Regio- and enantioselective bioreduction of ethyl 2,4-dioxoalkanoates and γ-keto-α-enamino esters with fermenting bakers' yeast.

2,​4-​Dioxoalkanoates, e.g., AcCH2COCO2Me, and the parent γ-​keto-​α-​enamino esters, e.g., AcCH:C(NH2)​CO2Me, are regioselectively reduced by bakers' yeast to (R)​-​α-​hydroxy-​γ-​ketoesters (R)​-​RCOCH2CH(OH)​CO2R1 (R-​I; R, R1 = Me, Et, R = R1 = Me, Et)​, in moderate to good chem. yield and appreciable enantioselectivity. Enantioselective hydrolysis by pig liver esterase of the acetyl derivs., e.g., AcCH2CH(OAc)​CO2Me, easily obtained by acetylation of racemic α-​hydroxy-​γ-​keto esters I, produced the optically active (S)​-​I in good chem. (60-​92​%) and optical (53-​92​%) yield