Optically Pure 1,2-Bis[(O-alkylphenyl)phenylphosphino]ethanes and Their Use in Rhodium-Catalyzed Asymmetric Hydrogenations of alpha-(Acylamino) acrylic Derivatives

摘要

Optically pure (S,S)-l,2-bis[(o-alkylphenyl)-phenylphosphino]ethanes 1a-d were prepared in four steps from phenyldichlorophosphine via phos-phine-boranes as the intermediates.The rhodium complexes 5a-d of these diphosphines were used for the asymmetric hydrogenations of alpha-(acylamino)-acrylic derivatives including beta-disubstituted derivatives.Markedly high enantioselectivity (78->99%) was observed for the reduction of beta-monosubstituted derivatives.beta-Disubstituted derivatives were also reduced in considerably high enantioselectivity (up to 90%).The single crystal X-ray analysis of the rhodium complex 5c of (5,5)-l,2-bis[phenyl(5',6',7',8'-tetrahy-dronaphthyl)phosphino]ethane (1c) revealed its 6-type structure with face orientation of the two tetra-hydronaphthyl groups and edge orientation of the two phenyl groups.This conformation corresponds to that of the rhodium complex of l,2-bis[(O-methoxy-phenyl)phenylphosphino]ethane (DIPAMP);the rhodium complex of (R,R)-DIPAMP,whose chirality at phosphorus is opposite that of 5c,exhibits a lambda-type structure with the face orientation of the two O-me-thoxyphenyl groups and the edge orientation of the two phenyl groups.The conformational similarity of these rhodium complexes as well as the stereochemi-cal outcome in the asymmetric hydrogenations means that the coordinative interaction of the methoxy group of DIPAMP with rhodium metal is not the main factor that affects asymmetric induction.