Microwave-assisted synthesis of sydnonyl-substituted imidazoles

3-Aryl-4-formylsydnones 1a–d react with symmetrical 1,2-dicarbonyl compounds, such as benzil (2a), 4,4′-dimethoxybenzil (2b), 4,4′-difluorobenzil (2c), and di-2-thienylethanedione (2d), in glacial acetic acid, using ammonium acetate as the ammonia source, to yield 4,5-diaryl-2-sydnonyl-substituted imidazoles 3a–6d under conventional heating. In a similar treatment, 4,5-diaryl-2-sydnonyl-1-substituted imidazoles 8a–10a can be prepared by the one-pot condensation of 3-(4-ethoxyphenyl)-4-formylsydnone (1d), benzil derivatives, ammonium acetate, and primary amines. However, such reactions, which take 1–3 days at high temperature under classical conditions, are completed successfully within a few minutes under microwave irradiation.