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.     

Protolytic Equilibrium of the Isomeric Phenyl-1,2,4-triazines

The protonation constants for the first and second stages (pK_BH+, pK_BH2+) of a series of 1,2,4-triazines with a phenyl substituent at various positions in the ring were determined in aqueous solution by a spectrophotometric method. The values of the basicity constants characterizing the first protonation of the heterocycles investigated was in the range of acidity of the medium of pH 3.5 to H ₀ -2, and the second from H ₀ -7.3 to H ₀ -8.7. The position of the phenyl substituent proved to have a significant effect on the size of pK_BH+. According to the results of ab initio calculations using HF/6-31G** for the heterocycles investigated the 1H⁺ form is thermodynamically most stable among the monocations, with the exception of 6-phenyl-1,2,4-triazine for which the existence of the monocation in the 1H⁺ and 2H⁺ forms are equally probable. In the case of the dications of all the triazines the 2,4-H,H²⁺ tautomer is the most preferred. The aromaticity of the 1,2,4-triazine ring is changed insignificantly on mono- and diprotonation.     

Reactions of [60]fullerene with 2-azidopyrimidines

The reaction of [60]fullerene with 2-azidopyrimidines affords fullerenoimidazopyrimidines, whose electron affinity is higher than that of nonmodified C₆₀.     

Synthesis of new fluorine-containing derivatives of quinoxaline 1,4-dioxides and condensed systems derived from them

The Beirut reaction of 5,6-difluorobenzofuroxan with 1,3-diketones, β-ketoesters, and amides produces 6,7-difluoroquinoxaline 1,4-dioxides. The condensation of 2-ethoxycarbonyl-6,7-difluoro-3-methylquinoxaline 1,4-dioxide is studied. Fluorinated furo[3,4-b]- and pyrrolo[3,4-b]quinoxaline 4,9-dioxides are synthesized and further functionalized by nucleophilic substitution of fluorine and reduction of the N-O bond. Dedicated to Professor Henk van der Plas on his 70th birthday. Ural's State Technical University, Ekaterinburg 62002, Russia; e-mail: azine@htf.rcupi.e-burg.su. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 520–531, April, 1999.     

Transformations of C-adducts of 1,4-diazinium salts with dicarbonyl compounds into polycyclic systems

C-Adducts of 5-(het)aryl-2,3-dicyano-1-pyrazinium salts containing a residue of a 1,3-dicarbonyl compound at position 6 can be involved in the cyclization with hydrazine hydrate giving rise to pyrazino[2,3-c]pyridazines along with the expected pyrazole derivatives. The reactions of the same σ^H-adducts with hydroxylamine unexpectedly afforded triazacyclopenta[a]indene derivatives. The crystallographic data on the three-dimensional structures of new polycyclic compounds were obtained. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 639–643, March, 2008.     

Mechanism of nucleophilic substitution of hydrogen in azines IV. Role of one-electron transfer in reactions with arylamines

A satisfactory correlation between the polarographic reduction potentials and the calculated energies of the lower vacant molecular orbitals was found for a number of N-methylazinium cations. The result of the aza effect and the benzoannelation effect is a shift of the reduction potentials to the positive region by 0.2–0.5 and 0.2–0.7 V, respectively. Electron transfer from N,N,N,N-tetramethyl-p-phenylenediamine to the most electrophilic cations was recorded. The possibility of the occurrence of reactions involving aminoarylation of the acridinium cation via a one-electron mechanism was demonstrated electrochemically and by model reactions.See [1] for communication III.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 690–694, May, 1977.