Photo-induced ring-maintaining hydrosilylation of unactivated alkenes with hydrosilacyclobutanes.

Increasing attention has been paid to silacyclobutanes because of their wide application in ring opening and ring extension reactions. However, the synthesis of functionalized silacyclobutanes remains an unmet challenge because of the limited functional group tolerance of the reactions with organometallic reagents and chlorosilacyclobutanes. Herein, we report a conceptually different solution to this end through a visible-light-induced metal-free hydrosilylation of unactivated alkenes with hydrosilacyclobutanes. A wide range of unactivated alkenes with diverse functional groups including the base-sensitive acid, alcohol and ketones participated in this reaction smoothly. In particular, the first hydrosilylation reaction of alkenes with dihydrosilacyclobutane provides a facile access to various functionalized alkyl monohydrosilacyclobutanes. Unsymmetrical dialkyl silacyclobutanes have also been synthesized through consecutive hydrosilylation with dihydrosilacyclobutane in one pot. The mechanism study reveals that the Lewis basic solvent could promote the generation of strained silyl radicals by direct light irradiation without a redox-active photocatalyst and the thiol catalyst plays an important role in accelerating the reaction.