Abstract: Silicon hydrides, alkynylsilanes, and alkoxylsilanes were activated by fluoride in the presence of bisguanidinium catalyst to form hypervalent silicate ion pairs. These activated silicates undergo 1,4-additions with chromones, coumarins, and α-cyanocinnamic esters generating enolsilicate intermediates, for a consequent stereoselective alkylation reaction. The reduction-alkylation reaction proceeded under mild conditions using polymethylhydrosiloxane, a cheap and environmentally friendly hydride source. The addition-alkylation reactions with alkynylsilanes and alkoxylsilanes resulted in the construction of two vicinal chiral carbon centers with excellent enantioselectivities and diastereoselectivities (up to 99% ee, >99:1 dr). Density functional theory calculations and experimental NMR studies revealed that penta-coordinated silicates are crucial intermediates.
Full Text available at: https://pubs.acs.org/doi/10.1021/jacs.0c00183