Boron-catalyzed silylative reduction of quinolines: selective sp3 C-Si bond formation.

A silylative reduction of quinolines to synthetically versatile tetrahydroquinoline molecules involving the formation of a C(sp(3))-Si bond exclusively β to nitrogen is described. Triarylborane is a highly efficient catalyst (up to 1000 turnovers), and silanes serve as both a silyl source and a reducing reagent. The present procedure is convenient to perform even on a large scale with excellent stereoselectivity. Mechanistic studies revealed that the formation of a 1,4-addition adduct is rate-limiting while the subsequent C(sp(3))-Si bond-forming step from the 1,4-adduct is facile.