Synthesis of Dihydrobenzosiloles and Silacyclopentane via Double Hydroalumination of Terminal Alkynes

We developed an efficient method for the synthesis of dihydrobenzosiloles in 19% to 90% isolated yields from 1-hydrosilyl-2-ethynylbenzenes using two equivalents of diisobutylaluminum hydride. The reaction mechanism involves regioselective double hydroalumination of the alkyne moiety followed by cyclization to 2-alanyldihydrobenzosilole. A silacyclopentane was also synthesized in 97% isolated yield from the corresponding 4-silylbut-1-yne under the same reaction conditions. Although the substrate scope was conducted on a 0.5 mmol scale, a gram-scale reaction of 1-diphenylsilyl-2-ethynylbenzene under the optimized reaction conditions successfully afforded the desired product in 94% isolated yield without loss of reactivity.