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Previously unknown heterocyclic carbenes and their precursors containing a silicon atom in the side chain were prepared. Their structures were studied by multinuclear 1H, 13C, 15N, and 29Si NMR spectroscopy.

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.

2-Benzoylmethylene-1,3,5-dithiazinium hydrobromides were prepared in high yield by the reaction of 1-bromo-2-benzoylacetylene with 2,4-dithiobiurete and its mono- and disubstituted derivatives in glacial AcOH. The ability of the compounds synthesized to undergo further chemical transformations has been studied.

[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.

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.

The obtained correlation between the 35Cl NQR frequencies for organic and the corresponding organometallic compounds CIMXX′X″ (M=C, Si, Ge, Sn) shows that transmission of the electronic effects of substituents across the M atom increases in the following order: Si

The 35 Cl NQR spectra show that the adducts of tertiary amides R 2 NCOR' (R = CH 3 , C 2 H 5 ; R' = H, C 6 H 5 ) and phosphorus halides PCl 5 and POCl 3 have the structure: At the same time the reaction of (CH 3 )C 6 H 5 NCOCH 3 or (C 6 H 5 ) 2 NCOCH 3 with PCl 5 leads to organylchlorophosphonylhexachlorophosphate [RR'NCCl = CHPCl 3 ] + · PCl 6 − . The NQR spectrum of the adduct of DMF with PCl 3 does not agree with that suggested previously from IR- and PMR- spectra.

Asymmetry parameters for the electric field gradient at the 35Cl nuclei of polycrystalline Cl(CH2)3SnCl3 have been measured at 77 K. They are in agreement with a trigonal-bipyramidal structure for the molecule. The electron distribution of the axial chlorine atom in the SnCl3 group is almost axially symmetric whereas that of the two equatorial atoms and the chlorine atom in the Cl(CH2)3 group deviate noticeably from the axial symmetry. The deviation is mainly due to the interaction of the lone electron pair of the corresponding chlorine atom with the central tin atom.

N-Mono-alkylated imidazoles and benzimidazoles were prepared both by the traditional method and by microwave-assisted reaction. Their dialkylated salts were obtained, which are precursors for carbenes and novel 1,3-dialkylated imidazol-2-ilidenes and -benzimidazol-2-ilidenes.

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.