Nano TiO2/SiO2: An efficient and reusable catalyst for the synthesis of oxindole derivatives

Nano TiO2 supported on SiO2 (Nano TiO2/SiO2) as a solid Lewis acid, was found to be an effective and reusable catalyst for the condensation reaction of indoles with isatins to afford the corresponding bis(indolyl)oxindoles at 50 °C under solvent-free conditions. The efficacy of the catalyst was also examined in the reaction of pyrrole and 3-methylindole with isatin. The catalyst has been recovered and its reusability confirmed in 5 runs. A plausible mechanism of condensation has also been suggested.