Oxalic Acid Dihydrate: A Reusable and Cost-Effective Catalyst for the Synthesis of Bis(indolyl)methanes under Solvent-Free Conditions

Oxalic acid as a solid organic acid catalyzed the synthesis of bis(indolyl)methanes by the reaction of indole derivatives and different carbonyl compounds. All the reactions were performed at ambient temperature and completely heterogeneous conditions and the products were obtained in high yields.