1,2,3-Triazolo[4,5-d]-1,2,4-triazolo[4,3-b]pyridazines

Some new 1,2,3-triazolo[4,5-d]-1,2,4-triazolo[4,3-b]pyridazines were prepared starting from the corresponding 1,2,3-triazolo[4,5-d]pyridazines via the formation of the 1,2,4-triazole ring, by condensation of an appropriate monocarbon fragment with the 4-hydrazino substituent and the nitrogen atom in the 5 position of the heterocycle. Condensation of 4-phenylhydrazino substituted derivatives with formic acid gave zwitterionic compounds.     

Synthesis of aromatic pyrazolo[4,5-b]pyridine derivatives

Cyclocondensation of chalcones with 5-amino-3-methyl-1-phenylpyrazole leads to the formation of 2,4-diaryl-5-methyl-7-phenyl-3,4-dihydropyrazolo-[4,5-b]pyridines, which undergo aromatization upon treatment with N-bromosuccinimide.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1247–1251, September, 1987.     

A facile one-step synthesis of chromeno[4,3-b]pyridine derivatives promoted by niobium pentachloride

Chromenes are part of an important class of heterocyclic compounds, natural or synthetic, and have many biological and chemical applications. Among them, chromenopyridines has arisen as a promising material for pharmacological applications. In this work is described a simple and cost-effective method to synthesize chromeno[4,3-b]pyridine derivatives from multicomponent reaction between 4-aminocoumarin, benzaldehyde derivatives, and ethyl benzoylacetates catalyzed by niobium pentachloride. The new method provides good yields with reasonable reaction times, under mild reaction conditions.     

The synthesis of 11H-1,2,4-triazolo[4,3-b]pyridazino[4,5-b]indoles,11H-tetrazolo[4,5-b]pyridazino[4,5-b]indoles and 1,2,4-triazolo[3,4-f]-1,2,4-triazino[4,5-a]indoles

This paper describes the synthesis of the previously unknown 11H-1,2,4-triazolo[4,3-b]pyridazino[4,5-b]indoles (2) and 11H-tetrazolo[4,5-b]pyridazino[4,5-b]indoles (3) from 4-hydrazino-5H-pyridazino[4,5-b]indoles (1) , as well as the synthesis of 1,2,4-triazolo[3,4-f]-1,2,4-triazino-[4,5-a]indoles (10) from 2-indolecarbohydrazide (4) . Compounds 2 were obtained by acylation of compounds 1 , followed of thermal cyclization and compounds 3 by treating compounds 1 with nitrous acid. The reactions of compound 4 with formic acid or ethyl orthoformiate gave 1,2-dihydro-1-oxo-1,2,4-triazino[4,5-a]indole (6) . Treating this last compound with phosphorus oxychloride or phosphorus pentasulfide, followed by hydrazine, gave 1-hydrazino-1,2,4-triazino-[4,5-a]indole (9) . Acylation of this last compound, followed of cyclization gave compounds 10 . All the compounds were characterized by elemental analysis and ir and ¹H-nmr spectra.     

Green synthetic approach toward new chromeno[4,3-b]quinoline and chromeno[4,3-b]pyridine derivatives

Chemistry of Heterocyclic Compounds - A facile, convenient, and efficient synthesis of new chromeno[4,3-b]quinoline and chromeno[4,3-b]pyridine derivatives has been accomplished via one-pot...     

The synthesis and transformations of 9H-imidazo[1,2-b]pyrazolo[4,3-d]-pyridazine and 9H-pyrazolo[4,3-d]-s-triazolo[4,3-b]pyridazine derivatives

The nucleophilic and electrophilic substitutions of 6-substituted 9,9-dimethyl-9H-imidazo[1,2-b]pyrazolo- [4,3-d]pyridazines 2 , nucleophilic substitutions of 6-substituted 9,9-dimethyl-9H-pyrazolo[4,3-d]-s-triazolo- [4,3-b]pyridazines 7 and some other transformations to give compounds 3 and 8 , respectively, were studied. It was shown that both heterocyclic systems are stable under the conditions employed in these transformations.     

Tandem aza-wittig reaction/electrocyclic ring-closure a facile entry to the synthesis of fused pyrimidines: Preparation of pyrazolo[3,4-d] and 1,2,3-triazolo[4,5-d]pyrimidine derivatives.

The aza-Wittig reaction of iminophosphoranes derived from 5-azido-4-formyl azoles, with isocyanates or carbon disulfide, leads to functionalized fused pyrimidines.     

Synthesis of 1,2,3-triazolo[1,5-a]pyridine ester derivatives

Lithiation of 1,2,3-triazolo[1,5-a]pyridines 4b and 4c with lithium diisopropylamide (LDA) gave the corresponding lithio derivatives 5b and 5c from which esters 6b and 6c were obtained by treatment with carbon dioxide and then dimethyl sulfate. Lithio derivatives 5a-5c reacted with DMF giving aldehydes 7a-7c. Esters 9a-9c were prepared from aldehydes 7a-7c and carbomethoxymethylenetriphenylphosphorane.     

Iminophosphorane-mediated efficient synthesis of new tricyclic 3,5-dihydro-1,2,3-triazolo[4,5-d]-1,2,4-triazolo[1,5-a]pyrimidin-9-ones

The carbodiimides 2, obtained from aza-Wittig reactions of iminophosphorane 1 with aromatic isocyanates, reacted with hydrazine to give selectively 6-amino-7H-1,2,3-triazolo[4,5-d]pyrimidin-7-ones 5. Compounds 5 were further transformed to iminophosphoranes 6 by reaction with triphenylphosphine, hexachloroethane and triethylamine. A tandem aza-Wittig reaction of iminophosphorane 6 with isocyanate or acyl chloride generated previously unreported 3,5-dihydro-1,2,3-triazolo[4,5-d]-1,2,4-triazolo[1,5-a]pyrimidin-9-ones 10 or 12 in satisfactory yield. X-ray structure analysis of 10 g verified the proposed structure and the reaction selectivity.     

Chemistry of furazano[3,4-b]pyrazine 6. 1,2,3-triazolo[4,5-b]furazano[3,4-b]pyrazines

The reduction of 1,2,3-triazolo[4,5-e]furazano[3,4-b]pyrazine 6-oxide was investigated. By means of data from x-ray crystallographic analysis it was shown that there is a relation between the aromaticity and the structure of the obtained triazoles.For communication 5, see [1].Latvian Institute of Organic Synthesis, Riga LV-1006. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1259–1264, September, 1998.     

A new and improved synthesis of 6-aryl-1,2,4-triazolo[4,3-b]pyridazines

A new and improved synthesis of 6-aryl-1,2,4-triazolo[4,3-b]pyridazines is described. This methodology provides the title compounds under mild conditions and in high yields. The first step comprises the condensation of an aryl methyl ketone with a 4-amino-1,2,4-triazole in toluene heated at reflux. The second step involves the condensation of that imine and t-butoxybis(dimethylamino)methane in tetrahydrofuran at ambient temperature. The third step constitutes the pyridazine ring closure to the title compounds in acetic acid heated at reflux.     

Synthesis of derivatives of a new heterocyclic system pyrazolo[3,4-b]pyrido[1′,2′: 1,2]imidazo[4,5-d]pyridine

1-[4-Aminoarylpyrazolo[3,4-b]pyridin-5-yl]pyridinium chlorides undergo cyclization under reflux in tert-butanol in the presence of an excess of potassium tert-butoxide to form tetracyclic derivatives of pyrazolo[3,4-b]pyrido[1′,2′:1,2]imidazo[4,5-d]pyridine. The reaction scheme of the processes is proposed. The structures of the reaction products were confirmed by physicochemical methods. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 710–714, April, 2006.     

Nitration of pyrazolo[4,3-b]quinolinones

The nitration of 1-methyl-4H-pyrazolo[4,3-b]quinolin-9-one and some of its derivatives with nitric acid in sulfuric acid and acetic anhydride was studied. It was established that the number and site of incorporation of the nitro groups depends on the nature of the attacking agent, the reaction conditions, and the substituents present in the molecule.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1084–1089, August, 1985.     

Tautomerism of some imidazo[4,5-b]pyridine derivatives

It was shown by means of UV and IR spectroscopy and the ionization constants that the tautomeric equilibrium of 2-amino- and 2-mercapto derivatives of 3-methyl-3H-imidazo[4,5-b]pyridine is shifted to favor the amino and thione forms, respectively.     

Synthesis and antituberculotic activity of some new imidazo[4,5-b]pyridine derivatives

The reactions of 2-acetylimidazo[4,5-b]pyridine hydrazone with some alkyl-and arylisothiocyanates and some orthoesters were carried out. Various new derivatives of the titled compound such as thiosemicarbazones, ethoxymethylenehydrazones, and derivatives of the new pyrido-[3′,2′:4,5]imidazo[1,2-d][1,2,4]triazine ring system were obtained. Biological data for selected compounds are presented. Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1571–1579, October, 2006.     

Cyclization of substituted 2,3-diaminopyridines into derivatives of 1H-1,2,3-triazolo[4,5-b]pyridine 2-oxide in the course of nitration

Russian Journal of Organic Chemistry -