Green procedure for the synthesis of bis(indolyl)methanes in water

A green and environmentally benign protocol for squaric acid catalyst electrophilic substitution reactions of indole derivatives, with various aldehydes in water, in good to excellent yields, is developed. The advantages of low sensitivity towards moisture and oxygen, high tolerance of different functional groups, green reaction media and efficient recyclability make this organocatalyst suitable for both laboratory and industrial scale synthesis of bis(indolyl)methanes under very mild conditions.