Nomenclature ylidene

Concerning nomenclature, fulvalene 2 and its related systems 1 and 3-6 are the parent structures of this class of heterocyclic cross-conjugated compounds. Both ring systems are numbered as shown in formula 9 (1,4,5,8-tetraazafulva-lene) beginning at the heteroatoms. Alternatively, as in the case of heptafulva-lene 10 (3,3 -diazaheptafulvalene), the numbers 1-7 and l -7 can be used.Tlie use of the name of the parent heterocycle connected by an olefinic double bond is often favored for the nomenclature of electron-rich olefines, for example, bis[3-(2,6-diisopropylphenyl)-4,5-dimethylthiazol-2-ylidene] for compound 51a (97LAR365). Similarly, azafulvalenes of type 11 and 12 can be re-... 

Note 2. The use of prefixes ending in -ylidene for gem-bivalent substituent groups is traditional in the carbohydrate field, although no longer recommended in general organic nomenclature [14],... 

Other structures such as a-(l,2-dithiol-3-ylidene)ketones (12) can be named according to common nomenclature because they do not possess the symmetry of the l,6,6a Slv-trithiapentalenes. However, even with such unsymmetrical systems, pentalene names may be useful, either to stress the fact that three heteroatoms are in line or to show the similarity with trithiapentalene derivatives, for instance, in the case of selenium analogs (13). 

These compounds are usually called l-alkynyl)carbene complexes or 2-alkyn-l-ylidene complexes, but the nomenclature l-metalla-alk-l-en-3-ynes has been used see Refs. 48 and 122, and Aumann, R. Heinen, H. Chem. Ber. 1987, 120, 537... 

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