Synthesis and Antioxidant Activity of New Pyrazolo[1,5-a]Pyrimidine Derivatives Incorporating a Thiazol-2-yldiazenyl Moiety

4-(Thiazol-2-yldiazenyl)-1H-pyrazole-3,5-diamine (2) was prepared by the reaction of 2-thiazolylazomalononitrile (1) with hydrazine hydrate in boiling ethanol and used as key intermediate for the synthesis of polyfunctionally substitut ed pyrazolo[1,5-a]pyrimidines via its reactions with reagents having 1,3-dielectrophilic centers. Structures of the newly synthesized compounds were established by elemental analysis and spectral data. Representative compounds of the synthesized products were tested and evaluated as antioxidant agents. The results revealed that compounds (3), (4), (5), and (9) displayed promising antioxidant activity compared to the activity of ascorbic acid.