Pd/Et3N·HI-Catalyzed Intramolecular C–H Alkylation to Access [a]-Annulated Indoles via Highly Regioselective Ring-Opening of Epoxides

A Pd/Et3N·HI-catalyzed intramolecular C-H alkylation of indoles with epoxides was achieved to furnish N-fused indole frameworks (5-, 6-, and 7-membered rings) bearing an alcohol group. The conversion proceeded smoothly in the presence of a catalytic amount of Et3N·HI together with a palladium catalyst and exhibited great functional group tolerance. The employment of Et3N·HI not only avoids the prior preparation of alkyl halide substrates but also is the key to the high chemoselective ring-opening of epoxides. Preliminary mechanism explorations strongly support a radical pathway, and the catalytic cycle was established tentatively according to the mechanism investigation experiments.