Two new, more convenient methods for the synthesis of 1,2,4-triazol-5-ylidenes are described. Four new 1,2,4-triazol-5-ylidenes have been prepared using these methods: 1-(1-adamantyl)-3,4-diphenyl-1,2,4-triazol-5-ylidene (2a), 1-(1-adamantyl)-3-phenyl-4-(p-bromophenyl)-1,2,4-triazol-5-ylidene (2b), 1-(1-adamantyl)-3-phenyl-4-(alpha-naphthyl)-1,2,4-triazol-5-ylidene (2c), and 1-(1-adamantyl)-3,4-di(p-bromophenyl)-1,2,4-triazol-5-ylidene (2d). The X-ray crystal structures of 2d and the precursor salt 1-(1-adamantyl)-3,4-di(p-bromophenyl)-1,2,4-triazolium bromide (1e) are described. Compound 2a reacts with CH(3)CN via C-H insertion to form 1-(1-adamantyl)-3,4-diphenyl-5-cyanomethyl-5H-1,2,4-triazoline (3), and 2a and 2d react with elemental sulfur and elemental selenium, respectively, to form the corresponding thione (4) and selenone (5).

Organic chemistry Z 0200Stable Heteroaromatic Carbenes of the Benzimidazole and 1,2,4-Triazole Series -[109 refs.]. -(KOROTKIKH, N. I.; SHVAIKA, O. P.; RAYENKO, G. F.; KISELYOV, A. V.; KNISHEVITSKY, A. V.; COWLEY, A. H.; JONES, J. N.; MACDONALD, C. L. B.; ARKIVOC (Gainesville, FL, US) 2005, 8, 10-43; Litvinenko Inst. Phys. Org. Chem., Natl. Acad. Sci. Ukr., Donetsk 340114, Ukraine; Eng.) -Lindner 02-258

Four stable carbenes, 1-tert-butyl-3,4-diaryl-1,2,4-triazol-5-ylidenes 1a-d, including new fluorine-containing compounds 1c,d, react with a malonic ester to afford heterocyclic zwitterionic compounds 5a-d. The reactions with more acidic compounds (ethyl acetoacetate, malononitrile and 1,3-dimethylbarbituric acid) proceed with substrate deprotonation to form the respective azolium salts 6a-c. The X-ray crystal structure of 5a was also determined.

The fundamental researches in the chemistry of stable carbenes carried out by the L.M. Litvinenko Institute of Physical, Organic & Coal Chemistry of the NAS of Ukraine (IPOCC) over the last decade and applications in the field of «green» technologies based on the results of these researches have been described. Carbene versions of Claisen ester condensation with the formation of zwitterionic compounds, the Leuckart-Wallach reaction with the autoreduction of carbenoid azolium salts, the Hofmann cleavage of aminocarbene insertion products, induced tandem autotransformation of 1,2,4-triazol-5-ylidenes into 5-amidino-1,2,4-triazoles have been discovered. New carbene reactions of addition, deesterification, oxidation, and complex formation have been found. Effective methods for obtaining stable carbenes and carbenoids have been suggested. New types of carbenes, benzimidazolylidenes, superstable conjugated bis-carbenes, and carbenoids have been synthesized. The existence of hypernucleophilic carbenes has been theoretically predicted and experimentally confirmed. Prospects for the use of carbenes and their derivatives, in particular, carbene complexes of transition metals in the catalysis of organic reactions and the search of biologically active compounds have been outlined. K e y w o r d s: heteroaromatic carbenes, synthesis, properties, transformations, catalysis, biological activity, and «green» chemistry.

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