P-Chiral Bidentate Phosphine Ligands for Catalytic Asymmetric Reactions

摘要

Optically active phosphine ligands are known to play an impotant role in transition-metal-catalyzed asymmetric reactions. While an enormous number of chiral ligands have been reported so far, together with the spectacular development of highly efficient asymmetric catalyses, the design and synthesis of a new class of ligands remain an important research subject in this field. Previously, we reported P-chiral bidentate phosphine ligands in which a bulky alkyl group (t-Bu group) and a methyl group (the smallest alkyl group) are each bonded to a phosphorus atom (BisP~* and t-Bu-QuinoxP~*). These ligands exhibit very high enantioselectivities in representative asymmetric catalyses by virtue of the asymmetric environment constructed by bulky and small alkyl groups. The results led us to adopt more bulky group or smaller group into those ligands to construct more effective asymmetric environment. Herein, we report the synthesis and enantioselectivities of new P-chiral ligands that possesses 1-adamantylmethylphosphino group or alkynyl(t-butyl)phosphino group.