Theophylline Hydrogen Sulfate: A green and efficient catalyst for synthesis of 3,3-bis(1H-indol-3-yl)indolin-2-one derivatives

A new green protocol for the synthesis of 3,3-bis(1H-indol-3-yl)indolin-2-one derivatives by reacting isatin with indole in the presence of Theophylline Hydrogen Sulfate as a new solid acid, a highly effective and reusable catalyst. This reaction was carried out by using aqueous ethanol as a solvent system at room temperature with constant stirring. A highly effective solid acid catalyst, short reaction time, better to excellent yields of the products, safe and environmentally benign reaction conditions are some of the benefits of the present synthetic method.