S. A. Shipilovskikh, A. Rubtsov
Jan 8, 2015
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0
Influential Citations
11
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Journal
Russian Journal of Organic Chemistry
Abstract
As we showed previously, 5-arylfuran-2,3-diones react with hydrazines to give 4-aryl-2,4-dioxobutanoic acid hydrazides [1–3]; however, introduction of a substituent into the 4-position of the furan ring changes the reaction direction toward formation of cyclic products, in particular pyridazin-3-ones [4–10] and pyrazolecarboxylic acid derivatives [4, 7–12]. On the other hand, replacement of the carbonyl oxygen atom in the 3-position by =CH2 group leads to the formation of both acyclic products, acrylic acid hydrazides [13–15], and pyridazin-3-one derivatives [13–16]. The goal of the present work was to study the reaction of hydrazines with 5-arylfuran-2,3-dione analogs in which the 3-oxo group is replaced by 3-ethoxycarbonylthiophen2-ylimino. We previously found that the reaction of hydrazines with 5-aryl-3-(1,5-dimethyl-3-oxo-2phenyl-1,2-dihydro-3H-pyrazol-4-ylimino)-3H-furan2-ones is governed by the substituent nature in the hydrazine and that the products are 3-iminopyrrol-2ones or pyridazin-3-ones [17–19]. Interest in this reaction is determined by the fact that some transformation products displayed various kinds of biological activity [2, 3, 10–13, 19]. Furthermore, introduction of a Gewald thiophene fragment [20–23] was expected to increase the probability of revealing biological activity of the products. The reactions of ethyl 2-[2-oxo-5-phenylfuran3(2H)-ylideneamino]-4,5,6,7-tetrahydro-1-benzothiophene-3-carboxylate (I) with hydrazines IIa–IId in an inert aprotic solvent resulted in the formation of the corresponding ethyl 2-(3-oxo-6-phenyl-2-R-2,3-dihydropyridazin-4-ylamino)-4,5,6,7-tetrahydro-1-benzothiophene-3-carboxylates IIIa–IIId which were isolated as crystalline substances. Presumably, as in the reaction of compound I with amines, initial attack by the amino nitrogen atom of the hydrazine molecule on the carbonyl carbon atom in the dihydrofuran ring induces opening of the furan ring at the C–O bond [24]. The subsequent attack by the second nitrogen atom on the C=O carbonyl carbon atom of intermediate 4-oxo-4phenyl-2-[3-(ethoxycarbonyl)-4,5,6,7-tetrahydro-1benzothiophen-2-ylamino]but-2-enehydrazide leads to pyridazine ring closure with formation of 4-imino-6phenyl-1,2-dihydro-4H-pyridazin-3-one derivatives, and [1,5]-prototropic shift in the latter yields thermodynamically more stable isomer III. Ethyl 2-(3-oxo-6-phenyl-2,3-dihydropyridazin4-ylamino)-4,5,6,7-tetrahydro-1-benzothiophene3-carboxylate (IIIa). Hydrazine hydrate (IIa), 0.05 g (1 mmol), was added to a solution of 0.381 g (1 mmol) of compound I in 3 mL of anhydrous toluene, and the mixture was heated for 30 min to the boiling point.