An Efficient Synthesis of 1,3‐Disubstituted Pyrazoles from 2‐Acylaziridines

We developed an efficient and environmentally benign method for pyrazole synthesis by condensation between 2‐acylaziridines and hydrazine‐CO2 salts in high yields. The sequential reactions involved include an acid‐catalyzed intramolecular aziridine ring opening and a subsequent benzylamine elimination. In additional to the ease of handling the hydrazine as a solid without any smell, all of the processes were carried out with no organic solvent, except for a small amount of phenol as an acid catalyst. What goes around, comes around: An efficient and environmentally benign method for pyrazole synthesis by condensation between 2‐acylaziridines and solid hydrazines was developed. The reaction proceeded in high yields by intramolecular aziridine ring opening and elimination of benzylamine as key reactions. All of these odorless processes were carried out with no organic solvent and the hydrazine as solid.