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

摘要

Hydrazonoyl 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.