Utility of N-2-pyridyl-3-oxobutanamide in heterocyclic synthesis: Synthesis of new dihydropyridine, fused pyridine, pyridopyridine, pyridazine and pyridopyrimidinethione derivatives

2-Aminopyridine was fused with ethyl acetoacetate without solvent for two hours to yield the  N-2-pyridyl–3-oxobutanamide 1. However, when the reaction time was increased to 5 hours a structure 3 was obtained. Condensation of the structure 3 with benzaldehyde gave 4. The reaction of pyridopyridone 3 with arylidenemalononitrile7a-c afforded 4 H-pyran derivative 10a-c. In contrast to the behavior of arylidenemalononitrile 7a-c towards pyridopyridine3, benzylidenemalononitrile 7d reacted withcompound 3 to give a product 11. Compound 1 was allowed to react with arylidenemalononitrile to give the dihydropyridine derivative 17a-d. Alkylation of compound 1 with alkylating agents has been also reported. Thus, compound 1 was condensed with [DMF-DMA] in refluxing dioxane to yield 18, but under the reaction conditions we obtained only 21. The pyridopyridone 3 reacted with benzoylisothiocyanate 25a,b to give thiourea derivatives 26a,b Cyclization of 26a,b in dry dioxane and conc. sulphuric acid afforded pyridopyrimidinethione derivatives 27a,b. On the other hand, coupling of pyridopyridine 3 with the aromatic diazonium salt 28a-e afforded the corresponding azo products 29a-e. Boiling of compound 29 in aqueous solution of HCl afforded the hydrazo products 30. Treatmentof arylhydrazone 30a with malononitrile afforded the pyridazine derivatives 31.