Aldol Process Catalyzed by Chiral Tin Methoxides

Significance

The importance of the catalytic asymmetric aldol reaction can hardly be overestimated. Among numerous existing methods there are, however, few examples of enantioselective aldol reaction proceeding via a chiral metal enolate. The authors previously found that Bu₂Sn(OMe)₂ catalyzes the reaction between alkenyl trichloroacetates and aldehydes in the presence of methanol. In this paper they expand this methodology to a chiral version using chiral tin methoxide formed in situ from dibromide 2. The use of 10 mol% of catalyst furnished a number of acyclic products with yields of 41-80% and high enantioselectivities (88-99%). The diastereoselectivity ranged from 85:15 to >99:1. A number of cyclic substrates were also employed with moderate success.