Transition-Metal-Catalyzed Asymmetric Organic Synthesis via Polymer-Attached Optically Active Phosphine Ligands. 5. Preparation of Amino Acids in High Optical Yield via Catalytic Hydrogenation

Article abstract of DOI:10.1021/jo00327a023

Two new optically active phosphinopyrrolidine monomers were prepared by the reaction of (2S,4S)-4-(diphenylphosphino)-2-<(diphenylphosphino)methyl>pyrrolidine and (2R,4R)-4-(diphenylphosphino)-2-<(diphenylphosphino)methyl>pyrrolidine with acryloyl chloride to give N-acryloyl-(2S,4S)-4-(diphenylphosphino)-2-<(diphenylphosphino)methyl>pyrrolidine (1) and N-acryloyl-(2R,4R)-4-(diphenylphosphino)-2-<(diphenylphosphino)methyl>pyrrolidine (2).Copolymerization of 1 and 2 with hydrophilic comonomers and a divinyl monomer provided cross-linked insoluble polymers containing 3-5percentof 1 or 2 that would swell in polar solvents.Exchange of rhodium (I) onto the polymer gave catalysts which were active for the asymmetric hydrogenation of N-acyl α-amino acids in high optical yields, the phosphine derived from the enantiomer of the naturally occurring 4-hydroxyproline giving (S)-amino acids.The catalysts could be reused with no loss in selectivity by simple filtration.