Heterocyclic compounds containing nitrogen and sulfur have attracted considerable attention due to widespread application of their pharmacological activities. Pyrimidine and its derivatives play a vital role in the field of drugs and agricultural chemicals. Derivatives of the pyrimidine system are of course essential to the structure of DNA and RNA. 1 Pyrimidine derivatives are of interest due to their pharmacological properties such as antitumour, 2-6 antiviral, 7 antifungal, anticancer, 8 antibacterial, 9 anti-inflammatory, 10-13 analgesic, 14 antagonist, 15,16 antifolate, 17 antimicrobial, 2 antiproliferative, 18 antiplatelet, antithrombotic 19 and antioxidant 20,21 activities.In addition, triazolopyrimidines are versatile ligands and their derived coordination compounds can be considered as model systems for metal-ligand interactions observed in biological systems. [22][23][24] Due to the aforementioned facts concerning triazolopyrimidines and in continuing efforts to find more potent and selective antioxidant compounds, here we have synthesised triazolopyrimidines, pyrimidotriazines and non-fused heterocyclic systems such as pyrazole and dioxopyrazolidine derivatives. Results and discussionAs a continuation of our previous work 2,20,21,25,26 on the utility of activated nitriles in the synthesis of a wide variety of heterocyclic systems, in this work we aimed to design and construct pyrimidine derivatives from relatively simple starting materials. Thus,3]dioxol-5-yl)-4-oxo-2-thioxo-1,2,3,4tetrahydropyrimidine-5-carbonitrile (1) was prepared by condensation of thiourea with ethyl 3-(benzo [d][1,3]dioxol-5yl)-2-cyanoacrylate in refluxing ethanol. 27 Hydrazinolysis of the tetrahydropyrimidine 1 afforded the sulfur-free compound which was identified as 4- 27 Recently, we have reported 25 that hydrazino pyrimidines can be considered as key starting materials for the synthesis of diverse nitrogen bridgehead compounds. This prompted us to reinvestigate the reactivity of compound 2 with some electrophilic reagents with the aim of preparing new fused and non-fused heterocyclic compounds which might have chemotherapeutic and biological value.Acetylation of hydrazinopyrimidine derivative 2 using freshly distilled acetic anhydride yielded the diacetylhydrazinopyrimidinyl acetate 3. The IR spectrum of this compound displayed bands corresponding to n NH , ν C≡N , n C=O ester and n