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Thorsten Bach - One of the best experts on this subject based on the ideXlab platform.

  • iminium and enamine Catalysis in Enantioselective photochemical reactions
    Chemical Society Reviews, 2018
    Co-Authors: Youquan Zou, Fabian M Hormann, Thorsten Bach
    Abstract:

    Although Enantioselective Catalysis under thermal conditions has been well established over the last few decades, the Enantioselective Catalysis of photochemical reactions is still a challenging task resulting from the complex enantiotopic face differentiation in the photoexcited state. Recently, remarkable achievements have been reported by a synergistic combination of organoCatalysis and photoCatalysis, which have led to the expedient construction of a diverse range of enantioenriched molecules which are generally not easily accessible under thermal conditions. In this tutorial review, we summarize and highlight the most significant advances in iminium and enamine Catalysis of Enantioselective photochemical reactions, with an emphasis on catalytic modes and reaction types.

  • Enantioselective Catalysis of photochemical reactions.
    Angewandte Chemie (International ed. in English), 2015
    Co-Authors: Richard Brimioulle, Dominik Lenhart, Mark M. Maturi, Thorsten Bach
    Abstract:

    The nature of the excited state renders the development of chiral catalysts for Enantioselective photochemical reactions a considerable challenge. The absorption of a 400 nm photon corresponds to an energy uptake of approximately 300 kJ mol(-1) . Given the large distance to the ground state, innovative concepts are required to open reaction pathways that selectively lead to a single enantiomer of the desired product. This Review outlines the two major concepts of homogenously catalyzed Enantioselective processes. The first part deals with chiral photocatalysts, which intervene in the photochemical key step and induce an asymmetric induction in this step. In the second part, reactions are presented in which the photochemical excitation is mediated by an achiral photocatalyst and the transfer of chirality is ensured by a second chiral catalyst (dual Catalysis).

  • A Chiral Thioxanthone as an Organocatalyst for Enantioselective [2+2] Photocycloaddition Reactions Induced by Visible Light
    Angewandte Chemie (International ed. in English), 2014
    Co-Authors: Rafael Alonso, Thorsten Bach
    Abstract:

    Thioxanthone 1, which was synthesized in a concise fashion from methyl thiosalicylate, exhibits a significant absorption in the visible light region. It allows for an efficient Enantioselective Catalysis of intramolecular [2+2] photocycloaddition reactions presumably by triplet energy transfer.

Henri Brunner - One of the best experts on this subject based on the ideXlab platform.

  • Asymmetric Catalysis, 154 [1]. New 1,1’-Binaphthyl Ligands for Enantioselective Catalysis
    Zeitschrift für Naturforschung B, 2003
    Co-Authors: Henri Brunner, Matthias Weber, Manfred Zabel
    Abstract:

    Chiral binaphthyl compounds, especially those with different substituents in 2- and 2'-position of the binaphthyl system, have gained interest as constituents of successful ligands in various catalytic reactions. Here, wepresent the synthesis and characterization of new binaphthyl ligands containing oxazoline, cyano and amide substituents in 2'-position in addition to methoxy, hydroxy or amino groups in 2-position. Starting from these compounds new ligands for Enantioselective Catalysis will be accessible.

  • Narcotic drug methohexital: synthesis by Enantioselective Catalysis.
    Chirality, 2001
    Co-Authors: Henri Brunner
    Abstract:

    The narcotic drug methohexital 1 contains two asymmetric carbon atoms and, thus, consists of four isomers, two diastereomeric pairs of enantiomers. The commercial drug is the so-called alpha-racemate, one pair of diastereomers only. A method was developed to prepare differently enriched mixtures of methohexital isomers without resorting to lengthy and expensive optical resolutions. A model reaction for the synthesis of methohexital is the palladium-catalyzed allylation of 1,5-dimethyl-barbituric acid 3, which is optimized and checked by molecular modeling. Catalysts with the best ligands are used in the allylation of the methohexital precursor 7, which contains the C(6) sidechain at the tetrahedral center of the barbiturate skeleton. The product stereochemistry was determined by the contribution of the Enantioselective Pd catalysts and by the fact that the allylation is a kinetic resolution. The methohexital isomer mixtures obtained were evaluated with the corneal stimulus test of rats. Methohexital compositions were found, which are superior to the commercially used alpha-racemate (Brevimytal).

  • Enantioselective Catalysis: Part 129. A new rhodium(I) complex with a μ2-H bridged Cp2WH2 ligand☆
    Journal of Organometallic Chemistry, 1999
    Co-Authors: Henri Brunner, Darijo Mijolovic
    Abstract:

    Abstract The optically active complex {[(−)-diop]Rh(μ 2 -H) 2 WCp 2 }PF 6 was prepared and characterized. In four different models of Enantioselective Catalysis the complex gave the same enantioselectivity as the catalysts [Rh(cod)Cl] 2 /(−)-diop and [Rh(cod)Cl] 2 /(−)-diop/Cp 2 WH 2 .

  • Enantioselective Catalysis; 130: Optically Active Expanded Ligands Based on the trans-1,2-Substituted Cyclopentane Skeleton
    Synthesis, 1999
    Co-Authors: Henri Brunner, Stefan Stefaniak, Manfred Zabel
    Abstract:

    New expanded bisphosphane ligands with a chiral trans-1,2-substituted cyclopentane skeleton were prepared. Polyaldehydes were accessible by coupling optically active bisphosphane precursors with branched aryl bromides. Optically active expanded ligands were obtained by condensation of the aldehydes with chiral amines and amino alcohols. The optically active ligands were tested in several model reactions of Enantioselective Catalysis, including allylic alkylation, hydrogenation (adopted to the use of water), and hydrosilylation.

  • Homogeneous Enantioselective Catalysis
    Chiral Reactions in Heterogeneous Catalysis, 1995
    Co-Authors: Henri Brunner
    Abstract:

    The intention of the lecture on homogeneous Enantioselective Catalysis in the ChiCat Conference on heterogeneous Enantioselective Catalysis was to work out the differences between homogeneous and heterogeneous Enantioselective Catalysis and to show the contributions of homogeneous Catalysis to the understanding of a catalyst'S enantioselectivity.

Thomas R Ward - One of the best experts on this subject based on the ideXlab platform.

  • artificial metalloenzymes based on the biotin avidin technology Enantioselective Catalysis and beyond
    Accounts of Chemical Research, 2011
    Co-Authors: Thomas R Ward
    Abstract:

    Artificial metalloenzymes are created by incorporating an organometallic catalyst within a host protein. The resulting hybrid can thus provide access to the best features of two distinct, and often complementary, systems: homogeneous and enzymatic catalysts. The coenzyme may be positioned with covalent, dative, or supramolecular anchoring strategies. Although initial reports date to the late 1970s, artificial metalloenzymes for Enantioselective Catalysis have gained significant momentum only in the past decade, with the aim of complementing homogeneous, enzymatic, heterogeneous, and organic catalysts. Inspired by a visionary report by Wilson and Whitesides in 1978, we have exploited the potential of biotin−avidin technology in creating artificial metalloenzymes. Owing to the remarkable affinity of biotin for either avidin or streptavidin, covalent linking of a biotin anchor to a catalyst precursor ensures that, upon stoichiometric addition of (strept)avidin, the metal moiety is quantitatively incorporated...

  • artificial metalloenzymes for Enantioselective Catalysis recent advances
    ChemBioChem, 2006
    Co-Authors: Christophe Letondor, Thomas R Ward
    Abstract:

    Creating new catalytic function in proteins. Anchoring an organometallic moiety within a protein affords artificial metalloenzymes for Enantioselective Catalysis. Both chemical and genetic tools can be applied in the optimization of such systems, which lie at the interface between homogeneous and enzymatic Catalysis. This minireview presents the latest developments in the field of artificial metalloenzymes.

  • Artificial metalloenzymes: proteins as hosts for Enantioselective Catalysis
    Chemical Society reviews, 2005
    Co-Authors: Christophe M. Thomas, Thomas R Ward
    Abstract:

    Enantioselective Catalysis is one of the most efficient ways to synthesize high-added-value enantiomerically pure organic compounds. As the subtle details which govern enantioselection cannot be reliably predicted or computed, Catalysis relies more and more on a combinatorial approach. BioCatalysis offers an attractive, and often complementary, alternative for the synthesis of enantiopure products. From a combinatorial perspective, the potential of directed evolution techniques in optimizing an enzyme's selectivity is unrivaled. In this review, attention is focused on the construction of artificial metalloenzymes for Enantioselective catalytic applications. Such systems are shown to combine properties of both homogeneous and enzymatic kingdoms. This review also includes our recent research results and implications in the development of new semisynthetic metalloproteins for the Enantioselective hydrogenation of N-protected dehydro-amino acids.

  • Exploiting the second coordination sphere : proteins as host for Enantioselective Catalysis
    CHIMIA International Journal for Chemistry, 2003
    Co-Authors: Thomas R Ward, Christophe Letondor, Jerome Collot, Julieta Gradinaru, Andreas Loosli, Myriem Skander, Edith Joseph, Gérard Klein
    Abstract:

    With the aim of exploring the role of the second coordination sphere in Enantioselective Catalysis, achiral organometallic catalyst precursors are anchored in proteins via non-covalent interactions. A chemogenetic procedure allows the activity and the enantioselectivity of the artificial metalloenzymes to be optimized, to yield hybrid catalysts with features reminiscent both of enzymatic and homogeneous catalysts.

  • Efficient expression and mutation of avidin and streptavidin as host proteins for Enantioselective Catalysis
    CHIMIA International Journal for Chemistry, 2003
    Co-Authors: Andrea Zocchi, Nicolas Humbert, Temugin Berta, Thomas R Ward
    Abstract:

    Avidin and structurally related streptavidin are attractive host proteins for the creation of artificial metalloenzymes displaying features reminiscent both of homogeneous catalysts and enzymes. The main advantages are that both proteins have been cloned and expressed in several organisms and possess a deep hydrophobic binding pocket capable of hosting biotinylated catalyst precursors. An optimized artificial avidin gene in Pichia pastoris is expressed. The high level of active protein produced in the extracellular medium is suitable for the performance of high-throughput screening in 96-well plate format. Biologically active recombinant streptavidin is expressed in E. coli. Mutations have been introduced both in avidin and streptavidin genes and both wild type and mutated proteins have been utilized to explore the role of the second coordination sphere in Enantioselective Catalysis.

Lutz H. Gade - One of the best experts on this subject based on the ideXlab platform.

Wenbin Lin - One of the best experts on this subject based on the ideXlab platform.

  • Enantioselective Catalysis with homochiral metal–organic frameworks
    Chemical Society Reviews, 2009
    Co-Authors: Liqing Ma, Carter Abney, Wenbin Lin
    Abstract:

    This tutorial review presents recent developments of homochiral metal-organic frameworks (MOFs) in Enantioselective Catalysis. Following a brief introduction of the basic concepts and potential virtues of MOFs in Catalysis, we summarize three distinct strategies that have been utilized to synthesize homochiral MOFs. Framework stability and accessibility of the open channels to reagents are then addressed. We. finally survey recent successful examples of catalytically active homochiral MOFs based on three approaches, namely, homochiral MOFs with achiral catalytic sites, incorporation of asymmetric catalysts directly into the framework, and post-synthetic modification of homochiral MOFs. Although still in their infancy, homochiral MOFs have clearly demonstrated their utility in heterogeneous asymmetric Catalysis, and a bright future is foreseen for the development of practically useful homochiral MOFs in the production of optically pure organic molecules.

  • Enantioselective Catalysis with homochiral metal organic frameworks
    Chemical Society Reviews, 2009
    Co-Authors: Carter W Abney, Wenbin Lin
    Abstract:

    This tutorial review presents recent developments of homochiral metal–organic frameworks (MOFs) in Enantioselective Catalysis. Following a brief introduction of the basic concepts and potential virtues of MOFs in Catalysis, we summarize three distinct strategies that have been utilized to synthesize homochiral MOFs. Framework stability and accessibility of the open channels to reagents are then addressed. We finally survey recent successful examples of catalytically active homochiral MOFs based on three approaches, namely, homochiral MOFs with achiral catalytic sites, incorporation of asymmetric catalysts directly into the framework, and post-synthetic modification of homochiral MOFs. Although still in their infancy, homochiral MOFs have clearly demonstrated their utility in heterogeneous asymmetric Catalysis, and a bright future is foreseen for the development of practically useful homochiral MOFs in the production of optically pure organic molecules.