Palladium-Catalyzed Synthesis of Polysubstituted Pyrazoles by Ring-Opening Reactions of 2H-Azirines with Hydrazones

A palladium–catalyzed ring-opening reaction of 2H-azirines with hydrazones has been developed. This protocol provides an alternative route for the construction of various polysubstituted pyrazoles with a wide substrate scope. Moreover, a plausible mechanism is proposed for this reaction, which should further enrich the chemical conversion of 2H-azirines.