Cinchona-Alkaloid-Derived NN Ligands and Achiral Phosphines for Iridium-Catalyzed Asymmetric Hydrogenation of Heteroaromatic and α-Chloroheteroaryl Ketones

A concise synthesis of cinchona-alkaloid-derived NN ligandsbearingalkyl substituents on chiral nitrogen atoms was described. Iridiumcatalysts containing new chiral NN ligands and achiral phosphineswere effective for the asymmetric hydrogenation of heteroaromaticketones, which afforded corresponding alcohols in up to 99.9% ee.The same protocol was applicable to the asymmetric hydrogenation of alpha-chloroheteroaryl ketones. Most importantly, the gram-scaleasymmetric hydrogenation of 2-acetylthiophene and 2-acetylfuran proceededsmoothly even under 1 MPa of H-2.