Development of practical rhodium phosphine catalysts for the hydrogenation of β-dehydroamino acid derivatives

The rhodium-catalyzed asymmetric hydrogenation of various, beta-dehydroamino acid derivatives to give optically active,beta-amino acids has been examined. Chiral monodentate 4,5-dihydro-3H-dinaphthophosphepines, which are easily tuned and accessible in a multi-10-g scale, have been used as ligands. The enantioselectivity is largely dependent on the nature of the substituent at the phosphorous atom and on the structure of the substrate. Applying optimized conditions up to 94% ee was achieved.