Nanosilica Molybdic Acid as a Reusable Catalyst for Chemoselective Synthesis of Novel 4-Dihydropyrano[2,3-c]pyrazoles

Background: A new convenient and practical green synthetic method for nanosilica molybdic acid (nano-SMA) catalyzed chemoselective synthesis of some new 4-dihydropyrano[2,3-c]pyrazoles through a one-pot reaction of 3-methyl-1-phenyl-2-pyrazolin-5-one, ethyl cyanoacetate and aryl aldehydes is described in this study. Results: Nanosilica molybdic acid was synthesized and then characterized by X-ray fluorescence (XRF), powdered X-ray diffraction (XRD), IR spectroscopy and transmission electron microscopy (TEM). Due to the importance of novel catalyst applications, after preparation and characterization of the catalyst, we decided to use nano-SMA for the synthesis of 4-dihydropyrano[2,3-c]pyrazoles. After optimizing conditions, we found that this reaction was performed with 1 mol% of nano-SMA in refluxing EtOH. Then, the generality of the procedure was evaluated by examining various aryl aldehydes under optimized reaction conditions. The data obtained from elemental analysis, 1H and 13C NMR spectra confirmed the proposed products. Conclusion: Overall, we reported a green protocol for the chemoselective synthesis of 4-dihydropyrano [2,3-c]pyrazole derivatives. The advantages of this method are high yield of pure products, reusability of catalyst, short reaction times and a simple workup procedure, that make it an attractive and economical method for the synthesis of these useful heterocycles.