Synthesis of imidazo[4,5-c]pyrazoles via copper-catalyzed amidine cyclization.

A new synthetic approach to 4-substituted imidazo[4,5-c]pyrazoles is proposed on the basis of the N'-(4-halopyrazol-5-yl)amidine cyclization under the conditions of copper-catalyzed cross-coupling reactions. Using 5-aminopyrazoles and copper catalysts as starting materials, the method is inexpensive and convenient and allows a wide range of substituents at all positions of the imidazo[4,5-c]pyrazole nucleus.