1,3-Disubstitutedpyrazole-4-caboxaldehyde in Heterocyclic Synthesis: A Novel Synthesis of Pyridine-2(1H)-thione and Fused Nitrogen and/or Sulfur Heterocyclic Derivatives

Pyridine-2(1H)-thione 5 was synthesized from the reaction of 3-3-(4-chlorophenyl)-1-phenyl-1H-pyrazol-4-yl]-1-phenylpropenone (3) and cynothioacetamide (4). Compound 5 reacted with halogented compounds 6a–e to give 2-S-alkylpyridine derivatives 7a–e, which could be in turn cyclized into the corresponding thieno2,3-b]-pyridine derivatives 8a–e. Compound 8a reacted with hydrazine hydrate to give 9. The latter compound reacted with acetic anhydride (10a), formic acid (10b), acetic acid, ethyl acetoacetate, and pentane-2,4-dione to give the corresponding pyrido3′,2′:4,5]thieno-3,2-d]pyrimidine 13a,b, pyrazolo3′,4′:4,5]thieno3,2-d]pyridine 14 and thieno2,3-b]-pyridine derivatives 18 and 20, respectively. Alternatively, 8c reacted with 10a,b and nitrous acid to afford the corresponding pyrido3′,2′:4,5]thieno3,2-d]pyrimidine 24a,b and pyrido3′,2′:4,5]thieno3,2-d]1,2,3]triazine 26 derivatives, respectively. Finally compound 5 reacted with methyl iodide to give 2-methylthiopyridine derivative 27, which could be reacted with hydrazine hydrate to yield the corresponding pyrazolo3,4-b]-pyridine derivative 29.