Reduction of parochial ketones with optically active borohydride reagents

ABSTRACT

The phenomenon of asymmetric induction in the synthesis of compounds that already contain one or more asymmetric carbon atoms has been recognized for many years, the classic work in a cyclic system being that of McKenzie. Many types of asymmetric synthesis have been reported in which prochiral ketones have been reduced to optically active alcohols utilizing optically active reducing agents. Many studies mostly based on the use of lithium aluminium hydride [LAH] modified by chiral alcohols, amino alcohols and amines have been conducted altering both the reagents and the experimental conditions to obtain an optimum fit and to gain an insight into the mechanism of reduction. On the other hand, a few studies on the use of sodium borohydride [NaBH4] in the same type of asymmetric reduction have been reported. In the last few years, growing attention has been devoted to asymmetric synthesis under phase transfer condition. Recently, interesting results have been obtained by Sugimoto et al. in the asymmetric reduction of aromatic ketones with NaBH[4] in the presence of bovine serum albumin in alkaline solution. Accordingly, we were interested in the present investigations to study the asymmetric reduction of ketones with chirally modified reagents prepared from NaBH[4] and optically active acids