A novel synthesis of pyrazol-3-ones from biacetyl dimer and arenediazonium salts

Abstract

Arenediazonium salts (1) and biacetyl dimer (2), under acidic conditions, yield 1-aryl-5-methylpyrazol-3-ones (3). A simple procedure employing solid diazonium salts is described. Intermediate 2-arylazo-2,5-dimethylfuran-3(2H)-ones (7) are involved in the reaction. In acid media they can be converted into the pyrazolones (3). Their formation is discussed. A possible mechanism for the rearrangement of (7) to (3) is suggested.