An unusual trans-hydrosilylation of prochiral 1,1-disubstituted cyclopropenes revealing the different nature of asymmetric palladium and rhodium catalysis

Abstract

Catalytic asymmetric hydrosilylation is an extremely important and atom-economical chemical transformation in the field of catalysis and synthetic chemistry. Although stereospecific hydrosilylation provides a general strategy for elaborating diastereo- and enantioselective synthesis of optically pure organosilicon compounds, existing methods for accessing Si–C bond-forming hydrosilylation of alkenes rely almost entirely on terminal olefins. Herein, we reported a highly enantioselective palladium-catalyzed hydrosilylation reaction of 1,1-disubstituted carbonyl cyclopropenes with dihydrophenylsilane. We demonstrated that the palladium catalyst system provided stereodivergence to enable the trans-type diastereoselective synthesis of a wide variety of silylcyclopropanes bearing a quaternary carbon-stereocenter with good diastereo- and enantioselectivities (up to >19 : 1 dr and 97% ee). The preliminary experimental results of mechanistic studies showed that the steric repulsion between the TADDOL-derived phosphoramidite ligand and substrate would be an important factor, allowing access to different and reversed diastereospecific hydrosilylation in comparison to rhodium catalysis.