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‐CO 2 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.