Synthesis and Reactions of Cyclic Silylboranes

Five-membered cyclic silylboranes, 2-(diisopropylamino)-1,1-diorgano-1-sila-2-boracyclopentanes, were synthesized via intramolecular reductive B–Si bond formation with 3-[chloro(diisopropylamino)boryl]-1-(chlorodiorganosilyl)propane. The cyclic silylboranes were thermally stable and could be distilled under a vacuum. The reaction of the cyclic silylboranes with alcohols resulted in a cleavage of the Si–B bond, whereas a reaction with sec-amines led to an amino group exchange on the boron atom. The insertion of alkynes into the Si–B bond of the cyclic silylborane was effectively catalyzed by palladium catalysts, leading to a regioselective formation of seven-membered cyclic alkenes in high yields.