Catalyst- and additive-free reduction of carboxylic acids and amides using ammonia borane as a hydrogen source

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 to amines, providing moderate to high product yields. 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.