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

Abstract

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 of these ligands in the Rh-catalyzed enantioselective hydrogenation of a variety of ( Z)-acetamido-3-arylacrylic acid methyl esters provided chiral amino acid derivatives with good to excellent enantioselectivities (H 8–BINAPO: up to 84.0% 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.).