Ligandless Palladium-Catalyzed Regioselective Direct C–H Arylation of Imidazo[1,2‑a]imidazole Derivatives

Herein a novel access to functionalizable 6-substituted imidazo­[1,2-a]­imidazole scaffolds is described. The reactivity of this heterobicyclic unit toward direct C–H arylation was studied, and conditions allowing regioselective arylation at position 3 were successfully developed. The practicability of this method is manifested by the ligandless conditions and low catalyst loading. The strategy is functional group tolerant and provides rapid access to a large variety of 3,6-di­(hetero)­arylated imidazo­[1,2-a]­imidazole derivatives. A second arylation at position 2 was then carried out, and a library of diversified 2,3,6-tri­(hetero)­arylated imidazo­[1,2-a]­imidazoles was generated in good yields. A one-pot, two-step procedure was finally developed.