Reactions of o-(Hydrosilyl)(boryl)benzenes: Intramolecular Activation of Si-H Bond by o-Boryl Group

Hydrosilanes are versatile reagents in organic synthetic chemistry as well as oraganosilicon chemistry. Since the Si-H bond is rather inert, its activation is generally required. Recently electrophilic activation of the Si-H bond by a strong Lewis acid such as triarylboranes has received much attention. The highly electrophilic boron center interacts with the hydrogen on the silicon, which renders the Si-H bond polarized. We report here the intramolecular electrophilic activation of a Si-H bond by an ortho boryl group in o-(hydrosilyl)(dimesitylboryl)benzenes, which leads to (i) dehydrogenative condensation with alcohols and amines and (ii) mesityl-H ligand exchange between the silicon atom and the boron atom to form the o-(silyl)(hydroboryl)benzene intermediates. The o-(silyl)(hydroboryl)benzene intermediates undergo (i) hydroboration to carbonyl compounds and (ii) intramolecular B-H/C-H dehydrogenative cyclization to form the dibenzosilaborins.