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  • 1.
    Bartholomeyzik, Teresa
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Pendrill, Robert
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Lihammar, Richard
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Jiang, Tuo
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-E.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Kinetics and Mechanism of the Palladium-Catalyzed Oxidative Arylating Carbocyclization of Allenynes2018In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 140, no 1, p. 298-309Article in journal (Refereed)
    Abstract [en]

    Pd-catalyzed C-C bond-forming reactions under oxidative conditions constitute a class of important and widely used synthetic protocols. This Article describes a mechanistic investigation of the arylating carbocyclization of allenynes using boronic acids and focuses on the correlation between reaction conditions and product selectivity. Isotope effects confirm that either allenic or propargylic C-H activation occurs directly after substrate binding. With an excess of H2O, a triene product is selectively formed via allenic C-H activation. The latter C-H activation was found to be turnover-limiting and the reaction zeroth order in reactants as well as the oxidant. A dominant feature is continuous catalyst activation, which was shown to occur even in the absence of substrate. Smaller amounts of H2O lead to mixtures of triene and vinylallene products, where the latter is formed via propargylic C-H activation. The formation of triene occurs only in the presence of ArB(OH)(2). Vinylallene, on the other hand, was shown to be formed by consumption of (ArBO)(3) as a first-order reactant. Conditions with sub-stoichiometric BF3 center dot OEt2 gave selectively the vinylallene product, and the reaction is first order in PhB(OH)(2). Both C-H activation and transmetalation influence the reaction rate. However, with electron-deficient ArB(OH)(2), C-H activation is turnover-limiting. It was difficult to establish the order of transmetalation vs C-H activation with certainty, but the results suggest that BF3 center dot OEt2 promotes an early transmetalation. The catalytically active species were found to be dependent on the reaction conditions, and H2O is a crucial parameter in the control of selectivity.

  • 2.
    Brea, Oriana
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Mó, Otilia
    Yáñez, Manuel
    Merced Montero-Campillo, M.
    Alkorta, Ibon
    Elguero, José
    Are beryllium-containing biphenyl derivatives efficient anion sponges?2018In: Journal of Molecular Modeling, ISSN 1610-2940, E-ISSN 0948-5023, Vol. 24, no 1, article id 16Article in journal (Refereed)
    Abstract [en]

    The structures and stabilities of 2,2'-diBeX-1,1'-biphenyl (X = H, F, Cl, CN) derivatives and their affinities for F-, Cl-, and CN- were theoretically investigated using a B3LYP/6-311 + G(3df, 2p)//B3LYP/6-31 + G(d,p) model. The results obtained show that the 2,2'-diBeX-1,1'-biphenyl derivatives (X = H, F, Cl, CN) exhibit very high F-, Cl-, and CN- affinities, albeit lower than those reported before for their 1,8-diBeX-naphthalene analogs, in spite of the fact that the biphenyl derivatives are more flexible than their naphthalene counterparts. Nevertheless, some of the biphenyl derivatives investigated are predicted to have anion affinities larger than those measured for SbF5, which is considered one of the strongest anion capturers. Therefore, although weaker than their naphthalene analogs, the 2,2'-diBeX-1,1'-biphenyl derivatives can still be considered powerful anion sponges. This study supports the idea that compounds containing -BeX groups in chelating positions behave as anion sponges due to the electron-deficient nature and consequently high intrinsic Lewis acidity of these groups.

  • 3. Daikoku, S.
    et al.
    Pendrill, Robert
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Kanie, Y.
    Ito, Y.
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Kanie, O.
    Synthesis and structural investigation of a series of mannose-containing oligosaccharides using mass spectrometry2018In: Organic and biomolecular chemistry, ISSN 1477-0520, E-ISSN 1477-0539, Vol. 16, no 2, p. 228-238Article in journal (Refereed)
    Abstract [en]

    A series of compounds associated with naturally occurring and biologically relevant glycans consisting of alpha-mannosides were prepared and analyzed using collision-induced dissociation (CID), energy-resolved mass spectrometry (ERMS), and H-1 nuclear magnetic resonance spectroscopy. The CID experiments of sodiated species of disaccharides and ERMS experiments revealed that the order of stability of mannosyl linkages was as follows: 6-linked > 4-linked >= 2-linked > 3-linked mannosyl residues. Analysis of linear trisaccharides revealed that the order observed in disaccharides could be applied to higher glycans. A branched trisaccharide showed a distinct dissociation pattern with two constituting disaccharide ions. The estimation of the content of this ion mixture was possible using the disaccharide spectra. The hydrolysis of mannose linkages at 3- and 6-positions in the branched trisaccharide revealed that the 3-linkage was cleaved twice as fast as the 6-linkage. It was observed that the solution-phase hydrolysis and gas-phase dissociation have similar energetics.

  • 4.
    Gudmundsson, Arnar
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Gustafson, Karl P. J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Yang, Bin
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Himo, Fahmi
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-E.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Efficient Formation of 2,3-Dihydrofurans via Iron-Catalyzed Cycloisomerization of alpha-Allenols2018In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 8, no 1, p. 12-16Article in journal (Refereed)
    Abstract [en]

    Herein, we report a highly efficient iron-catalyzed intramolecular nucleophilic cyclization of alpha-allenols to furnish substituted 2,3-dihydrofurans under mild reaction conditions. A highly diastereoselective variant of the reaction was developed as well, giving diastereomeric ratios of up to 98:2. The combination of the iron-catalyzed cycloisomerization with enzymatic resolution afforded the 2,3-dihydrofuran in high ee. A detailed DFT study provides insight into the reaction mechanism and gives a rationalization for the high chemo-and diastereoselectivity.

  • 5.
    Görbe, Tamás
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Lihammar, Richard
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-E.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Heterogeneous Acid-Catalyzed Racemization of Tertiary Alcohols2018In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 24, no 1, p. 77-80Article in journal (Refereed)
    Abstract [en]

    Tertiary alcohols are important structural motifs in natural products and building blocks in organic synthesis but only few methods are known for their enantioselective preparation. Chiral resolution is one of these approaches that leaves one enantiomer (50% of the material) unaffected. An attractive method to increase the efficiency of those resolutions is to racemize the unaffected enantiomer. In the present work, we have developed a practical racemization protocol for tertiary alcohols. Five different acidic resin materials were tested. The Dowex 50WX8 was the resin of choice since it was capable of racemizing tertiary alcohols without any byproduct formation. Suitable solvents and a biphasic system were investigated, and the optimized system was capable of racemizing differently substituted tertiary alcohols.

  • 6. Ibrahem, Ismail
    et al.
    Iqbal, Muhammad Naeem
    Stockholm University, Faculty of Science, Department of Organic Chemistry. Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Verho, Oscar
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Eivazihollagh, Alireza
    Olsén, Peter
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Edlund, Håkan
    Tai, Cheuk-Wai
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Norgren, Magnus
    Johnston, Eric V.
    Copper Nanoparticles on Controlled Pore Glass and TEMPO for the Aerobic Oxidation of Alcohols2018In: ChemNanoMat, ISSN 2199-692X, Vol. 4, no 1, p. 71-75Article in journal (Refereed)
    Abstract [en]

    Herein, we report on the facile synthesis of a heterogeneous copper nanocatalyst and its combination with 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) for the aerobic oxidation of alcohols to their corresponding carbonyl compounds. This low cost copper nanocatalyst was found to exhibit excellent recyclability, making it a highly attractive catalytic system from an economical and environmental point of view. Extensive characterization of the catalyst by a number of techniques revealed that it was comprised of well-dispersed Cu(I/II) nanoparticles with an average size of around 6nm.

  • 7.
    Kerdphon, Sutthichat
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    NHC,P- and N,P-Iridium Catalysts for Hydrogenations and Hydrogen Transfer Reactions2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The work described in this thesis is focused on hydrogenation and hydrogen transfer reactions using iridium catalysts. The first part concerns the use of N-heterocyclic carbene-phosphine iridium complexes in alkylation reactions (Chapters 2 and 3) and the hydrogenation of ketones (Chapter 4). A number of N-heterocyclic carbene-phosphine iridium complexes have been prepared and evaluated as catalysts for C-N bond formation of amides using alcohols as the electrophile. This catalytic system can be used with a wide range of substrates at low catalyst loading (only 0.5 mol%) to furnish the desired products in up to 98% isolated yield. The achiral N-heterocyclic carbene-phosphine iridium complexes were also found to catalyze the methylation of ketones with methanol under mild conditions to afford the mono-methylated products in up to 98% isolated yield with low catalyst loading (1.0 mol%). Additionally, several chiral N-heterocyclic carbene-phosphine iridium complexes were synthesized and evaluated in asymmetric hydrogenation of ketones. The reactions were carried out at room temperature under base-free conditions to obtain the chiral alcohols in up to 96% ee in 30 minutes.

    The second part of this thesis (Chapter 5) details the preparation of new N,P-iridium complexes which were found to be highly efficient catalysts for the asymmetric hydrogenation of challenging tetrasubstituted olefins. This catalytic system results in optically active compounds of high enantiomeric excess (up to 98% ee) as the single diasteroisomer.

  • 8.
    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.

  • 9. Tutkowski, Brandon
    et al.
    Kerdphon, Sutthichat
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Limé, Elaine
    Helquist, Paul
    Andersson, Pher G.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Wiest, Olaf
    Norrby, Per-Ola
    Revisiting the Stereodetermining Step in Enantioselective Iridium-Catalyzed Imine Hydrogenation2018In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 8, no 1, p. 615-623Article in journal (Refereed)
    Abstract [en]

    The mechanism for the iridium-catalyzed asymmetric hydrogenation of prochiral imines has been investigated for an experimentally relevant ligand substrate combination using DFT calculations. The possible stereoisomers of the stereodetermining hydride transfer transition state were considered for four possible hydrogenation mechanisms starting from the recently disclosed active catalyst consisting of iridium phosphine-oxazoline with cyclometalated imine substrate. The hydrogenation was found to proceed via an outer sphere pathway. The transition state accurately describes the experimental observations of the active catalyst and provides a structural rationale for the high stereoinduction despite the lack of direct interaction points in the outer-sphere mechanism. The predicted enantioselectivity was consistent with experimental observations. Experimental studies support the hypothesis that the iridacycle forms spontaneously and functions as the active catalyst in the hydrogenation.

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