Asymmetric syntheses. Part VII. Asymmetric reduction of ketones and alk-2-en-4-yn-1-ols with a lithium bismenthyloxyaluminium hydride complex; determination of the absolute configurations of allenic alcohols

Abstract

(+)-Hexa- and (+)-hepta-3,4-dienols are readily obtained by reduction of hex- and hept-2-en-4-yn-1-ols with lithium bismenthyloxyaluminium hydride. Both dienols have been shown to have the (+)-S-configuration; this was confirmed by a synthesis of the former from (–)-(S)-α-chloroethyl 1-methylprop-2-ynyl ether involving elimination of hydrogen chloride followed by a Claisen sigmatropic rearrangement, and reduction of the resulting aldehyde. Asymmetric reduction of 4-methyl- and 4,4-dimethyl-pentan-2-ones with lithium bismenthyloxyaluminium hydride gave partially resolved (+)-4-methyl- and 4,4-dimethyl-pentan-2-ols.