BICYCLIC [B]-HETEROANNULATED PYRIDAZINE DERIVATIVES .4. CYCLIZATION REACTIONS OF 4-ARYLTETRAHYDROPYRIDAZINE-3,6-DIONE 3-HYDRAZONES WITH SOME KETO ESTERS
J. Lange et al., BICYCLIC [B]-HETEROANNULATED PYRIDAZINE DERIVATIVES .4. CYCLIZATION REACTIONS OF 4-ARYLTETRAHYDROPYRIDAZINE-3,6-DIONE 3-HYDRAZONES WITH SOME KETO ESTERS, Journal of heterocyclic chemistry, 34(2), 1997, pp. 389-396
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.