A General Route to Silacyclohexanones via Regioselective Copper-Catalyzed Borylative Cyclization

A copper-catalyzed regioselective borylative cyclization of chloromethyl butenylsilanes with bis(pinacolato)diboron has been reported. The reaction proceeds via an endo-selective cyclization to deliver 4-silacyclohexyl boronates, which undergo a two-step oxidation sequence to afford 4-silacyclohexanones. DFT calculations corroborate the observed selectivity, highlighting the conformational role of the silicon center in favoring the six-membered rings. This protocol features readily available starting materials, a broad substrate scope, good functional group tolerance, and gram-scale capability. The synthetic utility of the resulting silacyclohexanones is demonstrated through diverse transformations, including ketalization, allylation, Wittig olefination, and Baeyer–Villiger oxidation.