Chiral phosphoric acid catalyzed asymmetric transfer hydrogenation of bulky aryl ketones with ammonia borane

Abstract

An asymmetric transfer hydrogenation of bulky aryl ketones with ammonia borane was successfully realized with chiral phosphoric acid (CPA) as catalyst and water as additive. A variety of optically active secondary alcohols were obtained in good to high yields with up to 77% ee. The reaction likely proceeded through a Brønsted acid-promoted double-hydrogen transfer between ketones and ammonia borane via a six-membered concerted transition state.