The Cyanohydridoborate Anion as a Selective Reducing Agent

Abstract

Sodium cyanohydridoborate (NaBH3CN) reduces a wide variety of organic functional groups with remarkable selectivity. The reduction of aldehydes and ketones is pH dependent, the reaction proceeding readily at pH 3-4. Oximes are smoothly reduced to alkylhydroxylamines and enamines are reduced to amines under acid catalysis. Reaction of an aldehyde or ketone with ammonia, primary amine, or secondary amine at pH -7 in the presence of BHaCN- leads to primary, secondary, or tertiary amines, respectively, uia reductive amination of the carbonyl group. Reaction of substituted pyruvic acids with ammonia and BH3CN- affords an excellent method for the synthesis of amino acids; l5N labeling can be accomplished by using I5NH3. The hydrogens of BHICNcan be readily exchanged for either deuterium or tritium, thus permitting the synthesis of deuterium- or tritiumlabeled alcohols, amines, and amino acids