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Novel 2-acetylamino-4-acetyl-5-aryl(heteryl)-1,3,4-thiadiazolines, 2-acetylamino-5-aryl(heteryl)-1,3,4-thiadiazoles, and some of their salts were prepared and studied by multinuclear 1H, 13C, 15N, 19F and 2D NMR spectroscopy. The acetylation of thiosemicarbazones is accompanied by ring closure to form the corresponding 1,3,4-thiadiazolines and 1,3,4-thiadiazoles. 15N NMR spectroscopy is a unique method for the identification of thiadiazole pyridinium salts. Copyright © 2007 John Wiley & Sons, Ltd.

The vicarious nucleophilic substitution of hydrogen in symmetrical and vicinal nitrotriazoles by 1,1,1-trimethylhydrazinium iodide in t-BuOK/DMSO was studied by ESR. In the ESR monitoring of the reactions the primary radical-anions of 4-nitro-2-phenyl-1,2,3-triazole and 1-methyl-3-nitro-1,2,4-triazole were detected and characterized. It was shown by NMR that the amination of 4-nitro-2-phenyl-1,2,3-triazole takes place exclusively in the triazole ring with the formation of 5-amino-4-nitro-2-phenyl-1,2,3-triazole. 1-Methyl-3-nitro-1,2,4-triazole, like 3-nitro-1,2,4-triazole, does not form amination products. A possible mechanism for the vicarious C-amination of nitrotriazoles and the formation of the radical-anions of the substrates is discussed.

A potential surface of rotational transformations of 1,3-di(silylmethyl)imidazol-2-ylidene and its halo-substituted analogs has been analyzed using quantum-chemical methods. Coordination interactions of the carbene center with Si-fragments have been studied. It is shown that the above interaction results in a structural reorganization of the silicon centers from the tetrahedral state to the trigonal–bipyramidal. This leads to a considerable stabilization of compounds in the planar state. The stabilization effect is strengthened by halogenation.

[4-Phenyl-2H-1,3-thiazin]-2-ylideneguanidinium perchlorate or acetoxytrifluoroborate respectively was obtained from the reaction of benzoylacetylene with N-amidinothiourea in glacial AcOH in the presence of an equimolar quantity of HClO4 or BF3⋅Et2O. These compounds underwent hydrolysis at the amidine unit on treatment with acid or base. For example, the perchlorate on heating in HClO4 was converted into 2-imino-4-phenyl-2H-1,3-thiazinium perchlorate, while treatment with aqueous NaOH in DMSO gave the free base - 6-phenyl-1,2-dihydropyrimidine-2-thione.

A number of N-alkylimidazoles and N-alkylbenzimidazoles were synthesized by reactions of imidazole and benzimidazole with alkyl halides. The reaction rate increases by a factor of 2 to 3 under conditions of microwave activation. Subsequent treatment of the resulting N-alkylazoles with alkyl halides afforded the corresponding 1,3-dialkylimidazolium and 1,3-dialkylbenzimidazolium halides.

The nucleophilic addition of 2,4-dithiobiurete, 1- and 1,4-substituted 2,4-dithiobiuretes (2 a-e) with benzoylacetylene (1) has been studied. 2-(Benzoylmethyl)-4-(R1-imino)-6-(R2-imino)dihydro-4H-1,3,5-dithiazinium perchlorates (3 a-e) are obtained in glacial acetic acid (AcOH) in the presence of equimolar quantities of HClO4. The reaction of benzoylacetylene with 1,5-diphenyl-2,4-dithiobiurete in either of MeOH, C6H6, or MeCN solvents proceeds non-selectively to give a mixture of products such as 2-(benzoylmethyl)-4,6-di(phenylimino)dihydro-4H-1,3,5-dithiazine (5), 2-(benzoylmethyl)-4-(β-benzoylvinyl)thio-3-phenyl-6-(phenylimino)-3,6-dihydro-2H-1,3,5-thiadiazine (8), 2-(benzoylmethyl)-1,3-diphenylhexahydro-1,3,5-triazine-4,6-dithione (7) and N-(β-benzoylvinyl)-N-phenylthioureas (6).

The correlation between the group dipole moments of substituents and the experimental values of ionization potentials has demonstarted that the position of the lower ionic π state of allylamine, allylmercaptane, allyl alcohol, and other organic allyl derivatives (except allyl bromide) was determined by the field effect. The empirically obtained conclusions were confirmed by semiempirical AM1 studies. The mechanism of destabilization of energetically unfavorable rotational isomers in the above series of compounds was considered, and it was found that this destabilization is caused mainly by electrostatic interaction.

The 35Cl NQR spectra of 3,5-dichloro-1,2,4-triazole derivatives have been examined. MNDO calculations of chloroazoles (imidazole, triazole) including their ionic forms have been carried out. In 3,5-dichloro-l,2,4-triazole complexation and protonation occur of position 4 at the triazole ring.

Vicarious nucleophilic C-amination of nitrobenzene, 1-methyl-5-nitrobenzimidazole, and 1-methyl-6-nitrobenzimidazole in superbasic medium (potassium tert-butoxide-dimethyl sulfoxide) gave the corresponding amino-substituted derivatives. The yield of the amination product of 1-methyl-5-nitrobenzimidazole considerably increased in the presence of CuCl. ESR monitoring of these reactions revealed formation of primary radical anions from the substrates. Possible reaction mechanisms are discussed.

Silylotropy in 4-substitutedN-trimethylsilypyrazoles is studied by dynamic1H,13C, and29Si NMR spectroscopy. The catalytic 1,2-migration of a trimethylsilyl group in 4-halo-N-trimethylsilylpyrazoles was detected. Silylotropy inN-trimethylsilylpyrazoles in the presence of halogens of trimethylhalosilanes is believed to proceed through formation ofN,N′-bis(trimethylsilyl)pyrazolium salts, the barrier of silylotropy in pyrazoles being markedly reduced.

Asymmetry parameters of the electric field gradients at the 35Cl nuclei in compounds of the RC6H4COCl series (R = H, 4-CH3, 2-, 3- and 4-COCl) have been measured at 77 K. They indicate a high asymmetry (> 20%) of the chlorine electron distribution in all the molecules studied. The substituent R in the aromatic ring has no significant effect on the asymmetry.

The condensation of PhCH2Cl with the liberation of HCl catalyzed by SnCl4, occurs in the PhCH2Cl-SnCl4. system. The proposal of the existence of a cis-octahedral complex, 2PhCH2Cl· SnCl4, was proved erroneous.