Catalyst- and Additive-Free Reduction of Carboxylic Acids and Amides Using Ammonia Borane as Hydrogen Source

Abstract

The study reports an economical synthetic protocol employing air-stable NH3·BH3 as an H2 equivalent for the catalyst- and additive-free reduction of both aliphatic and aromatic carboxylic acids, offering a series of structurally diverse corresponding primary alcohols. The designed system has been reported to selectively reduce secondary and tertiary amides into amines, providing moderate to high production yield. The reaction is readily scalable, highly selective, and tolerant of sensitive functional groups, such as bromine, chlorine, fluorine, iodine, nitro, and cyano groups. Mechanistic investigations demonstrated a stepwise hydride-transfer pathway proceeding through a 6-membered cyclic transition state, with aldehyde and imine species as key intermediates, respectively. The proposed operationally simple, metal-free strategy offers a practical and economical route for the production of valuable alcohol and amine building blocks.