Asymmetric Hydrosilylation of Styrene by Palladium Catalysts Coordinated with Chiral Phosphoramidite Ligands from 3,3'-Disubstituted 1 ,l'-Binaphthols

摘要

Owing to its high catalytic activity, perfect regioselec-tivity, and an easy-manipulation without producing any byproduct, palladium-catalyzed asymmetric hydrosilylation of styrene has become a potent methodology to show their efficiencies of newly-developed chiral monodentate phosphorus ligands recently. Ever since a significant improvement for catalytic activity and enantioselectivity in the hydrosilylation of styrenes was achieved by chiral mono-phosphine (MOP) ligands based on the 2-diphenylphos-phino-1,1'-binaphthyl skeleton, several monodentate phosphorus ligands, such as phosphoramidites, planar chiral monophosphines, and helically chiral phosphines have been applied to the hydrosilylation of styrenes to afford moderate to excellent enantioselectivities. Of those monodentate ligands, H-MOP derivative (R-L1 lacking a sub-stituent at the 2'-position of the binaphthyl and a phosphoramidite ligand (S_A,R_c,R_c)-L2 derived from (S)-1,1'-bi-naphthol and bis((R)-l-phenylethyl)amine have been reported to be the most efficient ligands in the hydrosilylation of styrenes (Figure 1).