No abstract

Bis(ethoxycarbonyl)alkylidene derivatives 4 and 5 of the respective title hydrazones were obtained in the reactions with diethyl oxomalonate, diethyl oxosuccinate, diethyl 2-oxoglutarate, and diethyl oxalopropionate as mixtures of geometric isomers with high predominance of one of them. On heating at 160-200°without any solvent or on refluxing in ethanol 4 cyclized to yield the corresponding pyridazino[6,1-c]triazines 6, whereas heating of 5 gave, depending on the chain length, the corresponding pyrazolylpyridazines 8b and 8d or the pyridazinylpyridazine 8c. X-ray analysis was used to determine the structures of 6 and 8; the unit cell of 6c was found to accommodate 16 molecules representing four conformational varieties. The different behavior of 4 and 5 in the cyclization reactions was interpreted in terms of the tautomeric equilibrium which was shifted towards the enamine form in 4, and towards the imine form, in 5. Transmission of a long-range chirality effect in 4d and 5a-d manifested itself in the 1 H nmr spectra as the magnetic non-equivalence of the CH 2 protons in one or both ester ethyl groups. The 4-substituted tetrahydropyridazine-3,6-dione 3-hydrazones, readily available in the reaction of the appropriately 3-substituted 3-cyanopropionic esters with hydrazine hydrate [2], have been found earlier to be interesting and versatile starting materials in the preparation of bicyclic structures. Thus, the triazolo[4,3-c]pyridazine core was formed in the reaction with trifluoroacetic acid [3], whereas pyridazino[6,1-c]triazine derivatives were obtained in that with α-keto esters [4]. In either case, the intermediate linear acylation or condensation products underwent a spontaneous or enforced intramolecular cyclocondensation via the N2 pyridazine atom. With the most simple β-keto ester, ethyl acetoacetate, and some 4-aryltetrahydropyridazine-3,6-dione 3-hydrazones the cyclocondesation reaction run a different course to yield the derivatives of pyrazolylpyridazine formed by attack on the exocyclic (hydrazine) nitrogen atom [4].Considering the distinction in the behavior of α-and β-keto esters we report now on the reactions of two tetrahydropyridazine-3,6-dione 3-hydrazones, namely their 4,4-dimethyl-(1) and 4-phenyl-substituted (2) derivatives, with esters of dicarboxylic keto acids in which the keto function is α relative to one, and α, β, or γ, to the other ester group. The main aim of the research was to find out which cyclocondensation pattem would predominate in the case when two ester groups were available. It was also expected that the easily convertible alkoxycarbonyl function in the bicyclic reaction products might tum out to be useful in the synthesis of compounds with potential biological activity.Both 1 and 2 reacted in an ethanol solution with diethyl oxomalonate (3a), diethyl oxosuccinate (3b), diethyl 2-oxoglutarate (3c), and diethyl oxalopropionate (3d) to 877

C12H16N4O2, monoclinic, Pillici (No. 14), a = 9.306(2) Á, b = 5.755(1) Â, c = 11.499(2) λ, β = 98.15(3)°, V= 609.6 À 3 , Z = 2, R gt (F) = 0.045, wRrtiF 2 ) = 0.075, T= 294 K.

: Nitrogen NMR shieldings (*p \ [d on the frequency scale of chemical shifts), measured by highprecision 14N NMR and bulk susceptibility corrected, of 20 nitroalkanes in dilute solutions in cyclohexane and in acetone are reported, including vic-dinitro, gem-dinitro and trinitro structures and tetranitromethane. The data obtained for cyclohexane solutions yield an excellent linear correlation with theoretical shieldings calculated for the corresponding isolated molecules by the semi-empirical TNDO/2 method. The nitrogen shieldings of nitro-NO 2 alkanes are shown to depend linearly on the net charges of the corresponding nitro groups, each taken as a whole, but there is no correlation with the atomic charges of the nitrogen atoms concerned. Thus, the nitrogen shieldings seem to provide a measure of electron-acceptor or electron-donor strength of the substituted alkyl system bound directly to the nitro group. Solvent polarity e †ects on the shieldings are discussed. The nitro group nitrogen shieldings are shown to be generally sensitive to conformational e †ects, particularly in sterically hindered molecules, and to provide insight into conformational or rotamer equilibria in nitroalkane systems. Ab initio calculations of the shieldings of some simple nitroalkanes, using the HartreeÈFock/GIAO approach, are reported. They indicate that the semi-empirical method employed, combined with the experimental data, yields results which are comparable to those obtained by the ab initio method, as far as relative shieldings are concerned.

Other 6-membered heterocycles R 0670 Reaction of β-Cyano Esters with Hydrazine Hydrate. Unexpected Formation of Dipyrrolo[1,2-b:1',2'-e][1,2,4,5]tetrazine, a Novel Ring System. -Reactions of the title cyano esters (I) with hydrazine hydrate provides pyridazinone derivatives (II), (IV), disymmetric azines (III) and/or the title dipyrrolotetrazine (V) depending on the molar ratio of reagents and the reaction conditions. -(WEJROCH, K.; WESOLOWSKA, A.; SADOWSKA, M.; KAROLAK-WOJCIECHOWSKA, J.; JAGODZINSKI, T.; LANGE*, J.; J. Heterocycl. Chem. 42 (2005) 5, 919-924; Dep. Chem., Warsaw Univ. Technol., PL-00-664 Warszawa, Pol.; Eng.) -A. Forchert 47-164