Synthesis of spiro[pyrazoloquinoline-oxindoles] and spiro[chromenopyrazolo-oxindoles] promoted by guanidine-functionalized magnetic Fe3O4 nanoparticles

Magnetic nanoparticles (MNPs) Fe₃O₄-immobilized guanidine (Fe₃O₄ MNPs-guanidine) have been used as an efficient catalyst for the preparation of spiro[pyrazoloquinoline-oxindoles] and spiro[chromenopyrazolo-oxindoles] by four-component reactions of phenylhydrazine or hydrazine hydrate, isatins, ketoesters and naphthylamine or 2-naphthol under reflux condition in ethanol. This method provides several advantages including mild reaction conditions, the applicability to a wide range of substrates, the reusability of the catalyst and low catalyst loading.