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

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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.

The first tandem autotransformations of heteroaromatic carbenes have been found. These reactions involve cleavage of the 1-tert-butyl-3,4-diaryl-1,2,4-triazol-5-ylidenes 1a-d to form benzonitriles and the respective carbodiimides, followed by further reactions of the latter with carbenes 1a-d to afford the 3,4-diaryl-5-(1-tert-butyl-3-arylamidin-2-yl)-1,2,4-triazoles 5a-d. The X-ray structures of the carbene 1-tert-butyl-3-phenyl-4-n-bromophenyl-1,2,4-triazol-5-ylidene (1a) and the amidinotriazole 3-phenyl-4-p-bromophenyl-5-(1-tert-butyl-3-pbromophenylamidin-2-yl)-1,2,4-triazole (5a) were determined. The reactions of 1a with the electrophiles diphenylcarbodiimide, acetonitrile, and diphenyldiazomethane are also described.