Enantioselective ylide catalysis

Enantioselective Suljur Ylide Catalysis SS3 Table 20.1 Enantioselective epoxidation of aldehydes with sulfide 13. 

The sulfide-catalyzed enantioselective epoxidation reaction is the most extensively studied transformation in ylide catalysis, and two ylide generation methods (aUcylation/deprotonation and carbene transfer) have been developed. Compared with conventional methods for epoxidation via oxygen transfer to the carbon-carbon double bond, such as the Sharpless epoxidation, Jacobsen-Katsuki epoxidation, and Shi epoxidation, the yhde approach can be regarded as an alkyUdene transfer reaction to carbonyl groups (C=0), providing a different retrosynthetic analysis for the construction of epoxides. In particular, in the synthesis of vinyl epoxides, the ylide route has priority over conventional oxidation methods, since the issue of regjoselectivity in the epoxidation of dienes will not be present [32]. 

Highly enantioselective ylide-type covalent catalysis has been achieved with sulfides, phosphines, tertiary amines, selenides, and teUurides, and the reported reaction types include epoxidation, aziridination, cyclopropanation, and other cyclization reactions. So far, the sulfur ylide-mediated reactions are the best... 

One of the major goals set for tandem ylide formation-cycloaddition chemistry has been the application of enantioselective catalysis to form one product in preference to all others. It appears that these transformations must involve a catalyst associated ylide for some degree of enantioselectivity to occur. Generally, if the free ylide forms without any catalyst association then enantioselectivity is highly unlikely. 

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