Intramolecular Silylarylation of α-Olefins Enabled by Disulfide Co-Catalysis and Maintained by Proton-into-Silylium...

A "bioinspired" silylarylation of unactivated terminal alkenes involving formal thiosilylation of the C═C double bond followed by an intramolecular electrophilic aromatic substitution (S_EAr) is disclosed. The reaction is initiated by weak coordination of a silylium ion to the terminal alkene to form a β-silicon-stabilized carbenium ion that is subsequently captured by an external sulfide co-catalyst to yield a sulfonium-ion electrophile. Nucleophilic attack of the tethered arene then affords a highly Brønsted acidic arenium ion, which allows for protodearylation of an arylsilane additive for the regeneration of the silylium ion stabilized by the sulfur donor. This step is also modulated by the sulfide donor as a proton shuttle thereby mitigating side reactions such as competing hydroarylation or alkene oligomerization. This ionic alkene silylarylation is a silylium-ion-mediated reaction where a sulfide co-catalyst balances the reactivities of the involved cationic intermediates, eventually improving the overall efficiency of the process.