BICYCLIC [B]-HETEROANNULATED PYRIDAZINE DERIVATIVES .4. CYCLIZATION REACTIONS OF 4-ARYLTETRAHYDROPYRIDAZINE-3,6-DIONE 3-HYDRAZONES WITH SOME KETO ESTERS

Ethoxycarbonylalkylidene derivatives 2 and 6 of the title hydrazones w ere obtained in the reaction with ethyl pyruvate or ethyl aroylformate and ethyl acetoacetate, respectively, in methanol. Both compounds wer e mixtures of geometric isomers with high predominance of one of them. Nmr spectroscopy revealed an unexpected magnetic non-equivalence of t he CH2 protons in the ester ethyl group of the major isomer of 6. On h eating (similar to 200 degrees) in an inert medium or on refluxing in ethanolic sodium ethoxide 2 cyclized to the corresponding pyridazino[6 ,1-c]triazines 4, whereas 6 formed pyrazolylpyridazines 7. The structu re of the latter was unambigously established by X-ray analysis. Alkyl ation of 4a with benzyl bromide in the presence of tetrabutylammonium bromide occurred selectively on the pyridazine N atom.