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.

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A series of new stable halogenated carbenes, 1-tert-butyl-3,4-diaryl-1,2,4-triazol-5-ylidenes, has been synthesized.

The review is focused on new data concerning the syntheses and selected properties of stable heteroaromatic monocarbenes of the benzimidazole and 1,2,4-triazole series, biscarbenes, anionocarbenes of the 1,2,4-triazole series, and cryptocarbenes. The syntheses of the precursors to these compounds are also described. Special attention is paid to C-H insertion reactions, X-ray structural data and spectral characteristics of the carbenes and their analogues.

Review: 70 refs.