A New Reduction of Some Carboxylic Esters with Sodium Borohydride and Zinc Chloride in the Presence of a Tertiary Amine

Abstract In the presence of a tertiary amine, sodium borohydride (NaBH4) combined with zinc chloride (ZnCl2) showed powerful reducing properties and carboxylic esters were smoothly reduced to their corresponding alcohols which were not obtained by reduction with NaBH4 and ZnCl2 alone. Tetrahydrofuran (THF) was an efficient solvent, and the effective molar ratio of the reducing agents, NaBH4 : ZnCl2 : tertiary amine, was 2 : 1 : 1. In particular, aminobenzoates such as anthranilic esters, were reduced to aminobenzyl alcohols with high yields without the addition of a tertiary amine. Further, it was also found that this combination reduced nitro, cyano, and amido groups to their corresponding amino groups.