Effects of Neighboring Functional Groups in the Asymmetric Reduction of ω-Substituted Alkyl Phenyl Ketones with Lithium Tri-<i>l</i>-Menthoxyaluminum Hydride

Abstract

Abstract In the enantioselective reduction of ω-substituted alkyl phenyl ketones, PhCO(CH2)nY, with lithium tri-l-menthoxyaluminum hydride, the effect of the functional groups, Y(NR2, OMe, and SMe) on the stereoselectivity was examined in comparison with that of the alkyl group. Of the functional groups tested, the MeO group is more effective in enhancing the stereoselectivity than the NMe2 or SMe group except in the case of n=1. The optical yields are also affected by the number of the methylene group (n) in the substrates. These results strongly suggest that the coordination of the Y group with the reducing reagent is one of the essential factors in the stereoselectivity. The absolute configurations of the resulting alcohols are correlated with the relative magnitudes of the lanthanideinduced shifts(LIS) of their (+)-MTPA esters.