Asymmetric Reduction of Various Types of Ketones with Lithium Aluminum Hydride partially decomposed with (-)-N-Methylephedrine and N-Ethylaniline

抄録

The asymmetric reduction of open chain enones to the corresponding optically active allylic alcohols was achieved in higher chemical (92-100%) and optical (78-98% e.e.) yields than those for cyclic enones (58-88% chemical and 34-58% optical yields). The observed high optical yields for optically active allylic alcohols can be explained on the assumption that, unlike cyclic enones in which the double bonds are fixed in s-trans conformation, open chain enones can be reduced in their s-cis conformations. An optically active propargylic alcohol was similarly produced from an ynone in 88% chemical and 76% optical yields by means of the present asymmetric reduction. When the same asymmetric reduction was applied to simple aromatic and aliphatic ketones by using 1.8 eq of the chiral reducing agent, the corresponding optically active alcohols were obtained in 88-100% chemical and 51-90% optical yields (for aromatic ketones) and in 78-98% chemical and 0-67% optical yields (for aliphatic ketones). On the basis of the results obtained in this and the preceding paper, a possible structure of the exploited chiral reducing agent is proposed and the transition states for the asymmetric reduction are discussed.