Reverse Regioselectivity in the Ultrasound‐Promoted Synthesis of 1,3,4‐Tri‐Substituted Pyrazoles via [3+2] Cycloaddition of Hydrazonoyl Chlorides with β‐Nitrostyrenes

Abstract

AbstractHydrazonoyl chlorides react with β‐nitrostyrenes in ethanol under the clean action of ultrasonic irradiation. The reaction proceeds at room temperature via 1,3‐dipolar cycloadditions of in situ generated nitrile imine with β‐nitrostyrenes with concurrent elimination of HCl and HNO2 to afford 1,3,4‐trisubstituted pyrazoles with good to high yields and excellent regioselectivity in a short time.