Chemoselective reductions with sodium borohydride

Abstract

Under the appropriate reaction conditions, sodium borohydride is a highly chemoselective reducing agent. The order of reactivity among carbonyl groups is conjugated enones < ketones < conjugated aldehydes < aldehydes. In general, a carbonyl group of one type can be selectively reduced in the presence of a carbonyl group of a less reactive type. Reactions are conducted with excess sodium borohydride at −78 °C in solvent mixtures of methanol or ethanol in dichloromethane. Keywords: sodium borohydride, chemoselective reductions.