Acid-Catalyzed 1,3-Dipolar Cycloaddition of 2H‑Azirines with Nitrones: An Unexpected Access to 1,2,4,5-Tetrasubstituted Imidazoles

The first 1,3-dipolar cycloaddition of 2H-azirines with nitrones, a straightforward approach toward the regioselective synthesis of 1,2,4,5-tetrasubstituted imidazoles, is reported. This trifluoroacetic acid-catalyzed protocol tolerates a broad range of aliphatic and aromatic substrates, offering an efficient access to highly diverse, multisubstituted imidazoles in isolated yields up to 83% under mild conditions.