A fast and efficient CuI-catalyzed intramolecular C-N coupling reaction of N-(2-bromoaryl)-1H-pyrazol-5-amines to synthesize benzo[4,5]imidazo[1,2-b]pyrazoles has been developed from N-(2-bromoaryl)-thioacetanilides. A series of benzo[4,5]imidazo[1,2-b]pyrazoles were obtained in excellent yields with CuI/heterocyclic ketene aminals catalytic system in the presence of Cs 2 CO 3 in dimethyl sulfoxide (DMSO) at 120 ℃ within 10 min. The reaction provides an fast and efficient protocol to access a series of benzo[4,5]imidazo[1,2-b]pyrazoles in good to high yields.