetate we were able to efficiently cyclize a variety of dienallenes into hydroxylated carbocycles in high yield and high selectivity. This oxidative process was compatible with two different reoxidation protocols: one relying on p-benzoquinone (BQ) as the oxidant and the other employing molecular oxygen as the oxidant.

    In the second part of the thesis the carbocyclization methodology was extended to include carbocyclization of aza-enallenes. This was achieved in two distinct steps. First, a copper-catalyzed coupling of allylic sulfonamides with bromoallenes was developed, giving access to the corresponding aza-enallenes. Subjecting these substrates to catalytic amounts of palladium acetate, along with BQ as the oxidant, rendered N-heterocycles in good yield. The reactivity of these N-heterocycles towards activated dienophiles was later exploited in a tandem (aerobic) oxidative carbocyclization/Diels-Alder reaction.

    The third topic involves efficient oxidative arylative/borylative carbocyclization of enallenes. These reactions, catalyzed by palladium acetate, relies on transmetallation of a (σ-alkyl)palladium(II) intermediate with diboranes or arylboronic acids. With this novel methodology we were able to obtain an array of arylated or borylated carbocycles, as single diastereomers, in high yield.

    Finally, we developed a palladium(II)-catalyzed cyclization of allylic carbamates. This mild, operationally simple, and scalable catalytic reaction opens up access to an array of oxazolidinones in high yield and excellent diastereoselectivity.

  • 108.
    Peters, Byron
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Iridium Catalysed Asymmetric Hydrogenation of Olefins and Isomerisation of Allylic Alcohols2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The work described in this thesis is focused on exploring the efficacy of asymmetric iridium catalysis in the hydrogenation of challenging substrates, including precursors to chiral sulfones and chiral cyclohexanes. Furthermore, iridium catalysis was used to isomerise allylic alcohols to aldehydes, and in a formal total synthesis of Aliskiren (a renin inhibitor). A large variety of unsaturated sulfones (cyclic, acyclic, vinylic, allylic and homoallylic) were prepared and screened in the iridium catalysed hydrogenation reaction using a series of previously developed N,P-ligated Ir-catalysts. The outcome was a highly enantioselective (>90% ee) protocol to prepare sulfones bearing chiral carbon scaffolds, sometimes having purely aliphatic substituents at the stereogenic centre. Furthermore, performing the Ramberg-Bäcklund reaction on the chiral products, under optimised conditions, produced cyclic and acyclic unsaturated derivatives without erosion of enantiomeric excess. This hydrogenation protocol was also successful in the hydrogenation of a number of cyclohexene-containing compounds. Minimally functionalised, functionalised and heterocycle-containing cyclohexenes were hydrogenated in up to 99% ee. Hitherto, both chiral sulfones and chiral cyclohexanes have been challenging targets for most catalytic asymmetric methodologies. Although the preparation of aldehydes and ketones by isomerisation of the corresponding allylic alcohol is well established, there has been limited success in the development of good enantioselective protocols. For the isomerisation of a number γ,γ-allylic alcohols to the corresponding chiral aldehydes, high enantioselectivities (up to >99% ee) and modest yields were achieved using an N,P-iridium catalyst. Noteworthy is the high selectivity obtained for isomerisation of and dialkyl γ,γ-allylic alcohols, which prior to this study had been difficult to isomerise in high enantioselectivity. Preparation of a key intermediate used in the synthesis of Aliskiren, a renin inhibitor drug was also accomplished. Using a convergent synthesis strategy, two allylic alcohol fragments were hydrogenated with high enantiomeric excess (>92% ee). These fragments were then joined using a Julia-Kocienski reaction, providing >95% geometry around the C=C bond, which was crucial for the subsequent steps in the synthesis.

  • 109.
    Pu, Maoping
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Molecular Motion in Frustrated Lewis Pair Chemistry: insights from modelling2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Mechanisms of reactions of the frustrated Lewis pairs (FLPs) with carbon dioxide (CO2) and hydrogen (H2) are studied by using quantum chemical modelling. FLPs are relatively novel chemical systems in which steric effects prevent a Lewis base (LB) from donating its electron pair to a Lewis acid (LA). From the main group of the periodic table, a variety of the electron pair donors and acceptors can create an FLP and the scope of the FLP chemistry is rapidly expanding at present. Representative intermolecular FLPs are phosphines and boranes with bulky electron-donating groups on phosphorus and bulky electron-withdrawing groups on boron – e.g., the tBu3P/B(C6F5)3 pair. The intramolecular FLPs feature linked LB and LA centers in one molecule.

    Investigations of the FLP reaction mechanisms were carried out using the transition state (TS) and the potential energy surface (PES) calculations plus the Born-Oppenheimer molecular dynamics (BOMD) as an efficient and robust implementation of general ab initio molecular dynamics scheme. In BOMD simulations, quantum and classical mechanics are combined. The electronic structure calculations are fully quantum via the density functional theory (DFT). Molecular motion at finite (non-zero) temperature is explicitly accounted for at non-quantized level via Newton’s equations. Due to recent advancements of computers and algorithms, one can treat fairly large macromolecular systems with BOMD and even include significant portion of the first solvation shell surrounding a large reacting complex in the molecular model.

    Main results are as follows. It is shown that dynamics is significant for understanding of FLP chemistry. The multiscale nature of motion – i.e., light molecules such as CO2 or H2 versus a pair of heavy LB and LA molecules – affects the evolution of interactions in the reacting complex. Motion which is perpendicular to the reaction coordinate was found to play a role in the transit of the activated complex through the TS-region. Regarding the heterolytic cleavage of H2 by tBu3P/B(C6F5)3 FLP simulated in gas phase and with explicit solvent, it was found that (i) the reaction path includes shallow quasi-minima “imbedded” in the TS-region, and (ii) tBu3P/B(C6F5)3 are almost stationary while proton- and hydride-like fragments of H2 move toward phosphorous and boron respectively. For binding of CO2 by tBu3P/B(C6F5)3 FLP, it was found that (i) the reacting complex can “wander” along the “potential energy wall” that temporarily blocks the path to the product, and (ii) the mechanism can combine the concerted and two-step reaction paths in solution. The discovered two-step binding of CO2 by tBu3P/B(C6F5)3 FLP involves solvent-stabilized phosphorus-carbon interactions (dative bonding). These and other presented results are corroborated and explained using TS and PES calculations. With computations of observable characteristics of reactions, it is pointed out how it could be possible to attain experimental proof of the results.

  • 110.
    Quan, Xu
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Hydrogenation, Transfer Hydrogenation and Hydrogen Transfer Reactions Catalyzed by Iridium Complexes2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The work described in this thesis is focused on the development of new bidentate iridium complexes and their applications in the asymmetric reduction of olefins, ketones and imines. Three new types of iridium complexes were synthesized, which included pyridine derived chiral N,P-iridium complexes, achiral NHC complexes and chiral NHC-phosphine complexes. A study of their catalytic applications demonstrated a high efficiency of the N,P-iridium complexes for asymmetric hydrogenation of olefins, with good enantioselectivity. The carbene complexes were found to be very efficient hydrogen transfer mediators capable of abstracting hydrogen from alcohols and subsequently transfer it to other unsaturated bonds. This hydrogen transferring property of the carbene complexes was used in the development of C–C and C–N bond formation reactions via the hydrogen borrowing process. The complexes displayed high catalytic reactivity using 0.5–1.0 mol% of the catalyst and mild reaction conditions. Finally chiral carbene complexes were found to be activated by hydrogen gas. Their corresponding iridium hydride species were able to reduce ketones and imines with high efficiency and enantioselectivity without any additives, base or acid.

  • 111.
    Rabten, Wangchuk
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    The Use of N,P-Iridium and N,P-Palladium Complexes in Asymmetric Synthesis2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The work presented in this thesis concerns asymmetric catalysis using chiral N,P-ligands and iridium or palladium transition metals. The first part  (Chapters 2 and 3) highlights the N,P-iridium catalyzed asymmetric hydrogenation of 1,4-cyclohexadienes having functionalized or unfunctionalized substituents, including allylsilane side chains. A series of N,P-iridium catalysts were synthesized and screened on a number of cyclohexadienes. The developed N,P-iridium catalysts have provided excellent chemo-, regio- and enantioselectivity for most of the products obtained. For substrates having an allylsilane sidechain, the chiral cyclic allylsilane products were used to induce stereocontrol in a subsequent Hosomi-Sakurai reaction using TiCl4 as Lewis acid and aldehydes as electrophiles. The corresponding homoallylic alcohols were obtained in good to excellent diastereoselectivity. 

    The second part (Chapter 4) describes the N,P-iridium catalyzed asymmetric hydrogenation of various vinyl fluorides. A number of tri- and tetrasubstituted vinyl fluorides were synthesized and evaluated for the asymmetric hydrogenation. The corresponding saturated chiral fluoro compounds were obtained in very high enantioselectivity (up to 99% ee). The defluorination, usually known to occur under the catalytic hydrogenation conditions, were not observed for the majority of the substrates. 

    Finally, Chapter 5 describes the application of N,P-ligands in the asymmetric cycloisomerization of 1,6-enynes using a palladium precatalyst. The enantioselectivities for the products were found to depend both on the substrate as well as the hydrogen source. These developed catalytic reactions provide attractive methods to create multiple stereogenic centers in a molecule in relatively few steps from readily available starting materials.

  • 112.
    Ramstadius, Clinton
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Synthesis of Carbohydrate Mimics and Development of a Carbohydrate Epimerisation Method2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis the synthesis of several hydrolytically stable carbohydrate mimics with the potential to function as glycosidase or lectin inhibitors are described. This work is presented in Chapters 2-5.

    Chapters 2 and 3 describe synthetic efforts for producing carbasugars, and include the first synthesis of 1,2-bis-epi-valienamine and the preparation of two previously known aminocarbasugars. All three compounds were synthesised starting from D-mannose, using ring-closing metathesis as the key step. 1,2-Bis-epi-valienamine was found to inhibit Cellulomonas fimi β-mannosidase with a Ki value of 140 mM. Also included is the development of a novel synthetic route from cheap D-fructose to three mannose-mimicking carbasugars using a ring-closing metathesis strategy. Two of the compounds are potential inhibitors of the FimH adhesin.

    In Chapters 4 and 5 the synthesis of a number of pseudodisaccharides are presented; valienamine- and epi-valienamine-containing pseudodisaccharides and a small library of S-linked pseudodisaccharides were prepared. Various synthetic strategies were explored, including an alkylation strategy, Mitsunobu couplings, and sulfonate displacements. This is the first report on the synthesis of a valienamine pseudodisaccharide with β-lyxo-configuration. Two of the S-linked pseudodisaccharides were found to bind to Concanavalin A with high affinity.

    The final chapter (Chapter 6) of this thesis focuses on the development of a carbohydrate epimerisation method using transition metal catalysis. Two equilibrium constants involving gluco/manno- and gluco/allo-alcohols were determined via this method.

  • 113.
    Reitti, Marcus
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Diaryliodonium Salts: Synthesis, Applications and Computational Investigations2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Organic chemists have the ability to create complex organic molecules by connecting molecular building blocks in different ways. To name a few, these molecules are used as medicines, pesticides or in our household electronics, and are therefore crucial to life as we know it. While many excellent methods for the connection of these fragments are known, serious issues regarding efficiency and sustainability remain. Our research concerns the use of diaryliodonium salts as a way of improving on these issues. Diaryliodonium salts are hypervalent iodine reagents used to transfer aryl groups to suitable nucleophiles. This thesis concerns the synthesis of these reagents and their use in the formation of carbon-nitrogen and carbon-oxygen bonds.

    The first project investigates the possibility to synthesize unsymmetrical diaryliodonium salts starting from elemental iodine and arenes, as such a method could be more cost efficient and sustainable compared to existing methods starting from iodoarenes. It was found that highly sterically congested diaryliodonium salts could be synthesized in high yields.

    Next, we applied diaryliodonium salts in the arylation of nitrite to form aromatic nitro compounds. The methodology offered a broad scope with good to excellent yields. Furthermore, we presented the in situ functionalization of diaryliodonium salts that had been formed from iodoarenes and arenes. This conceptually novel approach could be a step towards a catalytic reaction using diaryliodonium salts.

    In the third project we investigated the mechanisms of O-arylations with diaryliodonium salts to provide a deeper understanding of the reaction pathways involved in product and byproduct formation. Reactions between electron-rich diaryliodonium salts, hydroxides or secondary alcohols were studied.  When using hydroxide as the nucleophile, the side products could be suppressed by the addition of aryne traps, suggesting such an intermediate in the reaction. A novel mechanism for the formation of the aryne was proposed based on DFT calculations.  When alcohols were used we detected the oxidation of the alcohol rather than aryne products. The oxidized product was shown to not originate from arynes or a radical process but was formed via an intramolecular deprotonation from a 4-coordinated intermediate as suggested by DFT-calculations and experiments.

    In the final project we developed two complementary methods for the synthesis of phenols using hydroxide surrogates as nucleophiles. These compounds have previously been difficult to make using diaryliodonium salts due to aryne formation or overarylation to form diaryl ethers. The first method used hydrogen peroxide as the surrogate and allowed formation of electron-deficient and moderately electron-rich phenols. The synthesis of ortho-alkyl substituted phenols could be accomplished by using silanols as the surrogate. This allowed us to synthesize several highly congested phenols in good yields. Highly electron-rich diaryliodonium salts were, however, not compatible with either of the two methods.

  • 114.
    Ritzén, Helena
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Syntheses of naturally occurring fatty acid esters of sucrose and heptose-containing oligosaccharides found in the Salmonella Ra core1992Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Nine sucrose esters, acylated in the glucopyranosyl moiety, have been synthesized from the same precursor, 3-0-allyl-3',4',6'-tri-0-benzyl-4,6-0- (4-metoxybenzylidene)sucrose. The sucrose esters synthesized include the major compounds found in tobacco and potato plants, i. e., 6-0-acetyl-2,3,4- tri-0-[3-(S)-methylpentanoyl]sucrose and 2,3-di-0-isobutyryl-6-0- decanoylsucrose.

    Synthesis of the trisaccharide 2-(4-trifluoracetamidophenyl)ethyl 0-(Lglycero- a-D-manno-heptopyTanosyl)-(l->7)-0-(L-glycero-a-D-mannoheptopyranosyl)-( l -»3)-L-g/ycero-a-D-/nanno-heptopyranoside is described. While still protected, this oligosaccharide is suitable for further reactions. Using this strategy, a tetra-, a penta- and a hexasaccharide, all containing the same triheptoside, were synthesized. All oligosaccharides correspond to stmctures found in the Salmonella Ra core.

  • 115.
    Ruda, Katinka
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Synthesis of inositol phosphoglycans and analogues thereof1998Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis describes the synthesis of inositol phosphoglycans (IPG) corresponding to glycosyl-phosphatidylinositol (GPI) anchors found on the cell surface of the parasite Leishmania. Synthesis of an IPG which is a putative second messenger for insulin, and of analogues thereof is also discussed.

    The IPG structures synthesized contain mono-, tri-, and hexasaccharides linked to an inositol phosphate. Analogues of the putative second messenger contain glucosamine, instead of myo-inositol phosphate, coupled to either phosphorylated D-mannose or phosphorylated L-fucose. The synthetic work involved the development of procedures for obtaining optically pure myo-inositol-glucosamine derivatives, the formation of phosphomono- and diesters (both cyclic and acyclic) and oligosaccharide synthesis.

  • 116.
    Rydner, Lina
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Development of strategies for construction of thioglycoside building blocks corresponding to repeating triads of Cryptococcus neoformans GXM capsular polysaccharide2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis focuses on the development of methods for synthesis of thioglycoside building blocks corresponding to the repeating units of the capsular polysaccharide (CPS) of Cryptococcus neoformans, an opportunistic fungal pathogen. The building blocks are suitable for construction of large synthetic oligosaccharides related to the native CPS-structures which are to be used in biological studies in order to identify protective epitopes with the aim to develop a glycoconjugate vaccine against C. neoformans infections.

    Chapter 3 describes the improved synthesis of di- and trisaccharide glucuronic acid-containing thioglycoside blocks by introduction of the carboxylic acid motif at the di- and trisaccharide level through oxidation of a glucose residue. The new approach requires a number of extra steps, but has proven to be more reliable and more easily reproducible since problems encountered in glycosylations with glucuronic acid donors and benzylation of glucuronic acid-containing derivatives are circumvented.

    In Chapter 4 the development of a synthetic route to xylose-substituted tri- and tetrasaccharide building blocks where the protecting group strategy allows for orthogonal glycosylations with thioglycoside acceptors is discussed.

    Chapter 5 describes the synthetic pathway to the glucuronic acid-containing derivatives according to the methodology developed in Chapter 4 and the assembly of a hexasaccharide building block corresponding to the repeating triad of serotype A.

    In Appendix І an alternative strategy for synthesis of glucuronic acid-substituted derivatives by direct introduction of a perbenzylated glucuronic acid trichloroacetimidate donor where stereoselectivity is achieved through the use of an 1,6-anhydro acceptor.

  • 117.
    Rönnols, Jerk
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Structure, dynamics and reactivity of carbohydrates: NMR spectroscopic studies2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The main focus of this thesis is on the ring conformations of carbohydrate molecules; how the conformational equilibria and the rates of the associated interconversions are affected by the molecular constitution and their surroundings.

    The conformational equilibria of a group of amine linked pseudodisaccharides, designed as potential glycosidase inhibitors, comprising α-D-altrosides are described in Chapter 3. The OS2 conformation was largely populated, and the ring conformation was found to depend on the charge of the amine functionality.

    The conformations of β-D-xylopyranoside derivatives with naphthyl-based aglycones, which are potential anti-cancer agents, are described in chapter 4. Solvent dependent flexibility was observed. Intramolecular hydrogen bonds were concluded to be involved in the stabilization of 1C4 conformers in non-hydrogen bonding solvents of low polarity.

    Chapter 5 describes the first measurements of the conformational exchange rates of mannuronic acid ester derivatives between the 4C1 and 1C4 conformations, through DNMR measurements. The relative reactivity of glycosyl triflates as electrophiles in glycosylation reactions were investigated with NMR-based competition experiments.

    In Chapter 6, investigations of ruthenium-catalyzed epimerizations of the allylic alcohols of glycal derivatives, and stereoselective synthesis of esters through a DYKAT protocol, are described. The kinetics of the epimerizations were elaborated through different NMR-spectroscopic methods.

    Chapter 7 describes additions of NMR chemical shift data of mono- and oligosaccharides to database of the computer program CASPER, and applications thereof.

  • 118.
    Samec, Joseph S M
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Ruthenium-catalyzed hydrogen transfer involving amines and imines: Mechanistic studies and synthetic applications2005Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis deals with ruthenium-catalyzed hydrogen transfer involving amines and imines and is divided into two parts.

    In Part 1 a mechanistic study has been performed. The complexation of the imine to the catalyst and the decomplexation patterns of the formed ruthenium-amine complexes, isotope studies, and exchange studies show that the mechanism of the hydrogen transfer involving amines and imines is different from the hydrogen transfer involving alcohols and carbonyls.

    In Part 2 synthetic applications of the hydrogen transfer is presented. First the rutheniumcatalyzed transfer hydrogenation of imines by 2-propanol in an unpolar solvent was investigated. The corresponding amines were isolated in good to excellent yields. Even imines bearing labile functional groups were smoothly transferred to amines with very low catalyst loadings and short reaction times employing microwave heating. Then the reverse reaction, transfer dehydrogenation of amines to imines, was investigated using either MnO2 or oxygen as terminal oxidant. Important products such as aldimines, ketimines, and non benzylic anilines were prepared in the aerobic oxidation. We also demonstrated that the aerobic oxidation is compatible with proline-mediated organocatalysis, yielding amines in high yields and ee:s. Finally the racemization of chiral amines was investigated. A cumbersome side product formation was investigated and hampered by the use of a mild hydrogen donor, giving a mild and efficient racemization process for both primary and secondary amines.

  • 119.
    Sandström, Anders G.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Protein Engineering of Candida antarctica Lipase A: Enhancing Enzyme Properties by Evolutionary and Semi-Rational Methods2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Enzymes are gaining increasing importance as catalysts for selective transformations in organic synthetic chemistry. The engineering and design of enzymes is a developing, growing research field that is employed in biocatalysis. In the present thesis, combinatorial protein engineering methods are applied for the development of Candida antarctica lipase A (CALA) variants with broader substrate scope and increased enantioselectivity. Initially, the structure of CALA was deduced by manual modelling and later the structure was established by X-ray crystallography. The elucidation of the structure of CALA revealed several biocatalytically interesting features. With the knowledge derived from the enzyme structure, enzyme variants were produced via iterative saturation mutagenesis (ISM), a powerful protein engineering approach. Several of these variants were highly active and enantioselective towards bulky esters. Furthermore, an extensively combinatorial protein engineering approach was developed and investigated. A CALA variant with a spacious substrate binding pocket that can accommodate an unusually bulky substrate, an ester derivate of the non-steroidal anti-inflammatory drug (S)-ibuprofen, was obtained with this approach.

  • 120.
    Segerstedt, Eva
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Approaches to the synthesis of candidate glycoconjugate vaccines against non-typeable Haemophilus influenzae2003Doctoral thesis, comprehensive summary (Other academic)
  • 121.
    Selander, Nicklas
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Catalytic Functionalization of Allylic Substrates by Palladium Pincer Complexes2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis is based on the development of novel catalytic reactions for the synthesis and application of organometallic reagents. The main focus is directed towards organoboronate derivatives. We developed an efficient procedure for converting allylic alcohols to the corresponding allylboronates using palladium pincer complexes as catalysts. The reactions were performed under mild conditions with high selectivity, allowing further one-pot transformations. Using this approach, a variety of stereodefined homoallylic alcohols and amino acid derivatives were synthesized via trapping of the in situ generated allylboronate derivatives with an appropriate electrophile. The synthetic scope of these types of multi-component reactions is broad as many different substrate allylic alcohols may be used together with various electrophiles. Several aspects of these reactions were studied, including different reagents, catalysts and electrophiles.

    Furthermore, we studied the possibility to use oxidizing reagents as an essential component in the functionalization of olefins. Two main strategies were utilized for these catalytic methods using palladium pincer complexes. The functional group was either transferred from the oxidizing reagent, or introduced via an oxidation-transmetallation route. We propose that both methods involve palladium(IV) intermediates thus expanding both the coordination sphere of palladium and the synthetic scope of pincer complex catalysis.

  • 122.
    Shatskiy, Andrey
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Ru-Based Water Oxidation Catalysts: Development and Mechanistic Studies2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Oxidation of water constitutes one of the most challenging processes in artificial photosynthesis, which aims at storing solar energy in the form of chemical bonds of high-energy fuels. To facilitate this process, efficient and durable water oxidation catalysts have to be developed and integrated into the complete photosynthetic cells. Importantly, the intricate complexity of such devices requires the catalyst not only to be highly efficient and robust, but also operate through a well-defined mechanism.

    This thesis describes the development and mechanistic studies of new water oxidation catalysts based on ruthenium. The first part of the thesis describes the synthesis of a dinuclear ruthenium-based catalyst active for both chemical and light-driven water oxidation. This catalyst displayed a pronounced influence of the acetonitrile co-solvent on the redox properties, which was studied in detail by electrochemical methods. In the second part, a new benzimidazole-based mononuclear catalyst was evaluated. The activity of the catalyst was studied for chemical and light-driven water oxidation, and insight into the operating mechanism was provided with the help of density functional theory calculations. In the third part of the thesis, a new mononuclear ruthenium-based catalyst was prepared and evaluated for electrochemically-driven water oxidation. This catalyst displayed activity similar to that of the current state-of-the-art water oxidation catalyst, while eliminating its main drawback, that is incomplete activation. The redox properties of the new catalyst were studied in detail by electrochemical and spectroscopic techniques, providing insight into the origins of its improved performance. Finally, in the fourth part of the thesis, a heterogeneous nanoparticulate catalyst immobilized on a solid support is described. The catalyst displayed high activity and stability during chemical and light-driven water oxidation, which was attributed to the small average particle size and efficient anchoring of the catalyst to the heterogeneous support via an oxidatively-stable linker.

  • 123.
    Skantz, Linnéa
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Synthesis of biologically active oligosaccharides of the Lewis b family and investigations towards the synthesis of glycoclusters2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The gastric pathogen Helicobacter pylori is a Gram negative bacterium which may cause diseases such as peptic ulceration and gastric adenocarcinoma. It colonises a host by attaching to the gastric epithelial cells, an attachment mediated by outer membrane proteins on the bacterial surface, e.g, the blood group antigen binding adhesin, BabA. This adhesin recognises and binds to specific carbohydrates, Lewis blood group antigens, on the epithelial cell walls.

    This thesis presents the synthesis of three oligosaccharides of the Lewis family. A new and improved block synthesis of a Leb hexasaccharide and synthesis of HSA-conjugates thereof are described. Also presented are the syntheses of a Leb pentasaccharide and a B-Leb heptasaccharide via linear routes. The latter strategy is designed to enable the synthesis of other Lewis blood group antigens by only minor changes in protection patterns.

    Investigations have been made towards finding a route for the synthesis of glycoclusters using of unprotected carbohydrates. The biologically active dendrimers will be used in examinations of binding to galectin-3, an important animal lectin abundant in nature.

    The thesis also includes an efficient synthesis of an oxazolidinone protected thioethyl LacNAc disaccharide, and its ability as a donor has been examined.

  • 124.
    Slagbrand, Tove
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Development and Applications of Molybdenum-Catalyzed Chemoselective Amide Reduction2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis covers the development of catalytic methodologies for the mild and chemoselective hydrosilylation of amides. The first part describes the investigation of the Mo(CO)6-catalyzed reduction of carboxamides. It was found that the reduction could be controlled by tuning the reaction temperature and either amines or aldehydes could be obtained selectively. The system showed an unprecedented chemoselectivity and the amide reduction could take place in the presence of other reducible functional groups such as ketones, aldehydes, and imines. Moreover, the transformation could be performed on a preparative scale and was further employed in the synthesis of Donepezil, a pharmaceutical drug used in the treatment of Alzheimer´s disease.

    The third chapter concerns the development of the Mo(CO)6-mediated hydrosilylation protocol for the reduction of carboxamides containing acidic α-hydrogens. In this case, enamines were formed and a high level of chemoselectivity was observed. Enamines containing sensitive functional groups such as ketones, aldehydes and imines were generated. The enamines were not isolated but used in subsequent catalytic reductive functionalization of amides, which is described in the last part of the thesis (Chapters 4 – 7). The in situ formed enamines were reacted with a wide variety of electrophiles, generating heterocyclic compounds as triazolines, triazoles, 4,5-dihydroisoxazoles and pyrimidinediones. N-sulfonylformamidines as well as thioacrylamides could also be prepared with this approach. The protocols for the synthesis of triazolines, triazoles and N-sulfonylformamidines could additionally be performed on a preparative scale, showing the practicality of the methodology.

  • 125.
    Slättegård, Rikard
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Synthesis of Structures Related to the Capsular Polysaccharide of Neisseria meningitidis Serogroup A and to Mycothiol2007Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis describes the synthesis of structures related to the capsular polysaccharide of Neisseria meningitidis serogroup A and the synthesis of analogues of mycothiol, a compound produced by Mycobacterium tuberculosis. The first part of the thesis describes the synthesis of structural elements present in the native capsular polysaccharide of Neisseria meningitidis serogroup A. In this part, an improved synthesis of 2-azido-2-deoxy-D-mannopyranose is included. The second part of the thesis describes the formation of stable C-phosphonate analogues related to the capsular polysaccharide. The last part outlines the formation of analogues of mycothiol, where the syntheses of a bicyclic analogue and a thioglycosidic analogue are described.

  • 126.
    Solin, Niclas
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Development of Palladium-Catalyzed Transformations Involving η1-Allypalladium Species2004Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis is focused on investigation of the structure, reactivity and isomerization reactions of η1-allylpalladium complexes, which are key intermediates in catalytic transformations. The first part of this thesis concerns the structure and reactivity of bis-allylpalladium complexes. We have studied the regioselective palladium-catalyzed coupling reaction of various dialkylsubstituted allyl chlorides with allylstannanes and benzylidenemalonitrile, affording functionalized 1,7-octadienes. We have also found that benzylidenemalonitrile can be replaced by isocyanates providing bis-allylated amides. The second part is a computational study on the η3-η1-η3 isomerization of allylpalladium complexes. The mechanism of the isomerization was studied by DFT. It was found that the isomerization involves tetra-coordinated η1-allylpalladium intermediates. Alkyl substitution of the metalated carbon leads to destabilization of the η1-allylpalladium intermediate, which increases the activation energy of the isomerization process. The last part describes our efforts to extend the synthetic scope of mono-allylpalladium chemistry to include catalytic allylation of imine and aldehyde substrates. We have found that this reactivity can be achieved by the use of strongly coordinating tridentate ligands on palladium. The η1-allylpalladium intermediate has been observed by NMR-spectroscopy, and DFT calculations have been performed to show the feasibility of an electrophilic attack occuring on the allyl moiety.

  • 127.
    Stenutz, Roland
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    The structure and conformation of saccharides determined by experiment and simulation1997Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    A computer program, CASPER, for sequence determination of oligosaccharides and regular polysaccharides using NMR-data, has been extended to support multiply branched structures. The program has been modified to allow the use of incomplete experimental data since spectral overlap can be a problem even at high fields. The resulting program was tested and used in the structure determination of the capsular polysaccharide from Klebsiella type K52.

    Four carboxyethyl-substituted sugars, methyl 4-O-[(R)- and (S)-1-carboxyethyl]-a-L-rhamnopyranoside and methyl 6-O-[(R)- and (S)-1-carboxyethyl]-a-D-galactopyranoside have been synthesized. The conformational properties of the latter two have been investigated by both NMR spectroscopy and molecular modelling studies. For the NMR-studies stereospecifically deuterated compounds were prepared.

  • 128.
    Stridfeldt, Elin
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Hypervalent Iodine Reagents in Metal-Free Arylations and Vinylations: Investigation of Suitable Coupling Partners and Synthesis of New Reagents2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis concerns the development of metal-free reactions to obtain carbon-heteroatom and carbon-carbon bonds. This is achieved by transferring carbon ligands from hypervalent iodine reagents to suitable nucleophiles.

    The bulk of the work presented herein concerns arylation of oxygen and nitrogen nucleophiles, using the well-known diaryliodonium salts as aryl sources. In the first project, O-arylation of the oxime ethyl acetohydroxamate was studied. It was found that electron-poor as well as electron-rich aryl moieties could be transferred successfully to this nucleophile. Furthermore, the protocol could be extended to a sequential one-pot synthesis of benzo[b]furans. This method allowed for a fast synthesis of the natural product stemofuran A and formal syntheses of other natural products.

    In a successive project, O-arylation of hydroxide and aliphatic alkoxides was investigated. It is known that electron-poor aryl moieties can be transferred to these nucleophiles in moderate to high yields. However, combined with more electron-rich diaryliodonium salts, a large amount of side products were formed. These were suppressed upon addition of aryne traps, suggesting that aryne pathways are competing with the desired ligand coupling. It was also observed that secondary alcohols were oxidized to the corresponding ketones. The mechanism for this oxidation was investigated and aryne pathways could be excluded. Instead we suggest that the carbinol hydrogen gets deprotonated via an internal mechanism, after the alkoxide has coordinated to the iodonium salt. Highly sterically congested alkyl aryl ethers could be obtained in high yields by combining tertiary alcohols with ortho-blocked diaryliodonium salts. 

    Next, N-arylation of secondary acyclic amides was studied using acetanilide as the model substrate. This procedure was suitable for transfer of electron-poor as well as ortho-substituted aryl moieties, but attempts to transfer very electron-rich aryl groups were unsuccessful. On the other hand, the amides displayed a complementary reactivity, allowing phenylation of electron-rich amides. 

    In the final project, a one-pot synthesis of the cyclic iodonium reagent vinylbenziodoxolone is presented. These compounds have not been explored as reagents earlier. Initial screenings showed that the vinyl moiety could be transferred to nitrocyclohexane with opposite regioselectivity compared to the acyclic analogue of the reagent.

  • 129.
    Ståhle, Jonas
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Structure Elucidations of Bacterial Polysaccharides using NMR Spectroscopy and Bioinformatics2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Carbohydrates are ubiquitous components in nature involved in a range of tasks. They cover every cell and contribute both structural stability as well as identity. Lipopolysaccharides are the outermost exposed part of the bacterial cell wall and the primary target for host-pathogen recognition. Understanding the structure and biosynthesis of these polysaccharides is crucial to combat disease and develop new medicine. Structural determinations can be carried out using NMR spectroscopy, a powerful tool giving information on an atomistic scale. This thesis is focused on method development to study polysaccharide structures as well as application on bacterial lipopolysaccharides. The focus has been to incorporate a bioinformatics approach prior to analysis by NMR spectroscopy, and then computer assisted methods to aid in the subsequent analysis of the spectra.

    The third chapter deals with the recent developments of ECODAB, a tool that can help predict structural fragments in Escherichia coli O-antigens. It was migrated to a relational database and the aforementioned predictions can now be made automatically by ECODAB. The fourth chapter gives insight into the program CASPER, a computer program that helps with structure determination of oligo- and polysaccharides. An approach to determine substituent positions in polysaccharides was investigated. The underlying database was also expanded and the improved capabilities were demonstrated by determining O-antigenic structures that could not previously be solved. The fifth chapter is an application to O‑antigen structures of E. coli strains. This is done by a combination of NMR spectroscopy and bioinformatics to predict components as well as linkages prior to spectra analysis. In the first case, a full structure elucidation was performed on E. coli serogroup O63, and in the second case a demonstration of the bioinformatics approach is done to E. coli serogroup O93. In the sixth chapter, a new version of the CarbBuilder software is presented. This includes a more robust building algorithm that helps build sterically crowded polysaccharide structures, as well as a general expansion of possible components. 

  • 130.
    Sundén, Henrik
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Organocatalytic Domino Reactions2007Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Organocatalyzed reactions involving activation strategies of ketones and aldehydes are important processes in organic chemistry. These activation strategies serve as a versatile platform for the construction of several domino reactions. This thesis describes the development of six new asymmetric or-ganocatalyzed domino reactions for the enantioselective formation of carbo-cycles or heterocycles. The domino reactions are based on two major activation pathways the domino “iminium-enamine” and the domino “enamine-iminium”. Making use of the domino “iminium-enamine” reaction, 2H-1-benzopyrans, 2H-1-benzothiopyrans and 1,2-dihydroquinolines and cyclopropanes can be obtained in high yields and excellent ee´s. Via the amine-catalyzed domino “enamine-iminium” reaction the synthesis of aza-Diels-Alder and Diels-Alder products can be achieved with high ee´s and yields. Moreover, a mechanistic model is proposed for each reaction that enables the stereochemical outcome of the reaction to be predicted.

  • 131.
    Svansson, Lars
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Synthesis of a heptasaccharide and some 3'-C-branched nucleoside analogues1992Doctoral thesis, comprehensive summary (Other academic)
  • 132.
    Säwén, Elin
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    NMR spectroscopy and MD simulations of carbohydrates2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Knowledge about the structure, conformation and dynamics of carbohydrates is important in our understanding of the way carbohydrates function in biological systems, for example in intermolecular signaling and recognition. This thesis is a summary of five papers studying these properties in carbohydrate-containing molecules with NMR spectroscopy and molecular dynamics simulations.

    In paper I, the ring-conformations of the six-membered rings of two carbaiduronic analogs were investigated. These carbasugars could potentially be used as hydrolytically stable mimics of iduronic acid in drugs. The study showed that the equilibrium is entirely shifted towards the 4C1 conformation.

    Paper II is an investigation of the conformational flexibility and dynamics of two (1→6)-linked disaccharides related to an oligosaccharide epitope expressed on malignant tumor cells.

    In paper III, the conformational space of the glycosidic linkage of an alfa-(1→2) linked mannose disaccharide present in N- and O-linked glycoproteins, was studied. A maximum entropy analysis using different priors as background information was used and four new Karplus equations for 3JC,C and 3JC,H coupling constants, related to the glycosidic linkage, were presented.

    Paper IV describes a structural elucidation of the exopolysaccharide (EPS) produced by Streptococcus thermophilus ST1, a major dairy starter used in yoghurt and cheese production. The EPS contains a hexasaccharide repeating unit of d-galactose and d-glucose residues, which is a new EPS structure of the S. thermophilus species.

    In paper V, the dynamics of three generations of glycodendrimers were investigated by NMR diffusion and 13C NMR relaxation studies. Three different correlations times were identified, one global correlation time describing the rotation of the dendrimer as a whole, one local correlation time describing the reorientation of the C-H vectors, and one correlation time describing the pulsation of a dendrimer branch.

  • 133.
    Tejbrant, Jan
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    An approach to the synthesis of O-glycopeptides1992Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Synthesis of glycopeptides using a solid phase technique has been performed. The preparation of suitably protected glycosylated amino acids and the successful use of these derivatives in solid phase synthesis of two glycopeptides are described. The target molecules were the minimal epitope of the monoclonal antibody FDC6 towards oncofetal human Fibronectin, and a glycosylated cyclic peptide related to the first loop of the EGFlike domain of bovine factor IX.

  • 134.
    Teodorovic, Peter
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Synthesis of oligosaccharides related to the capsular polysaccharide of Neisseria meningitidis serotype A2005Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In order to find suitable stable vaccine candidates against Neisseria meningitidis group A, several structures related to the capsular polysaccharide have been synthesised. The first part of the thesis describes the synthesis of C-phosphonate analogues starting from glucose. The key step is a Mitsunobu coupling of a methyl C-phosphonate monomer to the 6-hydroxyl group of a 2-acetamido mannose derivative. Contained within this work is a description of an improved synthesis of 2-azido-2-deoxy-D-mannopyranose. The second part outlines the synthesis of structural elements present in the native capsular polysaccharide of Neisseria meningitidis serotype A including different acetylation and phosphorylation patterns. The final chapter describes an improved synthesis of the Lewis b hexasaccharide needed for purification of and interaction studies with the Helicobacter pylori adhesin BabA.

  • 135.
    Thalén, Lisa K.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Transition Metal- and Enzyme-Catalyzed Reactions of Primary Amines and Allylic Alcohols: Powerful Tools in the Preparation of Pharmaceutically Important Compounds2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Dynamic kinetic resolution (DKR) has been applied to primary amines utilizing a ruthenium catalyst and an (R)-selective lipase to provide the corresponding amides in up to 95% isolated yield and up to >99% ee. Further investigations of the chemoenzymatic DKR of amines show that it is general and can be applied to a wide range of amines. The protocol was found to be applicable with both isopropyl acetate and dibenzyl carbonate as acyl donors. In the latter case, release of the free amine from the carbamate products was carried out under very mild conditions. A new route to prepare norsertraline, an antidepressant, utilizing DKR as one of the key steps has also been developed.

    Further investigations of the DKR of 1-phenylethylamine led to the development of a protocol that could be used on gram scale. Several parameters were studied including catalyst loading, acyl donor used, and concentration of the reaction. The Ru-catalyst loading was decreased from 4 mol% to 1.25 mol% and the enzyme catalyst loading was decreased from 40 mg/mmol substrate to 10 mg/mmol substrate.

    The racemization of pipecoloxylidide, an intermediate in the synthesis of commonly used anesthetics, was carried out. This racemization method was developed for its potential use in an integrated process that combines enantiomer separation techniques and racemization of the undesired enantiomer. The integration of racemization of the undesired enantiomer would increase the overall yield of the desired enantiomer and thus make the procedure highly efficient.

    DKR has also been applied to allylic alcohols utilizing a ruthenium catalyst and either an (R)-selective lipase or an (S)-selective protease to provide the corresponding allylic esters in high yield and high ee. A copper-catalyzed allylic substitution was then applied to provide the corresponding alkenes with inversion of stereochemistry. Subsequent C-C double bond cleavage afforded pharmaceutically important a-methyl substituted carboxylic acids in high ee.

  • 136.
    Thelin, Mats
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Nucleoside H-phosphonates and H-phosphonothioates: some chemical and stereochemical studies1992Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Phosphonic acid's reaction towards sterically hindered acyl chlorides has been investigated. A new synthetic method for the synthesis of nucleoside Hphosphonate monoesters has been developed. Furthermore, a method for the synthesis of nucleoside H-phosphonothioate monoesters has also been developed. Some chemical and stereochemical aspects of ribonucleoside Hphosphonate and H-phosphonothioate synthesis have been studied. Three new reagents are described, which oxidize nucleoside H-phosphonates and Hphosphonothioates into corresponding phosphates, thiophosphates and selenophosphates.

  • 137.
    Tidén, Anna-Karin
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Syntheses of Haemophilus influenzae typed d and e antigens, each containing a 2-acetamido-2-deoxy-ss-D-mannopyranosyluronic acid residue, and of analogues and derivatives of 3,6-di-O-α-D-mannopyranosyl-α-D-mannopyranoside1991Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Syntheses ofp-nitrophenyl 2-acetamido-3-0-(2-acetamido-2-deoxy-ß-Dglucopyranosyl)- 2-deoxy-ß-D-mannopyranosiduronic acidand p- -trifiuoroacetamidophenyl2-acetamido-4-0-(2-acetamido-2-deoxy-ß-D- -glucopyranosyl)-2-deoxy-ß-D-mannopyranosiduronic acid that corresponds to the repeating units of Haemophilus influenzae type d and e capsular antigens, are discussed. These were needed for immunological studies. Analogues and derivatives of 3,6-di-O-a-D-mannopyranosyl-oc-D-mannopyranoside were synthesised and the syntheses of these and their potential biological value is discussed.

  • 138.
    Tinnis, Fredrik
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Catalytic Formation of Amides2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The amide functionality is a highly important chemical bond, found in a great number of synthetic products such as pharmaceuticals, polymers and agrochemicals. The focus of this thesis has been directed towards efficient, mild and environmentally friendly methods for amide formations. The first part is devoted to the investigation of a Lewis acid catalyzed protocol for direct condensation of non-activated carboxylic acids and amines. ZrCl4 was found to be a highly active catalyst and a low catalytic loading enabled for high yields of secondary and tertiary amides under relatively mild conditions. The second part of the thesis describes our investigations towards a catalytic method for primary amides. We demonstrated that the transformation was feasible by performing minor alterations to the previous Lewis acid based procedure. A variety of primary amides could be obtained in high yields by the use of carbamates, as a non-gaseous source of ammonia in combination with carboxylic acids and catalytic amounts of TiCl4 or ZrCl4. Furthermore, the protocol was extended to include catalytic formation of N,N-dimethylamides from non-activated carboxylic acids.

    The use of immobilized metal nanoparticles as heterogeneous catalysts has emerged as a highly investigated research area. The final chapter of this thesis deals with the successful application of an immobilized Pd nanocatalyst for amide formation via the aminocarbonylation reaction of aryl iodides. The Pd0-AmP-MCF catalyst was found to operate through a “release and catch” mechanism, in which PdII species were released into the solution and then re-deposited onto the support after completion of the reaction. It was discovered that the combination of aryl halide and amine was the cause of the leaching, and furthermore that the homogeneous Pd species catalyzed the aminocarbonylation reaction. A selection of aryl iodides were evaluated using 2 mol% of Pd0-AmP-MCF under atmospheric pressure of CO, and the corresponding amides were obtained in good to high yields.

  • 139.
    Tran, Lien-Hoa
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Biomimetic Reactions: Water Oxidation and Aerobic Oxidation2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis deals mainly with two oxidation reactions: water oxidation and aerobic oxidation, both of which have been applied in a biomimetic fashion. In the former reaction molecular oxygen is generated whereas in the latter it was used as terminal oxidant in oxidation reactions.

    The first part of this thesis describes the synthesis of different ruthenium and manganese complexes that could potentially act as catalysts for water oxidation. This part includes a discussion of the stability and reactivity of a new manganese(III) amide-type complex, that has been used as a catalyst for both epoxidation of stilbene and alcohol oxidation.

    The second part of this thesis discusses the synthesis of two new hybrid catalysts consisting of hydroquinone linked cobalt(II) salophen and cobalt(II) salmdpt, which have been used as oxygen-activating catalysts in aerobic oxidation reactions. The former catalyst was applied to the Pd-catalyzed reactions such as 1,4-diacetoxylation of cyclohexadiene whereas the latter was applied to the Ru-catalyzed oxidation of secondary alcohols to ketones. Moreover, these two hybrid catalysts could be used in the Pd-catalyzed carbocyclization of enallenes. In all cases molecular oxygen was used as the stoichiometric oxidant.

     

  • 140.
    Träff, Annika
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Asymmetric transformation of ß- and γ-functionalized alcohols: Study of combined ruthenium-catalyzed racemization and enzymatic resolution2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The major part of this thesis describes the asymmetric synthesis of β- and γ-amino alcohols through the combination of ruthenium catalyzed racemization and enzymatic kinetic resolution.

    The dynamic kinetic resolution, DKR, protocol for chlorohydrins was improved by employing Bäckvall’s catalyst, which is a base activated racemization catalyst, in combination with Burkholderia cepacia lipase. These optimized conditions broadened the substrate scope and improved the yields and ee’s of the obtained chlorohydrin acetates. The utility of the method was demonstrated in the synthesis of (S)-salbutamol.

    In the second part of the thesis, DKR was utilized in the enantio-determining step of the total synthesis of (R)-duloxetine. Optimized DKR conditions, combining Bäckvall’s catalyst together with Candida antarctica lipase B, afforded a β-cyano acetate in high yield and ee. (R)-Duloxetine was accessible through synthetic alterations of the enantioenriched β-cyano acetate in high overall yield.

    A dynamic kinetic asymmetric transformation, DYKAT, protocol to obtain enantio- and diastereomerically pure γ-amino alcohols was developed. In a first step N-Boc-aminoketones were obtained in high enantiomeric purity through a proline-catalyzed Mannich reaction. Subsequent in situ reduction coupled with a highly efficient DYKAT yielded γ-amino acetates in high dr and ee. The γ-amino alcohols were available through simple hydrolysis/deprotection with retained stereochemistry.

    In the final part of the thesis a heterogeneous bifunctional catalytic system is reported, which combines the catalytic properties of transition metal-catalyzed racemization with enzymatic acylation. A novel ruthenium-phosphonate complex was synthesized and then covalently anchored to the active site of solid supported Candida antarctica lipase B. The partially inhibited beads proved to be catalytically active both in racemization as well as enzymatic acylation.

  • 141.
    Utas, Josefin
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Hydrogen Bonded Phenols as Models for Redox-Active Tyrosines in Enzymes2006Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis deals with the impact of hydrogen bonding on the properties of phenols. The possibility for tyrosine to form hydrogen bonds to other amino acids has been found to be important for its function as an electron transfer mediator in a number of important redox enzymes. This study has focused on modeling the function of tyrosine in Photosystem II, a crucial enzyme in the photosynthetic pathway of green plants.

    Hydrogen bonds between phenol and amines in both inter- and intramolecular systems have been studied with quantum chemical calculations and also in some solid-state structures involving phenol and imidazole.

    Different phenols linked to amines have been synthesized and their possibilities of forming intra- and intermolecular hydrogen bonds have been studied as well as the thermodynamics and kinetics of the generation of phenoxyl radicals via oxidation reactions.

    Since carboxylates may in principle act as hydrogen bond acceptors in a manner similar to imidazole, proton coupled electron transfer has also been studied for a few phenols intramolecularly hydrogen bonded to carboxylates with the aim to elucidate the mechanism for oxidation. Electron transfer in a new linked phenol—ruthenium(II)trisbipyridine complex was studied as well.

    The knowledge is important for the ultimate goal of the project, which is to transform solar energy into a fuel by an artificial mimic of the natural photosynthetic apparatus

  • 142.
    van der Werf, Angela
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Transformations of Nitrosoarenes and Alkynyl Enones: Selective Synthesis of Nitrogen-Containing Compounds2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The nitrogen atom plays a unique role in organic chemistry. It is abundantly found in organic materials and is responsible for the activity of many biologically relevant compounds. In this thesis, nitrosoarenes and keto- and pyridyl-substituted enynes are used as convenient starting materials for the selective synthesis of nitrogen-containing compounds.

    Nitrosoarenes are versatile compounds that can undergo a broad range of reactions. The nature of the nitroso group is significantly different from that of related nitrogen-based functional groups and this can be used as an advantage in the development of new methodology. In the first part of this thesis, the para-selective halogenation of nitrosoarenes with copper(II) halides as halogenating reagents is explored. The one-pot transformation of the products to the corresponding nitroarenes and anilines is demonstrated. The use of nitrosoarenes for radical N-perfluoroalkylation is presented in the next chapters. N-Perfluoroalkylation is a relatively new field and only a limited number of reagents and substrates have been employed so far. In this thesis, the stable and convenient Langlois reagent was used to achieve selective N-trifluoromethylation of nitrosoarenes to obtain the corresponding hydroxylamines. Longer perfluoroalkyl chains were investigated as well, but the less stable products were defluorinated to form hydroxamic acid derivatives. These products could be reduced to yield perfluoroalkyl amides.

    Keto- and pyridyl-substituted enynes are starting materials designed to undergo cyclization reactions in the presence of a metal catalyst and a nucleophile. This offers the possibility to obtain a variety of more complex molecular structures in a single step. In the second half of the thesis, the reaction between these starting materials and enamines is explored. A range of cyclopenta[c]furans were synthesized in good yields and with high diastereoselectivities from alkynyl enones and enamines with InBr3 as the catalyst. The enamines were formed in situ in a multicomponent reaction. Pyridyl-substituted enynes are the pyridine analogues of alkynyl enones and were found to form polycyclic indolizines in the reaction with cyclic enamines with AgOTf as a catalyst. Good yields and high to excellent diastereoselectivities were obtained. When the reaction was performed with in situ-generated enamines, different indolizine derivatives were obtained.

  • 143.
    Verboom, Renzo C.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Palladium(II)-catalyzed intramolecular 1,4-oxyacyloxylation of conjugated dienes2004Doctoral thesis, comprehensive summary (Other academic)
  • 144.
    Verho, Oscar
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Transition Metal-Catalyzed Redox Reactions: A Journey from Homogeneous Ruthenium to Heterogeneous Palladium Catalysis2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The first part of the thesis covers the development and utilization of electronically modified (pentaarylcyclopentadienyl)Ru-complexes in the racemization of secondary alcohols. This study revealed that the electronic properties of the substrate were the main factors dictating whether β-hydride elimination or hydride re-addition becomes the rate-determining step of the racemization process. With this knowledge in hand, it proved to be possible to design more efficient racemization protocols by matching the electronic properties of catalyst and substrate.

    The second part describes mechanistic work that aimed at elucidating the role of CO dissociation in the mechanism of secondary alcohol racemization catalyzed by a (pentaarylcyclopentadienyl)Ru-complex. From CO exchange studies, we demonstrated that CO dissociation occurred in the catalytically active tert-BuO-species as well as in the chloride precatalyst. Furthermore, an inhibition study showed that an increase of the partial pressure of CO had a negative influence on the racemization rate. Together, these two observations provide strong support for CO dissociation as a key step in the racemization of secondary alcohols.

    The third part concerns the improved synthesis and characterization of a heterogeneous catalyst consisting of Pd nanoparticles immobilized on aminopropyl-functionalized siliceous mesocellular foam. The developed Pd nanocatalyst was found to be a highly efficient and recyclable catalyst for the aerobic oxidation of a wide range of primary and secondary alcohols to the corresponding aldehydes and ketones.

    The fourth part deals with the successful application of the Pd nanocatalyst in chemically-induced H2O oxidation, when using either ceric ammonium nitrate or [Ru(bpy)3]3+ as the terminal oxidant. Remarkably, the Pd nanocatalyst proved to catalyze this reaction with high efficiency and the measured TOF was found to greatly exceed those of current state-of-the-art metal oxide catalysts.

    The fifth and final part describes the co-immobilization of Pd nanoparticles and the enzyme Candida Antarctica Lipase B into the same cavities of mesocellular foam, to generate a “metalloenzyme-like” hybrid catalyst for the dynamic kinetic resolution of a primary amine. The close proximity of the two catalytic species led to an enhanced cooperativity between them and resulted in an overall more efficient tandem process. 

  • 145.
    Volkov, Alexey
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Catalytic Amide Reductions under Hydrosilylation Conditions2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis covers the development of catalytic methodologies for the mild and chemoselective reductions of amides. The first part of the thesis describes the use of a Fe(II)/NHC catalyst for the deoxygenation of aromatic tertiary amides to corresponding amines. The protocol is characterized by low catalyst loading, mild reaction conditions and the use of air and moisture stable polymethylhydrosilaxane (PMHS) as the hydride source.

    The second part concerns the development of a protocol for the room temperature deoxygenation of a wide range of tertiary amides to amines using catalytic amounts of Et2Zn and LiCl together with PMHS. The system displayed high levels of chemoselectivity tolerating various reducible groups such as nitro, nitrile, and olefin functionalities, and was shown to be applicable for the reduction of aromatic, heteroaromatic and aliphatic tertiary amides.

    The attempts to expand the scope of the Fe-based protocol to accommodate benzylic tertiary amides led to the development of a transition metal-free catalytic system based on KOtBu for the formation of enamines. The final products constitute an important class of precursors for a wide range of valuable compounds in organic chemistry. Moreover, avoiding the use of transition metals in the protocol allowed the desired products to be obtained without the hazardous metal contaminants.

    The last chapter of the thesis describes the Mo(CO)6-catalyzed hydrosilylation of amides. The Mo-based catalyst was proven to mediate the deoxygenation of α,β-unsaturated tertiary and secondary amides to the corresponding allylamines without reduction of the olefinic bonds. Further development of the catalytic system revealed an unprecedented chemoselectivity in the hydrosilylation of aromatic and certain aliphatic tertiary amides in the presence of a variety of reducible groups along with aldehydes and imines that were tolerated for the first time. Moreover, it was possible to control the reaction outcome by variation of the reaction temperature to obtain either amines or aldehydes as the major products. The synthetic utility of the developed Mo(CO)6-catalyzed protocols was further demonstrated in the synthesis of the pharmaceuticals Naftifine and Donepezil.

  • 146.
    Västilä, Patrik
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Development of highly modular ligands for use in asymmetric transition-metal catalyzed reactions2005Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The synthesis and evaluation of ligands for use in asymmetric transition metal catalyzed reactions is a widely used concept to achieve improved enantioselectivity in a variety of different transformations. The present thesis decribes the synthesis of a number of different oxazoline-based ligands and their use in titanum-catalyzed addition of diethyl zinc to aliphatic and aromatic aldehydes. Interestingly, the presence of catalytic amounts of titanium in our system was sufficient to achieve effective catalysis in contrast to what has been previously reported concerning titanium-catalyzed addition of diethyl zinc to aldehydes.

    The synthesis and evaluation of a library of novel dipeptide-like ligands are described and these ligands were employed in connection with ruthenium-catalyzed transfer hydrogenation of aromatic ketones. Excellent enantioselectivities and yields were obtained.

    Furthermore, the novel concept of forming the ligand and catalyst in situ in a one-pot system was explored. In addition to significant simplification, this approach resulted in improvements in both enantioselectivity (minor) and reaction rate (2-3 fold) compared to previously studied procedures.

    The surprizing influence of alkali salts on ruthenium-catalyzed transfer hydrogenation involving these dipeptide-like ligands are described and discussed. In the presence of these additives the ruthenium-catalyzed transfer hydrogenation performed with higher enantioselecitvity and reactivity.

    Finally, mechanistic studies concerning ruthenium-catalyzed transfer hydrogenation involving the dipeptide-like ligands are also described and discussed.

  • 147.
    Wallner, Olov
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Palladium-Catalyzed Synthesis and Transformations of Organometallic Compounds2006Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis is focused on two important fields of palladium catalysis: the development of electrophilic allylic substitution reactions via bis-allylpalladium intermediates; and application of palladium pincer-complexes in the synthesis and transformations of organometallic compounds.

    Palladium-catalyzed electrophilic allylation of aldehyde and imine substrates could be achieved using readily available allyl chlorides and acetates by employing hexamethylditin or bis(pinacolato)diboron reagents. The reaction proceeds under mild and neutral reaction conditions with high regioselectivity, providing the branched homoallylic products. The stereoselectivity of the reaction depends on the steric and electronic effects of the allylic substituents of the substrates. DFT modeling of the electrophilic attack on the bis-allylpalladium intermediate of the reaction revealed the origin of the regio- and stereoselectivity of the reaction.

    Palladium pincer-complexes were employed as catalysts in a variety of reactions such as stannylation, selenylation, allylation, and cross coupling reactions with various electrophiles. Allylic stannylation in the presence of hexamethylditin was achieved by use of an NCN palladium pincer-complex catalyst. In contrast to the reactions catalyzed by traditional palladium catalysts, isolation of functionalized allyl stannanes was possible due to the special features of the pincer-complex catalyst. Extension of the scope of the palladium pincer-complex catalyzed electrophilic allylation reactions was achieved by using potassium trifluoro(allyl)borate instead of allyl stannanes. In addition, asymmetric electrophilic allylation of sulfonimines was achieved by employment of novel BINOL-based palladium pincer-complexes. The enantioselectivity of the pincer-complex catalyst was fine-tuned by employment of substituted analogs of BINOL.

  • 148.
    Wang, Dong
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    New Reactions with Allyl- and Allenylboron Reagents: Transition-Metal-Catalyzed and Transition-Metal-Free Carbon-Carbon Bond Formation Processes2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Organoboron compounds have been widely used in carbon-carbon bond formation reactions in organic synthesis and catalysis. This thesis is focused on cross-coupling reactions of allyl-, allenylboronic acids and their ester derivatives via transition metal catalysis or transition-metal-free processes.

    The first part of the thesis describes Cu-catalyzed C(sp3)-C(sp3) formation reactions involving allylboronic acids and α-diazoketones. This coupling process shows high γ-regioselectivity, resulting in branched allylic products. When stereodefined cyclic allylboronic acids were employed as the substrate, the relative facial configuration was retained in the reaction product.

    The second part involves Pd-catalyzed cross-coupling of allylboronic acid and α-diazoketones. The reaction proceeds with high α-regioselectivity, affording linear allylic products. Accordingly, the palladium- and copper-catalyzed cross-coupling of allylboronic acid and α-diazoketones occurs with opposite regioselectivity.

    The third part concerns a new transition-metal-free carbon-carbon bond formation between allenylboronic acids and in situ generated diazo compounds. The diazo compounds are generated from tosylhydrazones in the presence of base. The reaction is suitable for synthesis of densely substituted conjugated dienes with high Z-selectivity.

    In the final part, the allylation of quinones with allylboronates is presented. The reaction was performed without any catalyst or additive. Various quinones can be employed as substrates, including unsubstituted, monosubstituted benzoquinones and naphthoquinones.

  • 149.
    Warner, Madeleine
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Ruthenium-Catalyzed Hydrogen Transfer Reactions: Mechanistic Studies and Chemoenzymatic Dynamic Kinetic Resolutions2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The main focus of this thesis lies on transition metal-catalyzed hydrogen transfer reactions. In the first part of the thesis, the mechanism for racemization of sec-alcohols with a ruthenium complex, Ru(CO)2Cl(η5-C5Ph5) was studied.

    The reaction between 5-hexen-2-ol and Ru(CO)2(Ot-Bu)(η5-C5Ph5) was studied with the aim to elucidate the origin of the slow racemization observed for this sec-alcohol. Two diastereomers of an alkoxycarbonyl complex, which has the double bond coordinated to ruthenium, were characterized by NMR and in situ FT-IR spectroscopy. The observed inhibition of the rate of racemization for substrates with double bonds provided further confirmation of the importance of a free coordination site on ruthenium for β-hydride elimination. Furthermore, we observed that CO exchange, monitored by 13C NMR using 13CO, occurs with both the precatalyst, Ru(CO)2Cl(η5-C5Ph5), and the active catalytic intermediate, Ru(CO)2(Ot-Bu)(η5-C5Ph5). It was also found that added CO has an inhibitory effect on the rate of racemization of (S)-1-phenylethanol. Both these observations provide strong support for reversible CO dissociation as a key step in the racemization mechanism.

    In the second part of this thesis, Ru(CO)2Cl(η5-C5Ph5) was combined with an enzymatic resolution catalyzed by a lipase, leading to several efficient dynamic kinetic resolutions (DKR). DKR of exocyclic allylic alcohols afforded the corresponding acetates in high yields and with excellent enantiomeric excess (ee). The products were utilized as synthetic precursors for α-substituted ketones and lactones. DKR of a wide range of homoallylic alcohols afforded the products in good to high yields and with high ee. The homoallylic acetates were transformed into 5,6-dihydropyran-2-ones in a short reaction sequence. Furthermore, DKR of a wide range of aromatic β-chloroalcohols afforded the products in high yields and with excellent ee. The β-chloro acetates were further transformed into chiral epoxides.

  • 150.
    Wettergren, Jenny
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Selective transfer hydrogenations: Catalyst development and mechanistic investigations2008Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    By generating a library of amino acid-based ligands, pseudo-dipeptides, and combining them with transition metals, we have created selective and efficient ruthenium and rhodium catalysts for the asymmetric transfer hydrogenation of ketones. The ruthenium-catalyzed reaction was studied in detail, and we found that alkali metals play a crucial role for the reactivity and selectivity of the reaction. Furthermore, we have performed kinetic studies on the catalytic system, and the experimental data does neither support the established inner-sphere nor the classical outer-sphere mechanism. Hence, a novel mechanism for the ruthenium-pseudo-dipeptide-catalyzed transfer hydrogenation is proposed. In this unprecedented outer-sphere mechanism, a hydride and an alkali metal ion are transferred from the donor to the ruthenium complex in the rate determining step.

    In addition, the pseudo-dipeptide ligands were employed in the rhodium-catalyzed transfer hydrogenation of aryl alkyl ketones to yield the corresponding alcohols in high yields and excellent enantioselectivities (up to 98% ee). The study revealed that the alkali metals, so important in the ruthenium analogue of the reaction, do not improve the enantioselectivity of the reaction. Deuterium labeling experiments showed that the reaction follows the mono hydridic route.

    Furthermore, a novel method for efficient catalyst screening has been developed. We have demonstrated that ligand synthesis, catalyst formation, and enantioselective catalysis can be performed using an in situ one-pot procedure. The efficacy of the concept was demonstrated in the enantioselective reduction of ketones. In addition to the simplification of the catalyst formation, this approach resulted in improvement of the product ee.

    Finally, the development of a reduction protocol for the transfer hydrogenation of ketones to alcohols without the involvement of transition metal catalysts is described. Using microwave irradiation, a range of ketones was efficiently reduced in high yields using catalytic amounts of lithium 2-propoxide in 2-propanol.

1234 101 - 150 of 159
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf