Pd/Et 3 N·HI-Catalyzed Intramolecular C-H Alkylation to Access [ a ]-Annulated Indoles via Highly Regioselective Ring-Opening of Epoxides.

A Pd/Et 3 N·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 Et 3 N·HI together with a palladium catalyst and exhibited great functional group tolerance. The employment of Et 3 N·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.