PEG1000-Based Dicationic Acidic Ionic Liquid/Solvent-Free Conditions: An Efficient Catalytic System for the Synthesis of Bis(Indolyl)methanes

Abstract

An efficient procedure has been researched for the solvent-free synthesis of bis(indolyl)methanes via a one-pot reaction of indoles and aldehydes or ketones promoted by PEG 1000 -based dicationic acidic ionic liquid (PEG 1000 -DAIL). The catalyst PEG 1000 -DAIL could be reused seven times with excellent results. Furthermore, through this method, a highly chemoselective reaction of benzaldehyde and acetophenone with indole could be achieved.

A simple and efficient preparation of bis(indolyl)methanes catalyzed by HCl/silica gel under solvent-free conditions

“…Among numerous methods, the Friedel-Crafts acylation reaction or electrophilic substitution reaction of indoles with aldehydes or ketones under a variety of reaction conditions is a classical strategy. Numerous reagents and reaction conditions were developed and reported to access BIMs including Brønsted or Lewis acid, [22][23][24][25][26][27][28][29][30] iodine, 31 methanol, 32 cyclodextrin/electrolysis, 33 metal salts, 22,[34][35][36][37] ionic liquids, 22,[38][39][40] visible light, [41][42] surfactants, 43 vitamin B1 44 and enzymes. 45 Moreover, the preparation of BIMs by using solid acidic catalysts including amberlyst, zeolite, sulfated zirconia, silica sulfuric acid, montmorillonite clay K-10, AlPW12O40, H3PW12O40, TiO2, ZrOCl2/SiO2, HClO4-SiO2, P2O5/SiO2 and Lewis acid-surfactant-SiO2 has also been investigated.…”