Ethylene glycol, an efficient and recoverable medium for copper-catalyzed N-arylation of diazoles under microwave irradiation

Ethylene glycol was used as an efficient and recoverable medium for the reaction of diazoles with aryl iodides and aryl bromides in the presence of CuCl₂ as the catalyst and K₂CO₃ as the base. Consequently, imidazole, benzimidazole, and pyrazole reacted readily under microwave irradiation to give good to excellent yields of their corresponding N-arylated products in relatively short time periods. Apparently, ethylene glycol plays a dual role by activating the catalyst and also providing a homogenous medium for the processes. The reaction medium consisting of the solvent, the base, and the copper salt was recovered and reused successfully in the next several reactions.