Regio- and Enantioselective Epoxidation of Dienes by a Chiral Dioxirane: Synthesis of Optically Active Vinyl c/s-Epoxides

摘要

Optically active vinyl epoxides are very useful synthetic intermediates, and enantioselective monoepoxidation of conjugated dienes presents an efficient approach to these compounds. Enantioselective epoxidation of conjugated dienes using chiral (salen)Mn catalysts has been shown to proceed predominantly at the cis-olefin with high regioselec-tivity and high enantioselectivity. In the case of acyclic dienes, the epoxidation gave optically active vinyl trans-epoxides as major products. Earlier, we reported that fructose-derived ketone 1 (Scheme 1) is effective for the regioselective epoxidation of conjugated dienes to provide vinyl trans- and trisubstituted epoxides with high ee values [Eq. (1)] , Nevertheless, an efficient synthesis of chiral vinyl cw-epoxides is still highly desirable.