Phosphine-Free Palladium-Catalyzed C−H Bond Arylation of Free (N−H)-Indoles and Pyrroles

This paper describes a phosphine-free palladium-catalyzed method for direct C-arylation of free (N−H)-indoles and pyrroles with iodo- and bromoarene donors. Employing commercially available materials, this new and operationally simple procedure provides a rapid entry to a wide range of C-arylated (N−H)-indoles including derivatives of tryptamine. In the course of this study, a profound halide effect was uncovered, affecting both the efficiency and regioselectivity of indole arylation.