Synthesis and application of peripherally alkyl-functionalized dendritic pyrphos ligands: Homogeneous-supported catalysts for enantioselective hydrogenation

A new series of dendritic ligands with a chiral diphosphine located at the focal point have been synthesized through coupling of (R, R)-3,4-bis(biphenylphosphino)pyrrolidine (pyrphos) with peripherally alkyl-functionalized benzoic acid dendrons. These ligands were employed in the Rh-catalyzed asymmetric hydrogenation of prochiral dehydroamino acids, exhibiting excellent catalytic activities and enantioselectivities. The second-generation dendritic catalyst could be recovered by simple liquid-liquid biphasic separation and reused four times without serious loss of its activity and selectivity. (C) 2009 Elsevier B.V. All rights reserved.