A comparison of the asymmetric hydrogenation catalyzed by rhodium complexes containing chiral ligands with a binaphthyl unit and those with a 5,5′,6,6′,7,7′,8,8′-octahydro-binaphthyl unit

The chiral ligands H-8-BINAPO and H-8 BDPAB were synthesized by reacting chlorodiphenylphosphine with H-8-BINOL and H-8-BINAM, respectively. Applications or these ligands in the Rh-catalyzed enantioselective hydrogenation of a variety or (Z)-acetamido-3-arylacrylic acid methyl esters provided chiral amino acid derivatives with good to excellent enantioselectivities (H-8-BINAPO: up to 840% e.e.: H-8-BDPAB: up to 97.1% e.e.). In the hydrogenation of acetamidoacrylic acid, 99%. e.e. was obtained when a [Rh(H-8-BDPAB)] catalyst was used. The catalytic activities and enantioselectivities of [Rh(H-8 BINAPO)](+) and [Rh(H-8-BDPAB)](+) are substantially better than those obtained with the corresponding rhodium catalysts containing BINAPO (up to 64% e.e.) and BDPAB (up to 92.6% e.e.). (C) 2001 Published by Elsevier Science Ltd.