Cyclization of N-alkylazinium cations with bifunctional nucleophiles. 22. Crystal and molecular structure of tetrahydroquinoxaline condensed with the six-membered 1,3,4-thiadiazine ring

X-ray diffraction examination of 4-acetyl-10-methyl-2-phenyl-1,4,4a,5,10,10a-hexahydro-1,3,4-thiadiazino[5,6-b]quinoxaline has shown that the 4a-H and 10a-H hydrogens attached to the carbon atoms common to both heterocycles are cis-oriented, as in the annelation of five-membered heterocycles to the tetrahydropyrazine ring, but in this case the torsion angle H_(4a)C_(4a)C_(10a)H_(10a) is much greater, having a value of 60.For Communication 21, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 701–706, May, 1987.     

Cyclization of N-alkylazinium cations with bifunctional nucleophiles. 24. Synthesis of condensed 1,2,4-triazino- and 1,2,4-oxadiazino[5,6-b]quinoxaline systems

Cyclization of quinoxalinium salts with amidoximes and amidhydrazones yields partially hydrogenated derivatives of new 1,2,4-oxadiazino- and 1,2,4-triazino[5,6-b]quinoxaline heterocyclic systems.For Communication 23, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1118–1121, August, 1987.     

Cyclization of N-alkylazinium cations with bifunctional nucleophiles. 23. Electrochemical criteria for electrophilicity in 1,4-diazinium cations and their participation in cyclizations with acetoacetamide

The polarographic reduction potentials E_1/2 of the pyrazinium, quinoxalinium, benzoquinoxalinium, pyrido[2,3-b]pyrazinium, and pteridinium cations were determined. Annellation of a benzene ring increases the electrophilicity of the diazinium cations to a greater degree than the introduction of such electron acceptors as aza, aminocarbonyl, or methoxycarbonyl groups. The boundary between the active and inactive 1,4-diazinium salts was determined; cations with E_1/2 values more negative than –0.50 V do not form either stable covalent adducts or cyclic diadducts through annellation of the dinucleophiles to the pyrazine ring.For Communication 22, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1110–1117, August, 1987.     

Cyclization of azines with bifunctional nucleophiles — a one-step route to condensed heterocycles (review)

Nucleophilic diaddition and disubstitution in the azine. series with the participation of bifunctional reagents, the result of which is the formation of condensed heterocycles, were examined.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1011–1026, August, 1985.     

Cyclization of N-alkylazinium cations with bifunctional nucleophiles. 14. Reaction of quinoxalinium salts with mono- and N,N′-disubstituted amidines

Monosubstituted benzamidines undergo cyclization with quinoxalinum salts to give 1,2-disubstituted 3a,4,9,9a-tetrahydroimidazo[4,5-b]quinoxalines. The participation in similar cyclizations of N,N-disubstituted amidines with a CH-active group in the a position leads to 3a,4,9,9a-tetrahydropyrrolo[2,3-b]quinoxalines.See [1] for Communication 13.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 390–395, March, 1985.     

Cyclization of N-alkylazinium cations with bifunctional nucleophiles. 15. Isomerization of thiazolo[4,5-b]quinoxalines in the presence of acids

4-Alkyl-2-phenyl-3a,4,9,9a-tetrahydrothiazolo[4,5-b]quinoxalines undergo isomerization in chloroform in the presence of acids to the regioisomeric (with respect to them) 9-alkyl-substituted derivatives. Under the same conditions 2,4-dimethyl-3a,4-9,9a-tetrahydrothiazolo [4,5-b]quinoxaline undergoes isomerization to 4-methyl-1H-2,3,3a,4,9,9a-hexahydropyrrolo[2,3-b]quinoxaline-2-thione. It was demonstrated by means of deuterium labels that in both cases the isomerization proceeds through a step involving dissociation to a quinoxalinium cation and the corresponding thioamide.See [1] for Communication 14.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 396–403, March, 1985.     

Cyclization of N-alkylazinium cations with bifunctional nucleophiles. 10. Isomeric thiazolo[4,5-b]quinoxalines in reactions of N-methylquinoxalinium ions with dithiocarbamates

The cyclization of N-methylquinoxalinium iodide with ammonium salts of N-alkyl-dithiocarbamic acids in DMSO leads to 4-methyl-2,3,3a,4,9,9a-hexahydrothiazolo-[4,5-b]quinoxalines, whereas regioisomeric cycloadducts with a reversed orientation of the thiazole ring are formed in ethanol in the presence of diethylamine.See [1] for communication 9.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 680–685, May, 1984.     

Cyclization of N-alkylazinium cations with bisnucleophiles. 6. Cycloelimination of tetrahydro-endo-furo[2,3-b]quinoxalines leading to 2,3-disubstituted tetrahydroquinoxalines

The reaction of an N-methylquinoxalinium salt with a -diketone under thermodynamic-control conditions leads to 2,3-disubstituted tetrahydroquinoxaline via cycloelimination of the initially formed tetrahydro-endo-furo[2,3-b]quinoxaline.See [1] for communication 5.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1410–1416, October, 1982.     

Cyclizations of N-alkylazinium cations with bifunctional nucleophiles. 18. Synthesis and structure of heterocyclic systems based on quinoxaline

N-Methylquinoxalinium iodide reacts with ethylenediamine, o-phenylenediamine, and o-aminophenol to give cyclization products of the type involving [2,3-b] annelation of the six-membered heteroring. Two molecules of the quinoxaline participate in the cyclization with 2-aminoethanol to give a complex polycyclic compound.See [1] for communication 17.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1116–1124, August, 1985.     

Cyclization of N-alkylazinium cations with binucleophiles. 8. Annellation of the imidazole ring with pyrazines and quinoxalines

Monosubstituted and N,N′-disubstituted thioureas enter into cyclization with pyrazinium and quinoxalinium ion to form imidazo[4,5-b]-annellated pyrazines and quinoxalines.     

Cyclization of N-alkylazinium cations with bifunctional nucleophiles. 29. Synthesis of a novel 1,3,4-thiadiazolo-[2,3-a]quinoxalino[2,3-d]pyrrole heterocyclic system

1,4,4a,5,10,10a-Hexahydro-1,3,4-thiadiazino[5,6-b]quinoxalines react with acetylacetone and acetoacetate esters upon heating in ethanol to give derivatives of a novel heterocyclic system, hexahydro-1,3,4-thiadiazolo[2,3-a]quinoxalino[2,3-d]pyrrole.For Communication 28, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 697–702, May, 1990.     

Cyclization of N-alkylazinium cations with bifunctional nucleophiles. 11. Reactions of quinoxalinium salts with thioamides — Simple method for the synthesis of hydrogenated thiazolo[4,5-b]quinoxalines

Thioacetamides and thiobenzamides undergo cyclization with N-alkylquinoxalinium salts in the presence of bases to give 4-alkyl-3a,4,9,9a-tetrahydrothiazolo[4,5-b]quinoxalines.See [1] for communication 10.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 686–690, May, 1984.     

Cyclization of N-alkylazinium cations with bifunctional nucleophiles. 16. σ-adducts of quinoxalinium salts with amines,alcohols, and enolates and their role in cyclizations with β-dicarbonyl compounds

In the reaction of N-methylquinoxalinium iodide with acetylacetone at –30 °C, the formation of 3-acetyl-2,4-dimethyl-3a,4,9,9a-tetrahydrofuro[2,3-b]quinoxaline has been recorded by ¹H NMR spectroscopy, this being a regioisomer of the 3-acetyl-2,9-dimethyl-3a,4,9,9a-tetrahydro[2,3-b]quinoxaline formed in this reaction at temperatures above –10 °C. -Adducts of the N-methylquinoxalinium cation with alcohols, amines, and -diketones have also been identified, and their role in cyclizations leading to the annelation of a furan ring is discussed.For Communication 15, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 669–677, May, 1985.     

Cyclization of N-alkyl azinium cations with bifunctional nucleophiles. 21. Regioisomeric 1,3,4-thiadiazino[5,6-b]quinoxalines

Thiobenzhydrazides undergo cyclization with N-alkyl-quinoxalinium salts to give 5-alkyl-substituted 1,4,4a,5,10,10a-hexahydro-1,3,4-thiadiazino[5,6-b]quinoxalines, which undergo isomerization to 10-alkyl-substituted thiadiazinoquinoxalines when they are heated in ethanol or in the presence of acids.See [1] for Communication 20.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 557–561, April, 1987.     

Cyclizations of N-alkylazinium cations with bifunctional nucleophiles. 19. Crystal structure of the kinetic product of the reaction of N-methylquinoxalinium iodide with thioacetamide

The mutual orientation of the heterorings and the three-dimensional structure of the kinetic product of the reaction of N-methylquinoxalinium iodide with thioacetamide were established by x-ray diffraction analysis of 2,4-dimethyl-9-acetyl-3a,4,9,9a-tetrahydrothiazolo [4,5-b]quinoxaline.See [1] for communication 18.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1417–1421, October, 1985.     

Reactions of N-alkylazinium cations. 3. Quaternary pteridinium salts. Synthesis,structure, and reactions with simple nucleophiles

4-Morpholinopteridine reacts with triethyloxonium tetra-fluoroborate to give two types of isomeric quaternary salts, viz., 1-ethyl- and 8-ethyl-4-morpholinopteridinium tetrafluoroborates. The structures of the pteridinium cations were proved by the ¹H and ¹³C NMR spectra and also by chemical transformations in reactions with simple nucleophiles.See [1] for communication 2.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1257–1264, September, 1985.     

Cyclization of N-alkylammonium cations with bifunctional nucleophiles. 17. Annelation of imidazole and 1,2,4-triazine rings with pyrazines via the reactions of thiosemicarbazides with pyrazinium salts

1- and 4-mono- as well as 1,4-disubstituted thiosemicarbazies undergo cyclization reactions upon treatment with N-alkylpyrazinium and quinoxalinium salts to give N-aminosubstituted imidazo[4,5-b]pyrazines and imidazo[4,5-b]quinoxalines, respectively. Thiosemicarbazides containing substituents in the 2-position react with N-alkylquinoxaline salts to give 1,2,4-triazino[5,6-b]quinoxalines after cyclization.For communication No, 16, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 960–966, July, 1985.     

Application of 1H and 13C NMR to the structural elucidation of tetrahydroquinoxalines condensed with five-membered heterocycles

¹H and ¹³C NMR spectral data for 21 N-methyltetrahydroquinoxalines annelated with furan, pyrrole, imidazole or thiazole rings are reported. Unambiguous assignments of the ring junction ¹³C resonances were made on the basis of selective decoupling experiments and with the aid of one-bond and long-range ¹³C–¹H coupling constants. The effects of five-membered heterocycles on the ¹H and ¹³C chemical shifts of the ring junction hydrogen and carbon atoms are considered. Values of one-bond ¹J(CH) and vicinal ³J(HH) coupling constants between the ring junction protons are also discussed as a diagnostic means for structural elucidation of tetrahydroquinoxalines condensed with five-membered heterocycles.