Catalytic Asymmetric Darzens-Type Epoxidation of Diazoesters: Highly Enantioselective Synthesis of Trisubstituted Epoxides

摘要

Highly enantioselective Darzens-type epoxidation of diazoesters with glyoxal derivatives was accomplished using a chiral boron-Lewis acid catalyst, which facilitated asymmetric synthesis of trisubstituted alpha,beta-epoxy esters. In the presence of a chiral oxazaborolidinium ion catalyst, the reaction proceeded in high yield (up to 99 %) with excellent enantio- and diastereoselectivity (up to >99 % ee and >20:1 dr, respectively). The synthetic potential of this method was illustrated by conversion of the products to various compounds such as epoxy gamma-butyrolactone, tertiary beta-hydroxy ketone and epoxy diester.