Silicotungstic acid (H4SiW12O40): An efficient Keggin heteropoly acid catalyst for the synthesis of oxindole derivatives

Condensation of various isatins with heteroaromatics (indoles and pyrrole) has been carried out in the presence of catalytic amount of silicotungstic acid (STA) at room temperature to form their corresponding 3,3-bis(indolyl)- and 3,3-bis(2-pyrrolyl)oxindoles. The mechanistic aspects of the reaction have also been discussed.