Rhodium(I) catalyzed asymmetric hydrogenation of enamines

The asymmetric hydrogenation of prochiral electron-rich enamines with rhodium(I) diphosphine and diphosphinite catalysts is described. The reaction is strongly sensitive to the ligand applied. Good results are observed with catalysts based on (R,R)-DIOP, K-beta(+)-OH, (R,R)-bdpch and other ligands forming seven-membered chelates with the metal. It is shown, that by conversion of a cyclic imine, which could not be hydrogenated, into the corresponding enamine a substrate is formed which is smoothly reduced at 1 bar initial hydrogen pressure by up to 72% ee. (C) 2000 Elsevier Science Ltd. All rights reserved.