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  • 1.
    Bah, Juho
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Naidu, Veluru Ramesh
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Teske, Johannes
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Franzén, Johan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Carbocations as Lewis Acid Catalysts: Scope and Reactivity2015In: Advanced Synthesis and Catalysis, ISSN 1615-4150, E-ISSN 1615-4169, Vol. 357, no 1, p. 148-158Article in journal (Refereed)
    Abstract [en]

    One class of potential Lewis acids that has received negligible attention as a catalyst is the carbocation. Here we show the potential of triarylmethylium ions as highly powerful Lewis acid catalysts for organic reactions. The Lewis acidity of the triarylmethylium ion can be easily tuned by variation of the electronic properties of the aromatic rings and the catalytic activity of the carbocation is shown to correlate directly to the level of stabilization of the empty p(C)-orbital at the cationic carbon. The versatility of triarylmethylium ions as efficient Lewis acid catalysts for organic reactions is demonstrated in Diels-Alder, aza-Diels-Alder, conjugate addition, halogenation, epoxide rearrangement and intramolecular hetro-ene reactions.

  • 2. Franzen, Johan.
    et al.
    Marigo, M.
    Fielenbach, D.
    Wabnitz, T. C.
    Kjaersgaard, A.
    Jorgensen, K. A.
    A general organocatalyst for direct alpha-functionalization of aldehydes: Stereoselective C-C, C-N, C-F, C-BR, and C-S bond-forming reactions. Scope and mechanistic insights2005In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 127, no 51, p. 18296-18304Article in journal (Refereed)
    Abstract [en]

    The development of a general organocatalyst for the alpha-functionalization of aldehydes, via an enamine intermediate, is presented. Based on optically active alpha,alpha-diarylprolinol silyl ethers, the scope and applications of this catalyst for the stereogenic formation of C-C, C-N, C-F, C-Br, and C-S bonds are outlined. The reactions all proceed in good to high yields and with excellent enantioselectivities. Furthermore, we will present mechanistic insight into the reaction course applying nonlinear effect studies, kinetic resolution, and computational investigations leading to an understanding of the properties of the alpha,alpha-diarylprolinol silyl ether catalysts.

  • 3.
    Franzén, Johan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Asymmetric Domino Reactions2013In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 52, no 47, p. 12222-12222Article, book review (Other academic)
  • 4.
    Ni, Shengjun
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Naidu, Veluru Ramesh
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Franzen, Johan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Chiral Anion Directed Asymmetric Carbocation-Catalyzed Diels-Alder Reactions2016In: European Journal of Organic Chemistry, ISSN 1434-193X, E-ISSN 1099-0690, no 9, p. 1708-1713Article in journal (Refereed)
    Abstract [en]

    In recent years the carbocation has re-emerged as a highly efficient Lewis acid catalyst for a variety of organic transformations. However, the goal of asymmetric carbocation catalysis has so far been out of reach mainly as a result of difficulties associated with the preparation of stable chiral carbocations. Here, we describe developments towards asymmetric carbocation catalysis based on the concept of chiral-anion-directed catalysis. Chiral tritylium salts can be conveniently prepared in situ by mixing trityl chloride derivatives with chiral phosphonate, phosphoramide, bis(sulfonyl) amide, and bis(sulfuryl) amide silver or sodium salts. It is shown that the bis(sulfuryl) amide/tritylium ion salt catalyzes the Diels-Alder reaction with an up to 53 % enantiomeric excess.

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