On the reduction of enol acetates and enolates derived from α-chiral ketones with lithium tetrahydridoaluminate

Abstract

The Z- and E-isomers of 1-acetoxy-1,2-diphenylprop-1-ene (1) and (2), and of 3-acetoxy-4,4-dimethyl-2-phenylpent-2-ene (3) and (4), have been converted into their respective alcohols (1RR,2SS)- and (1RS,2SR)-1,2-diphenylpropan-1-ol (5) and (6), and (1RR,2SS)- and (1RS,2SR)-2,2-dimethyl-4-phenylpentan-3-ol (7) and (8), by treatment with lithium tetrahydridoaluminate in different solvents (diethyl ether, tetrahydrofuran, 1,2-dimethoxyethane, triethylamine, and 1,4-dioxane). Deuteriolysis of the reaction mixture yields, almost quantitatively, the β-deuteriated products and, in every case, the reaction is completely stereoselective in the (RR,SS)-alcohol. Form these results and the observation of the stereochemistry and conversion during the reaction, a mechanism is proposed. This includes a metallated ketone as a chiral intermediate in the reduction process.