Copper- and palladium-catalyzed intramolecular aryl guanidinylation: An efficient method for the synthesis of 2-aminobenzimidazoles

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