Highly enantioselective reduction of ethyl 4-chloro-3-oxobutanoate to L-and D-3-hydroxyesters with baker`s yeast

Reduction with baker's yeast of ethyl or methyl 4-chloro-3-oxobutanoate in the presence of allyl bromide or allyl alcohol as additive afforded the corresponding L- and D-3-hydroxyesters. Several reduction conditions were tested, involving: different concentrations of additive; variations in the yeast/substrate ratio; the presence and absence of glucose; different pre-incubation periods; a range of temperatures. The best conditions gave a complete conversion of the substrate within 1-2 h and a very high enantioselectivity, 90-97% e.e., for the two enantiomers.