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  • 1.
    Ghosh, Raju
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Stridfeldt, Elin
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Olofsson, Berit
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Metal-Free One-Pot Synthesis of Benzofurans2014In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 20, no 29, p. 8888-8892Article in journal (Refereed)
    Abstract [en]

    Ethyl acetohydroxamate was efficiently arylated with diaryliodonium salts at room temperature under transition-metal-free conditions. The obtained O-arylated products were reacted in situ with ketones under acidic conditions to yield substituted benzo[b]furans through oxime formation, [3,3]-rearrangement, and cyclization in a fast and operationally simple one-pot fashion without using excess reagents. Alternatively, the O-arylated products could be isolated or transformed in situ to aryloxyamines or O-arylaldoximes. The methodology was applied to the synthesis of Stemofuran A and the formal syntheses of Coumestan, Eupomatenoid 6, and (+)-machaeriol B.

  • 2.
    Lindstedt, Erik
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Stridfeldt, Elin
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Olofsson, Berit
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Mild Synthesis of Sterically Congested Alkyl Aryl Ethers2016In: Organic Letters, ISSN 1523-7060, E-ISSN 1523-7052, Vol. 18, no 17, p. 4234-4237Article in journal (Refereed)
    Abstract [en]

    An efficient and transition-metal-free method is presented to access tertiary alkyl aryl ethers by arylation of tertiary alcohols with ortho-substituted diaryliodonium salts. The scope covers cyclic and acyclic aliphatic, benzylic, allylic, and propargylic tertiary alcohols as well as primary and secondary fluorinated alcohols. The methodology gives access to alkyl aryl ethers of previously unprecedented steric congestion. Furthermore, the versatility of the developed procedure was demonstrated by arylation of the pro-drug mestranol.

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  • 3.
    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.

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    Hypervalent Iodine Reagents in Metal-Free Arylations and Vinylations
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  • 4.
    Stridfeldt, Elin
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Metal‐Free Arylations of Oxygen and Nitrogen Nucleophiles: Applications of Diaryliodonium Salts2015Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis concerns development of new methods for metal‐free arylations in organic synthesis. The protocols discussed in the thesis are based on a class of hypervalent iodine compounds called diaryliodonium salts. These reagents are known to transfer aryl moieties to suitable nucleophiles.

    The first part describes O‐arylation of ethyl acetohydroxamate, which serves as a hydroxylamine equivalent. Electron‐rich as well as electron‐poor aryl groups could be transferred from the diaryliodonium salts. The arylation products could then be used as intermediates in a straightforward meta‐free one‐pot synthesis of benzofurans. Using this procedure, various substituted benzofurans were obtained in good yields. Furthermore, this methodology was used to synthesise the natural product Stemofuran A in one single step, starting from commercially available compounds. Three formal syntheses of other bioactive benzofurans were included.

    The second part describes N‐arylation of secondary acyclic amides. The chemoselectivity was explored with unsymmetric diaryliodonium salts, and aryl moieties with ortho‐substituents were preferably transferred. The protocol was suitable for electron‐deficient as well as highly sterically congested diaryliodonium salts. The transfer of electron‐rich aryl moieties was problematic. However, the reactivity for the amide was complementary to that of the salts and electron‐rich amides were phenylated in high yields. Furthermore, the protocol was compatible with benzamides and amides having sterically hindered acyl groups.

    Both arylation protocols discussed in this thesis work at ambient temperature and a variety of counter‐ions of the diaryliodonium salts were tolerated.

  • 5.
    Stridfeldt, Elin
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Lindstedt, Erik
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Reitti, Marcus
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Blid, Jan
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Norrby, Per-Ola
    Olofsson, Berit
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Competing Pathways in O-Arylations with Diaryliodonium Salts: Mechanistic Insights2017In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 23, no 53, p. 13249-13258Article in journal (Refereed)
    Abstract [en]

    A mechanistic study of arylations of aliphatic alcohols and hydroxide with diaryliodonium salts, to give alkyl aryl ethers and diaryl ethers, has been performed using experimental techniques and DFT calculations. Aryne intermediates have been trapped, and additives to avoid by-product formation originating from arynes have been found. An alcohol oxidation pathway was observed in parallel to arylation; this is suggested to proceed by an intramolecular mechanism. Product formation pathways via ligand coupling and arynes have been compared, and 4-coordinated transition states were found to be favored in reactions with alcohols. Furthermore, a novel, direct nucleophilic substitution pathway has been identified in reactions with electron-deficient diaryliodonium salts.

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  • 6.
    Stridfeldt, Elin
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Seemann, Alexandra
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bouma, Marinus J.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Dey, Chandan
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Ertan, Anne
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Olofsson, Berit
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Synthesis, Characterization and Unusual Reactivity of Vinylbenziodoxolones-Novel Hypervalent Iodine Reagents2016In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 22, no 45, p. 16066-16070Article in journal (Refereed)
    Abstract [en]

    A novel type of hypervalent iodine(III) reagents, vinylbenziodoxolones (VBX), has been synthesized in a one-pot reaction from 2-iodobenzoic acid. VBX is bench stable, has been thoroughly characterized and the cyclic structure is supported by X-ray analysis. The reactivity of VBX was investigated in vinylation of nitrocyclohexane, and delivered vinylated products with opposite regioselectivity compared to acyclic vinyl(aryl) iodonium salts. The reagents could become a powerful tool in vinylation reactions under both metal-free and metal-catalyzed conditions.

  • 7.
    Tinnis, Fredrik
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Stridfeldt, Elin
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Lundberg, Helena
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Adolfsson, Hans
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Olofsson, Berit
    Stockholm University, Faculty of Science, Department of Organic Chemistry. Stellenbosch University, South Africa.
    Metal-Free N-Arylation of Secondary Amides at Room Temperature2015In: Organic Letters, ISSN 1523-7060, E-ISSN 1523-7052, Vol. 17, no 11, p. 2688-2691Article in journal (Refereed)
    Abstract [en]

    The arylation of secondary acyclic amides has been achieved with diaryliodonium salts under mild and metal-free conditions. The methodology has a wide scope, allows synthesis of tertiary amides with highly congested aryl moieties, and avoids the regioselectivity problems observed in reactions with (diacetoxyiodo)benzene.

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