STEREOSELECTIVE REDUCTION OF PROCHIRAL KETONES, USING ALUMINUM-HYDRIDE REAGENTS PREPARED FROM LIALH4 AND CHIRAL DIETHANOLAMINES

The asymmetric reduction of prochiral ketones to chiral secondary alcohols by LiAlH4, modified with optically active diethanolamines, was studied. Asymmetric inductions of up to 94% were obtained with these reagents. The stereoselectivity of the reaction was found to depend both upon the temperature at which the reduction was performed and upon the conditions under which the chiral aluminum hydride reagent had been prepared. By changing the substituents at the carbon atom alpha to nitrogen in the chiral auxiliary, either the (R)- or the (S)-enantiomer of the secondary alcohol could be obtained in excess.