Copper- and Palladium-Catalyzed Intramolecular Aryl Guanidinylation:  An Efficient Method for the Synthesis of 2-Aminobenzimidazoles

[reaction: see text] The formation of 2-aminobenzimidazoles via intramolecular C[bond]N formation between an aryl halide and a guanidine moiety can be achieved using either copper or palladium catalysis. Inexpensive copper salts such as CuI are generally superior to the use of palladium catalysts. Regioselective cyclizations, where R(3) = H, can be achieved in high yield under CuI/1,10-phenanthroline-catalyzed conditions, whereas palladium catalysis results in the formation of regioisomeric products.