DBU-Based Ionic-Liquid-Catalyzed Carbonylation of o-Phenylenediamines with CO₂ to 2-Benzimidazolones under Solvent-Free Conditions

Herein, a new route was presented to synthesize 2-benzimidazolones via the carbonylation of o -phenylenediamines with CO 2 catalyzed by 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)-based ionic liquids under solvent-free conditions. DBU acetate ([DBUH][OAc]) displayed high efficiency for catalyzing the reactions of CO 2 with o -phenylenediamines, and a series of benzimidazolones were obtained in high yields. It was demonstrated that [DBUH][OAc] could serve as a bifunctional catalyst for these reactions with the cation activating CO 2 and the anion activating o -phenylenediamines. This protocol provides an effective and environmentally friendly alternative route for production of benzimidazolones, and extends the chemical utilization of CO 2 in organic synthesis as well.