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The highly versatile 6-cyano-5-oxo-3,5-dihydro-[1,2,4]triazolo[1,5- a ]pyrimidine ( 6 ) has been synthesized and utilized as a building block for the design of new tricyclic and tetracyclic ring systems incorporating the triazolo[1,5- a ]pyrimidine skeleton. The synthetic strategy for the construction of novel tricyclic classes, pyrazolo[4,3- e ]triazolo[1,5- a ]pyrimidines  7 – 8 , pyrido[3,4- e ]triazolo[1,5- a ]pyrimidines  9 – 10 , and pyrano[3,4- e ]triazolo[1,5- a ]pyrimidines  12 – 14 , based on reactions of the precursor  6  with hydrazines, activated nitriles, β-diketones, β-ketonitriles, and pyrazolones. The tetra-heterocyclic systems in which the pyrimido-[1,2,4]triazolo[1,5- a ]pyrimidine fused with different rings such as tetrazole, triazole, imidazole, and/or pyrazole were synthesized through the heterocyclization of the precursor  6  with various α-aminoazoles (namely; 5-amino-1 H -tetrazole, 3-amino-4 H -1,2,4-triazole, 2-aminobenzimidazole, 5-amino-3-methyl-1 H -pyrazole, and/or 5-amino-4-arylazo-pyrazoles). The newly synthesized polyheterocyclic ring systems were characterized by spectroscopic evidence, using IR,  1 H and 13C NMR, and mass analyses. The triazolo[1,5- a ]pyrimidine-based compounds were assayed for antioxidant properties by the ABTS technique to identify the tricyclic pyrano[3,4- e ]triazolo[1,5- a ]pyrimidine compounds  12a  and  12b  that exhibit the best antioxidant activity with percent inhibition (86.07% and 85.29%).

Synthesis of Polyheterocyclic Ring Systems Included Triazolo[1,5- a ]Pyrimidine as Antioxidant Agents