Regenerable Dihydrophenanthridine via Borane-Catalyzed Hydrogenation for the Asymmetric Transfer Hydrogenation of Benzoxazinones.

The highly enantioselective transfer hydrogenation of benzoxazinones with chiral phosphoric acids under H 2 was successfully achieved, where boranes promoted the hydrogenation of phenanthridine for the regeneration of dihydrophenanthridine as the hydrogen donor. A variety of dihydrobenzoxazinones were obtained in high yields with up to 99% ee. The current work provides a promising solution to unreactive substrates for frustrated Lewis pair-catalyzed asymmetric hydrogenation.