The bioreduction of alpha -methyleneketones. (RC)-C-1(-O)C(-CH2)R-2 (R-1= Me, Et, Pr, iso-Bu, Ph. CH2CH2Ph: R-2 =Cl, Me, Et, n-Pr, iso-Pr. n-Bu, n-C6H13, Ph, CH2Ph), was mediated by baker's yeast (Saccharomyees cerevisiae) to obtain the corresponding alpha -methylkelones. The R-1 and R-2 groups had a significant influence on the rate and enantioselectivity of the reductions. The rate or C-C bond reduction was higher than that of C-O bond reduction. Only alpha -methyleneketones having R-1 = Me yielded alpha -methylketones in high enantioselectivity with e.e.s of 88-99%. (C) 2001 Elsevier Science Ltd, All rights reserved.126847852