An ionic liquid mediated Friedel-Crafts addition of arenes to isothiocyanates

Abstract

A new protocol is developed for the synthesis of N-substituted thioamides, employing arenes and isothiocyanates in 1-butyl-3-methylimidazolium chloroaluminate ionic liquid, [bmim]Cl·2AlCl3, as a homogenous Lewis acid catalyst and solvent. The effect of Lewis acidity and the stoichiometry of the ionic liquid on the extent of product formation is studied. Studies reveal that a progressive increase in yields was observed with increasing Lewis acidity, and two equivalents of [bmim]Cl·2AlCl3 was the optimal amount for the reaction. A distinct para selectivity for the incoming thioamido group on activated arenes was observed under ambient conditions.Key words: arenes, isothiocyanates, Friedel–Crafts, ionic liquids, thioamides.