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Asymmetric Transformation (asymmetric + transformation)

Distribution by Scientific Domains
Chemistry100%

Kinds of Asymmetric Transformation

  • kinetic asymmetric transformation
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    Selected Abstracts

    Copper-Catalyzed Asymmetric Allylic Alkylation of Racemic Cyclic Substrates: Application of Dynamic Kinetic Asymmetric Transformation (DYKAT)

    ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 2-3 2010
    Jean-Baptiste Langlois
    Abstract The copper-catalyzed asymmetric allylic alkylation (AAA) is of great interest in organic synthesis. This reaction was extensively studied using a broad range of substrates, ligands and organometallic reagents. However, the use of racemic substrates was still limited. Although some processes of kinetic resolution are reported in the literature, no examples of quantitative deracemization are described as is the case for the Pd-catalyzed allylic alkylation. We present here a full account of our investigations through the development of the first example of such a process in copper-catalyzed AAA. High enantioselectivities (up to 99% ee), scope of the reaction and mechanistic considerations are reported herein. [source]

    A Practical Improvement of Crystallization-Induced Asymmetric Transformation of Allene-1,3-dicarboxylates.

    CHEMINFORM, Issue 14 2007
    Takahiro Katoh
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source]

    Titanium(IV)-Catalyzed Dynamic Kinetic Asymmetric Transformation of Alcohols, Silyl Ethers, and Acetals under Carbon Allylation.

    CHEMINFORM, Issue 21 2004
    Manfred Braun
    Abstract For Abstract see ChemInform Abstract in Full Text. [source]

    Highly Efficient Synthesis of Enantiopure Diacetylated C2 -Symmetric Diols by Ruthenium- and Enzyme-Catalyzed Dynamic Kinetic Asymmetric Transformation (DYKAT)

    CHEMISTRY - A EUROPEAN JOURNAL, Issue 23 2006
    Belén Martín-Matute Dr.
    Abstract Highly efficient synthesis of enantiopure diacetates of 2,4-pentanediol and 2,5-hexanediol starting from commercially available mixtures of the diols (dl/meso ,1:1) has been realized by combining a fast ruthenium-catalyzed epimerization with an enzymatic transesterification. The in situ coupling of these two processes produces the diacetates in high yield in >99,% enantiomeric excess. [source]

    Oxidoreductases Working Together: Concurrent Obtaining of Valuable Derivatives by Employing the PIKAT Method

    CHEMCATCHEM, Issue 8 2010
    Fabricio
    Flying PIKATs: The stereoselective oxidation of several sulfides linked to the enantioselective oxidation of different sec -alcohols are combined in a parallel interconnected kinetic asymmetric transformation (PIKAT) fashion. Furthermore, the cofactor concentration employed in these processes is investigated, demonstrating a high capacity of performance, even at micromolar concentrations of the mediator. [source]

    Planar-Chiral Thioureas as Hydrogen-Bond Catalysts

    EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 12 2010
    Jakob F. Schneider
    Abstract The synthesis of the first enantiopure planar-chiral thiourea catalysts is herewith described. New catalysts 1,3 were applied in asymmetric transformations, such as the Friedel,Crafts alkylation of indole, as well as in the transfer hydrogenation of nitroolefins. Bifunctional catalysts 2 and 3 exhibit enhanced activity in the investigated reactions, demonstrating their potential for organic synthesis. [source]

    Remarkable Efficiency Improvement in the Preparation of Insoluble Polymer-Bound (IPB) Enantioselective Catalytic Systems by the Use of Silicone Chemistry

    ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 3 2008
    Alessandro Mandoli
    Abstract The use of platinum-catalyzed hydrosilylation chemistry of silicones greatly simplifies the preparation of bis-oxazoline (box) ligands covalently bound to an insoluble polymeric support. The use of such immobilized chiral ligands in different copper-catalyzed asymmetric transformations (carbonyl-ene, Mukaiyama aldol and olefin cyclopropanation reactions) allows the attainment of high levels of enantioselectivity (91,99,% ee). [source]

    Organocatalysis Mediated by (Thio)urea Derivatives

    CHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2006
    Stephen J. Connon Dr.
    Abstract Over the last decade the potential for N,N -dialkyl(thio)urea derivatives to serve as active metal-free organocatalysts for a wide range of synthetically useful reactions susceptible to the influence of general acid catalysis has begun to be realised. This article charts the development of these catalysts (with emphasis on the design principles involved), from early "proof-of-concept" materials to contemporary active chiral (bifunctional) promoters of highly selective asymmetric transformations. [source]

    Asymmetric catalysis by chiral lanthanide complexes in water

    CHIRALITY, Issue 7 2005
    Rachel S. Dickins
    Abstract The development of catalytic, asymmetric transformations in water is a challenging task. The lanthanides are becoming reagents of choice for many Lewis acid-catalyzed reactions in aqueous media as they are water tolerant. However, enantioselective reactions catalyzed by lanthanides are difficult to achieve in water due to the instability of the reported catalysts. Herein we report the development of stable, well-defined chiral lanthanide complexes and their effectiveness in the asymmetric reduction of ,-keto acids in aqueous solution. This is the first example of asymmetric reduction by a chiral lanthanide complex in water. Although modest ees are obtained (40,50%) the ytterbium complexes offer a unique advantage as they have the ability to monitor, direct from the reaction mixture, the % ee for the reaction, by 1H NMR, through a dipolar analysis of the observed paramagnetic shift. Chirality 17:357,363, 2005. © 2005 Wiley-Liss, Inc. [source]