ENANTIOSELECTIVE REDUCTION OF SOME AROMATIC KETONES BY BAKERS-YEAST

The reduction of aromatic ketones 1-6 by baker's yeast showed that acceptability of the substrates is not governed either by the number of aryl groups or by the distance of the carbonyl group from the aryl moiety. Relative rates of conversion of 3, 4, and 6 vs. ethyl acetoacetate as the "standard" substrate were reproducible in the order 3 > 6 > 4. Strong inhibition of reduction of ethyl acetoacetate by benzene vanished at very low concentrations of both. Reduction of phenyl-pyrid-2'yl-methyl ketone (1) and its deazaanalogue (6) gave the chiral sec. alcohols of the opposite configuration. (-)-7 and (+)-12, respectively. This could be ascribed to the prevalent binding of enol 1A by the opposite enantioface, as compared to 6. Absolute configuration of (-)-7 is tentatively assigned as R by the empirical rule based on the 1NMR spectra of Mosher's acid esters 13-15. This assignment is confirmed by the single crystal X-ray structure determination of camphanic acid ester 16A, which on hydrolysis affords (-)-7.