Copper-Catalyzed Double C(sp3)-Si Coupling of Geminal Dibromides: Ionic-to-Radical Switch in the Reaction Mechanism.

A method for converting geminal dibromides into 1,1-disilylated alkanes is reported. The reaction is promoted by a copper(I) catalyst generated in situ from CuBr·SMe2 as a precatalyst and 4,4'-di- tert-butyl-2,2'-bipyridine (dtbpy) as a ligand. A Si-B reagent is used as the silicon pronucleophile. It is shown that the two C(sp3)-Si bond-forming events differ in mechanism, with the first being ionic and the second being radical.