Organocatalytic Friedel–Crafts arylation of aldehydes with indoles utilizing N-heterocyclic iod(az)olium salts as halogen-bonding catalysts

Abstract

The Friedel–Crafts arylation is among the most known organic reactions, usually being promoted by a Lewis acid, that have been employed for the synthesis of bis-indolyl methanes. Herein, we report a mild, inexpensive, green and organocatalytic protocol for the promotion of a Friedel–Crafts-type reaction between indoles and aldehydes, where N-heterocyclic iod(az)olium salts are utilized as halogen-bonding catalysts, leading to the double addition of the indole motif. A variety of aliphatic and aromatic aldehydes were converted into diarylmethanes in good to high yields, while the scope of indoles was also investigated. Water was employed as the solvent, while the reaction time was short. The reaction mechanism was also studied.