Synthesis and Antioxidant Activity of Some New Thiazolyl–Pyrazolone Derivatives

3‐Methyl‐1‐thiocarbamoyl‐2‐pyrazolin‐5‐one has been utilized as a core for the synthesis of some 1‐(thiazol‐2‐yl)‐pyrazolin‐5‐one derivatives through diazo‐coupling reaction and/or Knoevenagel condensation followed by heterocyclization with some α‐halogenated reagents such as bromoacetone, phenacyl bromide, and ethyl bromoacetate. Base prompted addition of the core compound to an equimolar amount of phenyl isothiocyanate furnished 3‐methyl‐4‐phenylthiocarbamoyl‐1‐thiocarbamoyl‐2‐pyrazolin‐5‐one which undergoes heterocyclization with α‐halogenated reagents at the more reactive phenylthiocarbamoyl moiety to afford the corresponding 4‐(thiazol‐2‐yl)‐1‐thiocarbamoyl‐2‐pyrazolin‐5‐ones. The new synthesized thiazolyl–pyrazolone compounds were evaluated for their potential antioxidant activity by using (ABTS Radical Cation Decolorization Assay).