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.
Twenty-five diverse pyrazolo[3,4-d]-4,5-dihydropyrimidines were synthesized in 73-91% yield through TMS-promoted [5+1] heterocyclization of aldehydes with pyrazolylamidines.