Remarkably Low Catalyst Loading in Brønsted Acid Catalyzed Transfer Hydrogenations: Enantioselective Reduction of Benzoxazines, Benzothiazines, and Benzoxazinones

A highly efficient transfer hydrogenation of benzoxazines, benzothiazines, and benzoxazinones with as low as 0.01 mol % binol phosphate catalyst furnishes the dihydro-2H-benzoxazines, -benzothiazines, and -benzoxazinones in good yields and with excellent enantioselectivities (see scheme). Particularly noteworthy are the mild reaction conditions and the wide scope of substrates, including sulfur-containing compounds.