Fulvenes, tria

Fulvenes are cyclic, cross-conjugated molecules with an odd number of carbon atoms in the ring. According to the size of the ring skeleton they are named tria- (A), penta- (B), hepta- (C), and nonafulvenes (D) (Fig. 1) [6]. 

Consider the case of triapentafulvalene (XIV) (calicene), a combination of tria-fulvene and pentafulvene. Hexaphenyltriapentafulvalene (XV) [37] was taken as a representative. This compound has the highest experimental dipole moment in the ground state ever recorded in a hydrocarbon - 6.3D (benzene, 30°C) [37]. A similar value was obtained in the case of the l,2-dimenthyl-3,4,5,6-tetraphenyl derivative [38]. 

Similar to the reaction sequence shown in Scheme 4.2, l,2-bis(3,5-di-terl-butyl-4-hydroxyphenyl)cyclopropenone (16) was converted into [3]radialenes 18 by a Knoevenagel-type condensation followed by oxidation of the tria-fulvene intermediates 17 (Scheme 4.3) [16]. Other similar compounds, such as the 2-(dicyanomethylene)-substituted 2,5-thienoquino-, 2,5-selenoquino-,... 

In addition, the same group reported on a synthesis of heptafulvenes and related seven-membered ring systems (e.g., 363) from triafulvene 357 (Scheme 7.80) [91]. A series of donor-substituted 1,3-dienes, when reacted with tria-fulvenes by a Diels-Alder addition, yielded bicyclic methylene cyclopropanes, which were subsequently transformed to 1,6-diphenyl-substituted heptafulvenes or seven-membered ring derivatives. 

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See also in sourсe #XX -- [ ]

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