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Issue 21, 2003
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The complexity of catalysis: origins of enantio- and diastereocontrol in sulfur ylide mediated epoxidation reactions

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Abstract

The reaction of chiral sulfur ylides with aldehydes and ketones has emerged as a useful asymmetric process for the synthesis of epoxides. Processes employing either catalytic or stoichiometric amounts of sulfides have been developed. Although a large number of chiral sulfur ylides have been tested in the epoxidation process, only a few have delivered high diastereo- and enantio- selectivity. This review examines the factors that influence stereocontrol (steric hindrance of the sulfide, ylide conformation, ylide face selectivity, reversibility of betaine formation, solvent, and metal salts). This analysis leads to the conclusion that high reversibility in betaine formation leads to high diastereoselectivity but low enantioselectivity, and non-reversible betaine formation leads to low diastereoselectivity and high enantioselectivity (provided that other criteria are met). To achieve both high diastereoselectivity and high enantioselectivity simultaneously, requires non-reversible formation of the anti-betaine and reversible formation of the syn-betaine. Thus, factors that influence the degree of reversibility in betaine formation are critically important since with subtle changes in reaction conditions (solvent, temperature, metal ions) both high enantio- and diastereoselectivity can often be achieved.

Graphical abstract: The complexity of catalysis: origins of enantio- and diastereocontrol in sulfur ylide mediated epoxidation reactions

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Publication details

The article was received on 30 Apr 2003, accepted on 29 Jul 2003 and first published on 28 Aug 2003


Article type: Feature Article
DOI: 10.1039/B304625G
Citation: Chem. Commun., 2003,0, 2644-2651
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    The complexity of catalysis: origins of enantio- and diastereocontrol in sulfur ylide mediated epoxidation reactions

    V. K. Aggarwal and J. Richardson, Chem. Commun., 2003, 0, 2644
    DOI: 10.1039/B304625G

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