Hydroalkylation of Vinylarenes by Transition-Metal-Free In Situ Generation of Benzylic Nucleophiles Using Tetramethyldisiloxane and Potassium tert-Butoxide

Abstract

Hydrosilanes and Lewis bases are known to promote various reductive defunctionalizations, rearrangements, and silylation reactions, facilitated by enigmatic silicon/Lewis base-derived reactive intermediates. Despite the wide variety of transformations enabled by this reagent combination, no examples of intermolecular C(sp³)−C(sp³) forming reactions have been reported. In this work, we've identified 1,1,3,3-tetramethyldisiloxane (TMDSO) and KO^tBu as a unique reagent combination capable of generating benzylic nucleophiles in situ from styrene derivatives, which can subsequently react with alkyl halides to give a new C(sp³)−C(sp³) linkage via formal hydroalkylation. Mechanistic experiments suggest that the reaction proceeds through a key hydrogen atom transfer (HAT) step from a hydrosilane reducing agent to styrene, affording a benzylic radical that undergoes reductive radical polar crossover (RRPC) and subsequent S_N2 alkylation.