Intermolecular Carbosilylation of α-Olefins with C(sp 3 )-C(sp) Bond Formation Involving Silylium-Ion Regeneration.

A regioselective addition of alkynylsilanes across unactivated, terminal alkenes is reported. The reaction is initiated by the capture of a sterically unhindered silylium ion by a silylated phenylacetylene derivative to form a bis(silylated) ketene-like carbocation. This in situ-generated key intermediate is the actual catalyst that maintains the catalytic cycle by a series of electrophilic addition reactions of silylium ions and β-silicon-stabilized carbocations. The computed reaction mechanism is fully consistent with the experimental findings. This unprecedented two-component carbosilylation establishes a C(sp 3 )-C(sp) bond and a C(sp 3 )-Si bond in atom-economic fashion.