Access to Chiral Silanes via Asymmetric Hydrosilylation

Significance

Asymmetric hydrosilylation of both β-aryl and β-alkyl-β-silyl enoates 1 was effected by CuH complexed to the chiral ligand PPF-P(t-Bu)₂ in high ee values. Hindered substrates reacted with catalyst loadings of 1 mol%, the reaction conditions are quite mild (<0 °C) and neutral. The E- vs Z-geometry of the enoate did not affect the rate of hydrosilylation, but showed that the reduction was stereospecific. Facial selectivity of the CuH-(R,S)-PPF-P(t-Bu)₂ complex afforded chiral esters with >90% ee in most cases. A catalyst loading of 0.1 mol% is also possible, although the reduction required a longer time (36 vs 9 h) and a higher concentration (0.7 vs 0.5 M). A chemically diverse array of Z- and E-β-silyl enoates bearing either β-aryl or β-alkyl substituents were reduced in high chemical yields.