B. I. Buzykin

Tautomerism of aza cycles: II. Synthesis and structure of 5-substituted 3-(2-hydroxyethylsulfanyl)-1H-1,2,4-triazoles and their salts. Preference of the 1H,4H-1,2,4-triazolium tautomers

New complexing agents, potentially tautomeric 3-(2-hydroxyethylsulfanyl)-1H-1,2,4-triazole, its 5-methyl-and 5-phenyl-substituted analogs, and some their salts, were synthesized, and their structure was discussed on the basis of the 1H and 13C NMR, IR, and mass spectra, X-ray diffraction data, and published data. In keeping with the rule formulated previously for N-unsubstituted 1,2,4-triazoles having dissimilar substituents, the synthesized compounds were found to exist as 3-(2-hydroxyethylsulfanyl)-5-R-1H-1,2,4-triazole tautomers (3-RA-5-RD-1H-1,2,4-triazoly). They are protonated at the nitrogen atom in position 4 of the triazole ring. The 1H and 13C NMR spectra of these compounds in trifluoroacetic acid suggest the presence of two forms due to equilibrium between the neutral and protonated species. Analysis of the crystallographic data for the triazolium salts and published data showed preference of the 1H,4H-1,2,4-triazolium tautomer.

Tautomerism of aza cycles: I. Structure of 3(5)-butylsulfanyl-5(3)-methyl(phenyl)-1H-1,2,4-triazole tautomers in crystal. Preference of the 3-RA-5-RD-1H-tautomer of 3(5)-mono-and 3,5-disubstituted 1,2,4-triazoles

The X-ray diffraction study of potentially tautomeric 3(5)-butylsulfanyl-5(3)-methyl-1H-1,2,4-triazole and its 5(3)-phenyl-substituted analog showed that these compounds in crystal have the structure of 3-butylsulfanyl-5-methyl(phenyl)-1H-tautomers. Analysis of our experimental and published data indicated that 3(5)-monosubstituted 1,2,4-triazoles and 3,5-disubstituted derivatives having nonequivalent substituents in crystal as exist as a tautomer in which the electron-acceptor substituent (RA) occupies the 3 position, while the electron-donor substituent (RD) resides in the 5 position, i.e., as 3-RA-5-RD-1H-1,2,4-triazoles. Symmetric 3,5-disubstituted 1,2,4-triazoles could give rise to tautomeric equilibrium between the 1H-and 2H-structures even in crystal.

Electron spin and electron nuclear double resonances of the stable 1-(4-nitrophenyl)-3-phenyl-1,4-dihydro-1,2,4-benzotriazin-4-yl free radical

The 1H and 14N hyperfine structure constants for the stable 1-(4-nitrophenyl)-3-phenyl-1,4-dihydro-1,2,4-benzotriazin-4-yl free radical obtained by the oxidation of 1-(4-nitrophenyl)-3-phenyl-1,4-dihydro-1,2,4-benzotriazine or N-phenylbenzamide 4-nitrophenylhydrazone were determined by the ESR and 1H electron nuclear double resonance methods.

2-chloro-3,3,5-trimethyl-2,3-dihydro-1,2λ5-oxaphosphole 2-oxide as precursor in a new synthesis of dialkyl(diaryl)-(2-methyl-4-oxopent-2-yl)phosphine oxides

A new approach has been developed to the synthesis of dialkyl(diaryl)(2-methyl-4-oxopent-2-yl)-phosphine oxides that are structural analogs of the drug dimephosphon. This approach is based on the reaction of 2-chloro-3,3,5-trimethyl-3H-1,2λ5-oxaphosphole 2-oxide with Grignard compounds, and it ensures high yields of the target products. The structure of bis(2-methoxyphenyl)(2-methyl-4-oxopent-2-yl)phosphine oxide was determined by X-ray analysis. (2-Methyl-4-oxopent-2-yl)dipropylphosphine oxide with magnesium bromide formed a 4: 1 complex whose structure was also determined by X-ray analysis.

Tautomerism of azacycles: III. Molecular and crystal structures of 3H-and 2-phenyl-1H,4H-4,5-dihydro-1,2,4-triazole-5-thiones

Compounds capable of tautomerism: sulfanyl-1,2,4-triazole, its C-phenyl derivative, and the crystal hydrate of the latter, were studied by single crystal X-ray diffraction. In the crystals they exist in the form of 3-R-1(H),4(H)-4,5-dihydro-1,2,4-triazole-5-thione with a considerable contribution of the bipolar structure. Published data on the tautomerism of sulfanyl-1,2,4-triazoles and their N-substituted analogs and on the correlation between the spectral characteristics and structures of sulfanyl-1,2,4-triazoles capable of tautomerism are discussed.

Dimephosphone analogs: a pharmacological aspect

We studied some pharmacological properties of dimephosphone P—C and aza analogs, viz., dimethyl (2-methyl-4-oxopent-2-yl)phosphonate, which is one of the first organophosphorus drugs having no anticholinesterase activity. Replacement of two P—O—C fragments in dialkyl (2-methyl-4-oxopent-2-yl)phosphonates with the P—C ones on going to dialkyl-(2-methyl-4-oxopent-2-yl)phosphine oxides results in a dramatic decrease in the acute toxicity of the latter to warmblooded animals. The toxicities of dimephosphone aza analogs and (γ-oxoalkyl)phosphine oxides under study depend on the nature of aza fragment introduced instead of the oxygen atom. Dimephosphone pyridinoylhydrazones were found to exhibit a high antiinflammatory activity, which increases the interest for this type compounds as promising tuberculostatics.

Pfitzinger reaction of dialkyl(aryl)(2-methyl-4-oxopent-2-yl)phosphine oxides

New phosphorus-containing derivatives of quinoline-4-carboxylic acid were synthesized by the Pfitzinger reaction from isatin and dialkyl(aryl)(2-methyl-4-oxopent-2-yl)phosphine oxides.

Dimephosphone analogs: II. Dialkyl(diaryl)-(2-methyl-4-oxopent-2-yl)phosphine oxide oximes: Synthesis, structure, and generation of iminoxyl radicals

Dialkyl(diaryl)-(2-methyl-4-oxopent-2-yl)phosphine oxide oximes have been synthesized for the first time. According to the X-ray diffraction data, these compounds in crystal exist as a single E isomer. Their structure in solution and the E/Z isomer ratio were determined by 1H and 13C NMR spectroscopy.

Unusual structure and reactions of 1-phenlpyrazol-5-one annulated with 1-methylpiperidine. A rare case of auto-alkylation

The interaction of 1-alkyl-3-alkoxycarbonylpyperidin-4-ones with phenylhydrazine has led to 5-alkyl-2-phenyl-3,3a,4,5,6,7-hexahydro-2H-pyrazolo-[4,3-c]pyridin-3-ones. The prepared compounds are unstable and undergo a series of uncommon transformations; their mechanisms have been suggested basing on the structural analysis of the product mixtures.

Dimephosphone Analogs: I. Synthesis and Structure of Some Dimephosphone Aryl- and Acylhydrazones

Dimephosphone (2-dimethoxyphosphoryl-2-methylpentan-4-one) phenyl-, nitrophenyl-, benzoyl-, and 4-nitrobenzoylhydrazones were synthesized. The compounds in crystals were shown to have a steric form exclusively of the E-isomer. The structure of hydrazones in solution is defined by the nature of the substituents and the solvent and the time of storage of the solution. The dimephosphone aroylhydrazones in acid solutions exist in several possible forms: the isomers at the imine bond, the conformers at the amide bond, and a cyclic tautomer (1,3,4-oxadiazoline).