Transition-Metal-Catalyzed Asymmetric Organic Synthesis via Polymer-Attached Optically Active Phosphine Ligands. 6. Asymmetric Hydrogenation with Polymer Catalysts Containing Optically Active Pendent Alcohols

Article abstract of DOI:10.1021/jo00327a024

Three acrylate comonomers, (S,S), (R,R) and racemic 1-methyl-2-hydroxypropyl acrylate (7a-c), were prepared from the corresponding isomers of 2,3-butanediol.The acrylates were copolymerized with ethylene dimethacrylate and N-acryloyl-(2S,4S)-4-(diphenylphosphino)-2-<(diphenylphosphino)methyl>pyrrolidine (8) to give cross-linked resins containing phosphinopyrrolidines and optically active alcohols.Polymers containing the 4,5-bis<(diphenylphosphino)methyl>-1,3-dioxolane unit (DIOP) were prepared by copolymerizing acrylates 7a-c with ethylene dimethacrylate and 2-p-styryl-4,5-bis<(tosyloxy)methyl>-1,3-dioxolane (1) and treating the polymers with an excess of sodium diphenylphosphide.Exchange of Rh(I) onto these polymers provided catalysts that hydrogenated 2-acetamidoacrylic acid in tetrahydrofuran.The enantiomeric excesses obtained with the polymer-bound catalysts varied with the structure of the pendent alcohol, suggesting the participation of the polymer-bound alcohol at the catalyst site to provide an alcohol-like environment.A difference in enantiomeric excess (ee) was noted when catalysts containing either R or S alcohols were used.