Nucleophilic Substitution at Unactivated Arene C–H: Copper-Catalyzed anti-Selective Silylative Cyclization of Substituted Benzylacetylenes

A new mode of carbon–carbon bond formation via electrophilic activation of a C–H bond has been developed in the context of a copper-catalyzed anti-selective silylative cyclization of benzylacetylenes with silylboronates for the synthesis of 2-silyl-1H-indenes. The reaction proceeds with high regioselectivity for various substituted benzylacetylenes, and the resulting products could be further functionalized. The arene that undergoes cyclization acts as an electrophile with the release of hydride under redox neutral conditions, and the reaction mechanism was probed by the deuterium-labeling experiments and the density functional theory calculations.