Pyrido[2,3-d]pyrimidine-2,7-dithiol in heterocyclic synthesis: Synthesis and characterization of several new fused pyridopyrimidine heterocycles

Pyridine-2(1H)-thione 1 reacted with phenyl isothiocyanate to give pyrido2,3-d]pyrimidine derivative 3. Compound 3 reacted with halogen containing compounds 4a–d and methyl iodide in dimethylformamide/potassium hydroxide solution at room temperature to give 2,7-bisalkylthiopyrido2,3-b]pyrimidine derivatives 5a–d and 9, respectively. Compounds 5a–d could be cyclized into thienopyrido2,3-d]pyrimidine derivatives 6a–d by boiling with ethanolic potassium hydroxide solution. Compound 6a reacted with acetic anhydride or formic acid and gave the corresponding pyrimido4″,5″:4′,5′]thieno3′,2′:5,6]pyrido2,3-d]pyrimidine derivatives 8a,b. Compound 9 reacted with hydrazine hydrate to yield pyrazolo4′,3′:5,6]pyrido2,3-d]pyrimidine derivative 11 which could be reacted with nitrous acid and dimethylformamide-dimethylacetal (DMF-DMA) and gave the final isolable products corresponding to the pyrazolo4′,3′:5,6]pyrido2,3-d]tetrazolo-5,1-b]pyrimidine and pyrimido1″,2″:1′,5′]pyrazolo4′,3′:5,6]pyrido2,3-d]1 Abbas, A. A., Elneairy, M. A.A. and Mabkhot, Y. N. 2001. J. Chem. Res.(S), 4: 124Crossref] , Google Scholar] 2 Riad, B. Y., Negem, A. M., Abdou, S. E. and Daboun, H. A. 1987. Heterocycles, 26: 205Crossref], Web of Science ®] , Google Scholar] 4 Gad-Elkareem, M. A.M. and Abedelhamid, A. O. 2004. Afinidad, 61(513): 427Web of Science ®] , Google Scholar]triazolo-4,3-b] pyrimidine derivatives 13 and 17, respectively. Compound 11 also reacted with some β-dicarbonyl compounds such as acetylacetone (18) and ethyl acetoacetate (20) to yield the corresponding pyrimido1″,2″:1′,5′]pyrazolo4′,3′:5,6]pyrido2,3-d]pyrimidine derivatives 19 and 21, respectively. Finally, compound 11 reacted with chloroacetyl chloride (22) to give the corresponding imidazo1″′,2″′:1″,5″]pyrazolo4″,3″:5′,6′]pyrido3′,2′:5,6]pyrimido2,1-c]1 Abbas, A. A., Elneairy, M. A.A. and Mabkhot, Y. N. 2001. J. Chem. Res.(S), 4: 124Crossref] , Google Scholar] 2 Riad, B. Y., Negem, A. M., Abdou, S. E. and Daboun, H. A. 1987. Heterocycles, 26: 205Crossref], Web of Science ®] , Google Scholar] 4 Gad-Elkareem, M. A.M. and Abedelhamid, A. O. 2004. Afinidad, 61(513): 427Web of Science ®] , Google Scholar]triazine derivative 23.