Asymmetric synthesis using chiral acetals: Studies on the nucleophilic addition of organometallics to chiral x-keto acetals in cyclic systems.

Abstract

Four chiral cyclic a-keto acetals (3a-d) were prepared through transacetalization of the α-hydroxydimethyl acetals [1 (n = 1, n = 2)] with (-) - (2S, 3S) -1, 4-dimethoxy-2, 3-butanediol or (-) - (2R, 3R) -2, 3-butanediol and reacted with organometallic reagents (Grignard reagents and organo-lithium reagents). The reactions of the α-keto acetals (3a, 3b) derived from 1 and (-) - (2S, 3S) -1, 4-dimethoxy-2, 3-butanediol with Grignard reagents proceeded in a highly diastereoselective manner.