Abstract
Chiral rhodium (I) complexes of (-)-2, 3-O-isopropylidene-2, 3-dihydroxy-1, 4-bis (diphenylphosphino) butane (DIOP) and (2S, 4S) -N-butoxycarbonyl-4-diphenylphosphino-2-diphenyl-phosphinomethylpyrrolidine (BPPM) were fixed on charcoal which had been pretreated with metal acetates and triethylamine, and the hydrogenation of α-acetamidocinnamic acid was performed in an ethanol-H2O (1 : 1) mixture. L-N-Acetyl- (R) -phenylalanine was obtained in optical yields of 70.5% with RhCl (COD) -DIOP-charcoal catalyst and 86.5% with RhCl (COD) -BPPM-charcoal catalyst. The optical yields were affected by hydrogen pressure, reaction temperature, the concentration of the substrate, and the composition of the solvent. The recovered catalyst retained its activity well and could be re-used repeatedly for enantioface-differentiating hydrogenation, provided that it was kept under a nitrogen atmosphere throughout.
