Angular fusion

Polynuclear aromatic hydrocarbons formed by the angular fusion of benzene rings may adopt either planar or nOnplanar minimum energy conformations, as demonstrated by the circulenes 8-10. [6]Circulene (coronene 9), the earliest known member of the family, prefers a planar structure of symmetry since the presence... 

The possibility of regioselective angular fusion has been demonstrated in the annelation of two benzo[ ][l,8]naphthyridine units on to a 1,8-naphthyridine nucleus, leading to three isomeric octacyclic compounds (79JOC531). The condensation between two molecules of 2-aminonicotinaldehyde, two of cyclohexane-1,3-dione and one of 4-aminopyrimidine-5-carbaldehyde gave a mixture of the three isomeric products (420), (421) and (422). 

The 13C shifts of the other hydroaromates (Table 4.57) are closely related to those of tetralin. Angular fusion of the rings usually causes a slight sterically induced shielding of the o, o or a, a carbons, as can be seen for the hydrogenated phenanthrene derivatives. 

Distributions of pyrolytic PAFls are characterized by the dominance of the non-alkylated species shown in Fig. 7.3. Particularly abundant are the highly peri-condensed compounds—such as pyrene, the benzopyrenes, benzo[gfe]perylene and coronene—that result from extensive angular fusion of benzenoid systems.The presence of such PAF1 distributions in the aromatic... 

Peri fusion Angular fusion of benzenes, as in the three-ring system phcmin-Ihrcne. 

Naphthalene, anthracene, and phenanthrene are the three simplest members of this class. They are all present in coal tar, a mixture of organic substances formed by heating coal at about 1000°C in the absence of air. Naphthalene is bicyclic and its two benzene rings share a common side. Anthracene and phenanthrene are both tricyclic aromatic hydrocarbons. Anthracene has three rings fused in a linear fashion an angular fusion characterizes phenanthrene. The structural formulas of naphthalene, anthracene, and phenanthrene are shown along with the numbering system used to name their substituted derivatives ... 

Angular s. Annelation, angular, Fusion, -, Methyl groups, -, Substitution, -... 

Continued angular fusion of benzene rings to phenanthrene eventually results in helical polycyclic benzenoid arrays, called helicenes. These molecules are chiral and, when they are optically pure, exhibit extraordinary specific rotations—for example, for the helicene shown,... 

For the preparation of 71 (Scheme 4.17), a strategy was necessary that desymme-trized the sixfold symmetry of 20 to allow for the generation of angular fusion. It started with trialdehyde 67 [78], which was coupled with TMSA in 97% yield, to... 

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