Reduction of Carboxylic Acid Derivatives by BH4(1-) in Acidic Dimethyl Sulfoxide

Article abstract of DOI:10.1021/jo00325a029

Carboxylic acid amides of all degrees of substitution, both aliphatic and aromatic, can be reduced to the corresponding primary, secondary or tertiary amines in good yield by a combination of NaBH4 and CH3SO2OH in dimethyl sulfoxide.The procedure also reduces aliphatic carboxylic acids and their esters to primary alcohols, but not conjugated aromatic acids.Crotonic acid is readily reduced to butanol.Isolated double bonds and nitriles also react, but the major products are not those of simple reduction.Michler's ketone is reduced to4,4'-bis(dimethylamino)diphenylmethane.The acid probably facilitates the amide reduction by protonating the carbonyl oxygen.The mechanism of the other reductions is less clear.The method does not require an anhydrous solvent, does not involve a hazardous reagent, has somewhat different selectivity than techniques in general use, and may sometimes be the method of choice.