Electrochemical-enabled synthesis of azopyrazoles via pyrazolone fragmentation

Azopyrazoles are high-value compounds with applications in the pharmaceutical, agrochemical, and food industries.¹ Despite their properties, the synthesis of azopyrazoles relies on the preparation of unstable diazonium salts,² transition metal salts,³ or Brønsted acidic ionic liquids.⁴ To develop a safer and greener synthetic method, we propose organic electrosynthesis as an alternative approach for the preparation of azopyrazoles. Under electrolysis in the presence of oxygen, the pyrazolone is proposed to undergo oxidative fragmentation. We hypothesize that this process generates a diazonium salt in situ, which subsequently reacts at the α-carbonyl position of pyrazolone molecule through azo coupling, ultimately affording the azopyrazole. Preliminary optimization using 2,5-diphenyl-2,4-dihydro-3H-pyrazol-3-one as the substrate in methanol, lithium perchlorate as the supporting electrolyte, and an excess of TFA at 10 mA current yields the desired product in 28% isolated yield. Next steps will focus on improving the reaction yield, evaluating the substrate scope, and elucidating the reaction mechanism