Enantioselective Selenium and Tellurium Ylide Catalysis

Achiral tellurides were used in the catalytic epoxidation of aldehydes by Huang and coworkers in 1990. With diisobutyl telluride as a catalyst (20mol%), various aromatic, heteroaromatic, and non-primary aliphatic aldehydes can be epoxidized directly with aUyhc bromide to the corresponding vinyl epoxides in good yields with predominantly cis-selectivity [59], Later, they successfully extended this method to the cyclopropanation of a,(3-unsaturated ketones with aUyl bromides [60], The asymmetric version of the cyclopropanation was realized by Tang and coworkers in 2003 [61], using salt 43 directly as a catalyst (20mol%) in the reaction of chalcones with silylated aUyl bromide. The desired vinyl cyclopropanes were 

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 

3 (a) Berkessel, A. and Groeger, H. (eds) (2005) Asymmetric Organocatalysis, Wiley-VCH Verlag GmbH, Weinheim  

32 (a) Katsuki, T. (1999) Comprehensive Organic Catalysis, vol. 2 (eds E.N. Jacobsen, A. Pfaltz, and H. Yamamoto), Springer-Verlag, Berlin, pp. 621 48 (b) Jacobsen, E.N. andWu, M.H. (1999) Comprehensive Asymmetric Catalysis, vol. 2 (eds E.N. Jacobsen, A. Pfaltz, and H. Yamamoto), Springer-Verlag, Berlin, pp. 

Tuning Catalyst Activity and Selectivity by the Reaction Medium and Conditions 

58 (a) Takada, H., Metzner, P., and Philouze, C. (2001) Chem. Commun., 2350-2351 (b) Briere, J.F., Takada, H and Metzner, P. (2005) Phosphorus Sulfur Silicon Relat. Elem., 180,965-968. 

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