Studies on the stereochemical control of fermenting baker's yeast mediated reductions: Some 3- and 4-oxo esters

Ethyl 4-benzyloxy-3-oxobutanoate (1c) is reduced by fermenting baker's yeast with stereochemical control which is dependent on the yeast:substrate ratio and the presence or absence of ethanol. Contrary to earlier reports, ethyl levulinate (3a) can be stereospecifically reduced to (+)-(S)-ethyl 4-hydroxypentanoate (4a) (15% yield, >95% optical purity) as shown by the conversion of (4a) into (-)-(S)-5-methyl-γ-valerolactone (5b). Also, ethyl 4-oxo-4-phenylbutanoate (3b) is stereospecifically reduced to the previously unreported (-)-(S)-5-phenyl-γ-butyrolactone (5c). The stereochemistry of compound (5c) has been established by chemical correlation with (-)-(S)-ethyl 3-hydroxy-3-phenylpropanoate (4c), which in turn was prepared by the baker's yeast reduction of ethyl 3-oxo-3-phenylpropanoate (3e).