The Remarkable Cooperative Effect of a Brønsted‐Acidic Ionic Liquid in the Cyclization of 2‐Aminobenzamides with Ketones

Abstract

An unprecedented role of an imidazolium Brønsted acidic ionic liquid was found in the formation of 2,2‐disubstituted quinazolin‐4(1 H )‐one derivatives; both the C2‐H of the imidazolium moiety and an acidic proton were necessary and simultaneously took part in the catalysis. A library of quinazolin‐4(1 H )‐ones was prepared from readily available ketones and 2‐aminobenzamides; excellent yields were obtained through simple crystallization under solvent‐free conditions with lower E factors. The catalyst could be reused over five consecutive runs without any significant loss in catalytic activity. This method produces only water as a byproduct and represents a green synthetic protocol. A clean reaction, no chromatographic purification, easily accessible reactants, a metal‐free and solvent‐free process, and environmentally friendly reaction conditions are the notable advantages of this procedure. The possible role of the C2‐H of the imidazolium moiety in catalysis was studied by mass spectrometry.