Relay iron/chiral Brønsted acid catalysis: enantioselective hydrogenation of benzoxazinones.

An asymmetric hydrogenation reaction of benzoxazinones has been accomplished via a relay iron/chiral Brønsted acid catalysis. This approach provides a variety of chiral dihydrobenzoxazinones in good to high yields (75-96%) and enantioselectivities (up to 98:2 er). It is noteworthy that challenging 3-alkyl-substituted substrates underwent highly enantioselective reduction. A key to success is the utilization of a nonchiral phosphine ligand to reduce disadvantageous background reactions through tuning the catalytic activity of Fe3(CO)12.