Microwave-Assisted Synthesis of Ethyl 1,3-Disubstituted-1,6-dihydropyrrolo[2,3-c]pyrazole-5-carboxylates.

A novel series of ethyl 1,3-disubstituted-1,6-dihydropyrrolo[2,3-c]pyrazole-5-carboxylates can be rapidly and efficiently synthesized in excellent yields by condensing a variety of 1,3-substituted-4-formyl-5-chloropyrazole with ethyl isocyanoacetate in the presence of 1-methyl-3-butylimidazolium hydroxide under microwave irradiation. The simple experimental procedure, DMSO-free condition, short period of conversion, and excellent yields are the advantages of the present method. The structures of the novel compounds are confirmed by IR, 1H NMR, 13C NMR, MALDI-TOF MS, and elemental analysis. [ABSTRACT FROM AUTHOR]