Cross-linked sulfonated polyacrylamide (Cross-PAA-SO3H) attached to nano-Fe3O4 as a superior catalyst for the synthesis of oxindoles

Abstract

Crosslinked sulfonated polyacrylamide (Cross- PAA- SO3H) attached to nano - Fe3O4 as an efficient heterogeneous solid acid catalyst has been used for the preparation of spiro[ pyrazoloquinoline - oxindoles] and spiro[ chromenopyrazolo - oxindoles] through a four-component reactions of phenylhydrazine or hydrazine hydrate, isatins, ketoesters and naphthylamine or 2 - naphthol under reflux condition in ethanol.Spirooxindoles have appeared as a series of significant heterocycles due to their presence in a wide spectrum of natural and synthetic organic compounds. These activities make spirooxindoles attractive goals in organic synthesis. The modifying crosslinked polyacrylamides make them attractive objects in chemistry and polymer science. Sulfonated polyacrylamides have unique characteristics such as high strength, hydrophilicity, and proton conductivity. The statistic of results from SEM images clearly demonstrate that the average size of Cross-PAA-SO3H@nano-Fe3O4 is about 7-25 nanometers. The remarkable advantages of this methodology are easy work-up, short reaction times, high to excellent product yields, operational simplicity, low catalyst loading and reusability of the catalyst.