SiO2/g-C3N4 nanocomposite-catalyzed green synthesis of di-indolyloxindols under mild conditions

In this study, a facile and benign protocol was introduced for the immobilization of SiO2 nanoparticles onto g-C3N4 nanosheets. The corresponding nanocomposite (SiO2/g-C3N4) was characterized by various techniques, including X-ray diffraction, transmission electron microscopy, thermo-gravimetric analysis, and Fourier transform infrared spectra. The activity of a SiO2/g-C3N4 nanocomposite was investigated in C-C bond formation reaction. The Friedel-Crafts 3-indolylation reaction of isatin with indole derivatives was investigated in the presence of a catalytic amount of SiO2/g-C3N4 nanocomposite at ambient temperature in water as a green medium. The results showed that the corresponding products were obtained in good to excellent yields. In addition, the electron-releasing groups in the R-1 position of the indole ring or electron-withdrawing groups on the R-4 position of isatin gave excellent yields (91-95%). Some advantages of this method include short reaction time, excellent yields, easy work-up, and the use of water as a green solvent.