Abstract
Modified DIOPs, (4R, 5R)-4-(diaryl- or dialkylphosphino)methyl-5-(diarylphosphino)methyl-2, 2-dimethyl-1, 3-dioxolanes, were prepared on the basis of our design concept, and used as ligands for the rhodium(I)-catalyzed asymmetric hydrogenations of ketopantolactone, itaconic acid, demethyl itaconate, and β-aryl-substituted itaconic acid derivatives. A neutral rhodium(I)-complex of (4R-trans)-dicyclohexyl[[5-[(diphenylphosphino)methyl]-2, 2-dimethyl-1, 3-dioxolan-4-yl]methyl]phosphine (DIOCP) bearing both a dicyclohexylphosphino group and a diphenylphosphino group was found to be a more efficient catalyst than the original DIOP in the asymmetric hydrogenation of ketopantolactone. Modified DIOPs bearing electron-donating groups at their para positions were efficient ligands for the rhodium(I)-catalyzed asymmetric hydrogenations of itaconic acid and its derivatives; in particular, (4R-trans)-[(2, 2-dimethyl-1, 3-dioxolane-4, 5-diyl)bis(metylene)]bis[bis(4'-methoxy-3', 5'-dimethylphenyl)phosphine] (MOD-DIOP) bearing both a p-methoxy group and two m, m'-methyl groups on each phenyl group showed much higher enantioselectivity and catalytic activity than DIOP.
