Metal‐free Synthesis of Trisubstituted Pyrazoles by the Reaction Between Hydrazones and Activated Olefins

Abstract The reactivity of various activated olefins towards the [3+2] annulation with hydrazones (aza‐enamines) has been studied. Nitroolefins, methyl vinyl ketone, acrylates and acrylamide were found to react with aldehyde hydrazones of different electronic nature to generate 1,3,5‐/1,3,4–trisubstituted pyrazoles selectively. A detailed optimization study was conducted to derive the best condition for the annulation reaction of different olefin partner and the intermediate dihydropyrazole is also identified.