Facile and efficient method for the synthesis of tetrahydrobenzo [b] pyrans and spirooxindoles catalysed by nano-Fe3O4@dextrin/Si(CH2)3/DABCO as a natural-based nanocatalyst in green media

As a natural-based catalyst, nano-Fe3O4@dextrin/Si(CH2)3/DABCO was fabricated and characterized with different analytical methods such as field emission scanning electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, X-ray mapping, energy-dispersive X-ray spectroscopy, thermogravimetric analysis, and vibrating sample magnetometer. The mentioned new natural magnetic nanocatalyst was employed for the three-component synthesis of tetrahydrobenzo[b]pyrans and spirooxindoles from aromatic aldehyde or isatin, malononitrile, and 1,3-dicarbonyl compounds in green media for the required time. The major advantages of these protocols include atom economy, short time of reaction, simplicity of operation, lack of toxic solvents, excellent yields of products, easiness of separation, and reusability of the catalyst.