A green synthesis of spirooxindole derivatives catalyzed by SiO2@g-C3N4 nanocomposite

Abstract

In this study, SiO2 nanoparticles were immobilized onto the surface of g-C3N4 nanosheets. The characterization of SiO2@g-C3N4 nanocomposite has been done by Fourier transform infrared spectra, X-ray diffraction, thermo-gravimetric analysis, scanning electron microscopy and transmission electron microscopy. The one-pot synthesis of spirooxindole derivatives was investigated via C–C bond formation reaction in the presence of a catalytic amount of SiO2@g-C3N4 nanocomposite using isatin (1 mmol), dimedone (1 mmol) and malononitrile (1 mmol) at ambient temperature in EtOH/water (1:1) media and the corresponding products were synthesized in excellent yields (90–95%) in short time (3–5 min). 4-Hydroxycoumarin was also subjected to the reaction instead of 1,3-diketones under similar conditions and the reactions proceeded in a longer time than for 1,3-diketones (8–11 min) with the products being obtained in 87–95% yields. The advantages of this catalyst include mild reaction conditions, a green and inexpensive nanocatalyst and green media. The nanocomposite was reused several times and applied in the next run without loss of reactivity.