Metal-Free Tandem Oxidative Cyclization for the Synthesis of 1,2-Dihydropyridazines and Pyrazoles

Mediated by 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), a novel oxidative coupling of hydrazones and 1,3-diarylpropenes has been disclosed to generate appealing beta,gamma-unsaturated hydrazones, which further undergo 5-exo-trig or 6-endo-trig cascade cyclization to give the respective 1,2-dihydropyridazines or pyrazoles selectively under metal-free conditions. The mechanisms of the coupling and subsequent cyclization are proposed.

Automated summary

A novel oxidative coupling of hydrazones and 1,3-diarylpropenes mediated by DDQ was disclosed, leading to the selective generation of 1,2-dihydropyridazines or pyrazoles through subsequent cyclization under metal-free conditions. The mechanisms of the coupling and cyclization were proposed in the study.