Highly Enantioselective Hydrogenation of α-Dehydroamino Acids by Rhodium Complexes with New Unsymmetric P−Chirogenic Bisphosphine Ligands
摘要:
[GRAPHICS]New rhodium catalysts with unsymmetric P-chirogenic bis(phosphino)ethanes, BisP*-Rh, exhibited very high enantioselectivity (98-99%) in the hydrogenation of alpha -dehydroamino acid derivatives. Such high enantioselectivity should result from the asymmetric environment around the Rh atom, as was shown in the molecular structure of the catalyst analyzed by X-rays, The asymmetry can be controlled by the combination of the alkyl groups on the two phosphorus atoms.
Air-stable P-Chiral Bidentate Phosphine Ligand with (1-Adamantyl)methylphosphino Group
作者:Tsuneo Imamoto、Atsushi Kumada、Kazuhiro Yoshida
DOI:10.1246/cl.2007.500
日期:2007.4.5
Air-stable diphosphine ligand, (R,R)-2,3-bis((1 -adamantyl)-methylphosphino)quinoxaline, was prepared by the reaction of enantiomerically pure (S )-(l-adamantyl)methylphosphine-borane with 2,3-dichloroquinoxaline. The ligand exhibited excellent enantioselectivities in Rh-catalyzed asymmetric hydrogenation and Pd-catalyzed asymmetric ring-opening reaction.
P-Chirogenic phosphine/sulfide hybrid ligands 1 were prepared by the use of optically active phosphine-boranes as the intermediates. The palladium complexes of the ligands exhibited high catalytic activity and enantioselectivity in allylic alkylation of 1-acetoxy-1,3-diphenylprop-2-ene with malonate esters.
ω-Haloalkylphosphine derivatives undergo the intramolecular nucleophilicsubstitution reaction upon treatment with a strong base, yielding either cycloalkylphosphine derivatives or heterocyclic phosphine derivatives. The selectivity of the cyclization of (ω-haloalkyl)alkylarylphosphine derivatives depends strongly on the distance between the electrophilic and nucleophilic carbon atoms and the structure of the phosphorus