A Phosphotungstate Catalyst with Both Brønsted and Lewis Acid Sites for Synthesis of Bis(indolyl)methane Derivatives

Abstract

The Friedel–Crafts alkylation of indoles with aldehydes is a key method for synthesizing bis(indolyl)methanes (BIMs). With the expanding applications of BIMs in medicine and agriculture, the development of new catalytic strategies to facilitate their synthesis has attracted increasing attention. In this study, we report a mild, cost-effective, and environmentally friendly catalyzed Friedel–Crafts reaction of indoles with aldehydes. The catalyst, phosphotungstate [(CH3)2NH2]9[Sb3(A-α-PW9O34)2]·7H2O (SbPW), was synthesized via a conventional aqueous solution method. The reaction proceeds efficiently at room temperature under solvent-free conditions. Under these conditions, high-yielding reactions were achieved for the synthesis of diarylmethane derivatives from a variety of aliphatic and aromatic aldehydes, thereby expanding the synthetic scope of indole-based compounds. The electrophilic substitution reaction was completed within a short period at room temperature without the need for a solvent, and a possible catalytic mechanism is also proposed.