A green one-pot three-component synthesis of spirooxindoles under conventional heating conditions or microwave irradiation by using Fe3O4@SiO2-imid-PMAn magnetic porous nanospheres as a recyclable catalyst

An efficient, green and environmentally procedure for the synthesis of spirooxindole derivatives has been developed by a one-pot three-component reaction of isatin derivatives, activated methylene, and 1,3-dicarbonyl compounds in the presence of Fe3O4@SiO2-imid-PMA(n) magnetic nanocatalyst under conventional heating conditions in water or microwave irradiation under solvent-free conditions. The reactions under conventional heating conditions were compared with the microwave-assisted reactions. The suggested method offers several advantages such as excellent yields, short reaction times, operational simplicity, a cleaner reaction, absence of any tedious workup or purification and ease of recovery and reusability of the catalyst by a magnetic field. In addition, the excellent catalytic performance in a water medium and the easy preparation, thermal stability and separation of the catalyst make it a good heterogeneous system and a useful alternative to other heterogeneous catalysts. The catalyst can be easily recovered by a magnetic field and reused for six consecutive reaction cycles without significant loss of activity. Also, the morphology of Fe3O4@SiO2-imid-PMA(n), particle size distribution and leaching of nano H3PMo12O40 (PMA(n)) after reaction cycles were investigated by scanning electron microscopy (SEM), dynamic light scattering (DLS), and inductively coupled plasma (ICP) analyzer.