tert-Butyl nitrite-mediated three-component azo coupling of aromatic amines with pyrazolones: synthesis of 4-aryl diazenyl-5-hydroxy pyrazoles.

Herein, we report a simple and efficient method for the room-temperature synthesis of novel 4-aryl diazenyl-5-hydroxy pyrazoles using a three-component reaction involving aromatic amines, tert-butyl nitrite (TBN), and pyrazolones. In this process, TBN serves as the nitrogen source for the in situ generation of the corresponding diazonium salts from aromatic amines. The subsequent coupling proceeds smoothly in the absence of any catalyst or additives. A wide range of anilines and pyrazolone derivatives were found to be compatible with this protocol, demonstrating its broad substrate scope. Considering the presence of azo, hydroxy, and pyrazole moieties, the synthesized compounds are anticipated to exhibit important medicinal properties.