UTILITY OF N-2-PYRIDYL–3-OXOBUTANAMIDE IN HETEROCYCLIC SYNTHESIS: SYNTHESIS OF NEW DIHYDROPYRIDINE, FUSED PYRIDINE, PYRIDOPYRIDONE, PYRIDAZINE AND PYRIDOPYRIMIDINETHIONE DERIVATIVES

Abstract

2-Aminopyridine was fused with ethyl acetoacetate for two hours to yield the N-2-pyridyl–3-oxobutanamide (1). However, when the reaction time was increased to 5 hours compound 3 was obtained. Condensation of 3 with benzaldehyde gave 4. The reaction of pyridopyridone 3 with arylidenemalononitrile 7a-c afforded 4H-pyran derivatives 10a-c. In contrast to the behavior of arylidenemalononitriles 7a-c towards pyridopyridine 3, benzylidenemalononitrile 7d reacted with compound 3 to give the product 11. Compound 1 was allowed to react with arylidenemalononitriles to give the dihydropyridine derivatives 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 benzoyl isothiocyanates 25a,b to give thiourea derivatives 26a,b. Cyclization of 26a,b in dry dioxane and conc. sulphuric acid afforded pyridopyrimidine-2-thione derivatives 27a,b. On the other hand, coupling of pyridopyridone 3 with the aryl diazonium salts 28a-e afforded the corresponding azo products 29a-e. Boiling of compound 29 in ethanol and HCl afforded the azo products 30a-e. Treatment of arylhydrazone 30a with malononitrile afforded the pyridazine derivative 31.