Zwitterionic sulfamic acid functionalized nanoclay: A novel nanocatalyst for the synthesis of dihydropyrano[2,3-c]pyrazoles and spiro[indoline-3,4'-pyrano[2,3-c]pyrazole] derivatives

摘要

Zwitterionic sulfamic acid functionalized nanoclay (MMT-ZSA) was prepared with montmorillonite K10 as template, 3-aminopropyltriethoxysilane as linker and chlorosulfonic acid as a SO3H source. The physical and chemical properties of zwitterionic nanoclay were characterized by the following instrumental techniques: FT-IR spectroscopy, elemental analysis, TGA, DTA, SEM, XRD, elemental analysis and Hammett acidity function techniques. The catalytic activity of MMT-ZSA was investigated in the synthesis of dihydropyrano[2,3 '-c]pyrazoles and spirofindoline-3,4'-pyrano[2,3-c]pyrazole] derivatives via the multicomponent reaction between hydrazine hydrate (or phenyl hydrazine), malononitrile, beta-keto ester and carbonyl compounds (1,2-di ketones and benzaldehyde derivatives) under solvent-free conditions. Using this synthetic method, the title compounds were prepared in high to excellent yields and short reaction times. Other remarkable features include heterogeneous reaction conditions, a much milder procedure, and a wide range of functional group tolerance, high reaction rates, absence of any tedious workup or purification, and reusability of the catalyst. This synthetic protocol also avoids hazardous reagents/solvents and is thus an eco-friendly, alternative approach to the existing methods. (C) 2016 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.