Economic preparation of 1,3-diphenyl-1,3-bis(diphenylphosphino)propane:: a versatile chiral diphosphine ligand for enantioselective hydrogenations

The enantioselective hydrogenation of 1,3-diarylpropane-1,3-diones with chiral Ru(II)-diphosphine catalyst has been studied. In a first approach it was found, that Tol-BINAP together with Ru(COD)methallyl(2) formed the most selective catalyst. One of the C-2-symmetric enantiopure 1,3-diols obtained in turn was transformed via its 1,3-di-O-mesylate into 1,3-bisdiarylphosphines. One of them, 1,3-diphenyl-1,3-bis(diphenylphosphino)propane, could be advantageously utilized as a ligand for the efficient enantioselective Ru-catalyzed hydrogenation of its own 1,3-diketone precursor. Thus, the condition for a 'cross self-breeding' catalytic system is fulfilled. A further reduction of the preparation costs could be achived by application of RuCl3.H2O instead of other more expensive precatalyst precursors without compromosing the enantioselectivity. The ligand was used in the Rh(I)-catalyzed asymmetric hydrogenation of model substrates and beta-amino acid precursors where up to 97% ee could be achieved. (C) 2003 Elsevier Ltd. All rights reserved.