Asymmetric Hydrogenation of 3, 4-Methylenedioxy-α-acetamidocinnamic Acid Using Newly Developed Silica Gel-Supported Chiral Rhodium (I) -Phosphine Complexes

Abstract

The asymmetric hydrogenation of 3, 4-methylenedioxy-α-acetamidocinnamic acid was carried out in the presence of a chiral Rh (I) -complex of (2S, 4S) -N-butoxycarbonyl-4-diphenylphosphino-2-diphenylphosphinomethylpyrrolidine (BPPM) adsorbed on hydrophobic silica gel in MeOH- H₂O solvents. Excellent conversions (100%) and a high optical yield (85%) were attained with [Rh (COD) BPPM] ⁺ClO₄^- on methylated silica gel. The adsorption of the complex was improved byintroducing a stearoyl group instead of the butoxycarbonyl group of BPPM. When the recovered catalysts were reused three times, the optical yields decreased gradually from 85 to 69%.