Synthesis of Bis(indolyl)methanes Using Recyclable PEG-Supported Sulfonic Acid as Catalyst

An operationally simple, efficient and environmentally benign synthetic method to bis(indolyl)methanes has been developed in good yields (80-96%) by electrophilic substitution reactions of indole with aldehydes or ketones in methanol in the presence of 5 mol% of poly (ethylene-glycol) (PEG) supported sulfonic acid with respect to indole under mild conditions. Recovery and recycling of the poly (ethylene-glycol)-supported catalyst were also described. Graphical Abstract A simple, facile and environmentally benign synthesis of bis(indolyl)methanes in good yields by reaction of indole with aldehydes or ketones in methanol using recyclable PEG-supported sulfonic acid as catalyst is described.