Abstract
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-1H-tetrazole, 3-amino-4H-1,2,4-triazole, 2-aminobenzimidazole, 5-amino-3-methyl-1H-pyrazole, and/or 5-amino-4-arylazo-pyrazoles). The newly synthesized polyheterocyclic ring systems were characterized by spectroscopic evidence, using IR,
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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%).