Metal-Free Ammonia Borane-Catalyzed Hydroboration of Lactones and Esters to Alcohols

Herein we describe an efficient methodology for metal-free hydroborative cleavage of lactones and esters with HBPin (Pin=pinacol) to the corresponding alcohol derivatives using ammonia borane as a pre-catalyst. The reactions proceed under mild conditions, can be performed in a solvent-free manner, and do not require an inert atmosphere. Combined experimental and computational mechanistic studies suggest a novel mechanism that involves μ-aminodiboranes as catalytically active species.