Bicyclic [b]‐heteroannulated pyridazine derivatives. 9. cyclization reactions of 4,4‐dimethyl‐ and 4‐phenyltetrahydropyridazine‐3,6‐dione 3‐hydrazones with esters of keto dicarboxylic acids

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

Crystal structure of 1,1,5,5-tetramethyl-1,2,5,6-tetrahydro-3a,4,7a,8-tetraaza-s-indacene-3,7-dione, C12H16N4O2

“…Two weak intermolecular interactions, ¿(C8-H-03") = 3.489(2) Â and rf(C9-H-03'") = 3.362(2) Â, respectively, classified as weak H-bonds [6], were found in the crystal (ii = 2-x, 1-y, 1-z; Hi: 2-x, 1/2 +y, 3/2-z). (7) 0.011 (1) …”

“…Continued investigations on the formation of bicyclic [b]-annulated pyridazine derivatives from 4,4-dimethyltetrahydropyridazine-3,6-dione 3-hydrazone [1] required repeated and upscaled preparation of this compound in the reaction of a 3-cyano-3-methylbutyric ester with hydrazine hydrate [2]. A thorough reexamination of the latter reaction made it possible to isolate the title compound which was formed in minute amounts as a by-product [3].…”

Chemistry of α-Oxoesters: A Powerful Tool for the Synthesis of Heterocycles

“…Also, the synthesis of pyridazino-triazines was reported using a similar methodology, as in 2001, Wejroch et al described the reaction of 6-hydrazinyl-4,5-dihydropyridazin-3­(2 H )-one 609 with α-oxoesters in EtOH at room temperature, to yield the corresponding hydrazones, which could be converted to 3-substituted 8,9-dihydro-4 H -pyridazino­[6,1- c ]­[1,2,4]­triazine-4,7­(6 H )-diones 610 when heated at 160–210 °C under solvent-free conditions. Additionally, one-step cyclocondensation reactions were performed by refluxing a mixture of 609 and α-oxoesters in EtOH (Scheme a).…”

Synthesis of heterocyclic compounds using oxaloacetic ester (review)

“…7-Aminopyrimido- [4,5- The triazepine derivative 92 can be obtained from anthranilohydrazide [40], whereas only the corresponding 2-nitrophenylhydrazones 94a,b are formed from substituted 2-nitrophenylhydrazines 93a,b [41]. Derivatives of 3-hydrazinotetrahydropyridazine-3,6-dione (95) react readily with oxaloacetic ester with the formation of bis(ethoxycarbonyl)alkylidene derivatives 96 [42]. The condensation product can exist both in the enamine form 96a and in the imine form 96b, and further cyclization by boiling in alcohol leads to the formation of compounds 97 and 98.…”