Ultrasound mediated green synthesis of pyrano[2,3-c]pyrazoles by using Mn doped ZrO2

Abstract

Mn doped zirconia is utilized as an environmental-friendly and efficient catalyst for an ultrasound mediated four-component coupling reaction, containing dimethylacetylenedicarboxylate/ethyl acetoacetate, hydrazine hydrate, malononitrile, and aromatic aldehyde. These reactions were performed under green solvent conditions, to yield pyrano[2,3-c]pyrazole-3-carboxylate/pyrano[2,3-c]pyrazole-5-carbonitrile derivatives (5a–g and 7a–g) with good to excellent yields (88–98%). The structures of the compounds were identified and confirmed by 1H NMR, 15N NMR, 13C NMR, FT-IR and HR-MS spectral data. The prepared catalyst Mn/ZrO2 was synthesized and fully characterized by various techniques including P-XRD, BET, SEM and TEM analysis. The main benefits of this process are short reaction times, easy work-up, reusability of the catalyst and no chromatographic purifications. Keywords: Ultrasound, Green synthesis, Multicomponent reaction, Pyrazoles, Heterogeneous catalyst, Reusability