Corannulene, extended

D. Corannulene with Extended jr-Systems—From Bowls to Balls. 501... 

Highly substituted corannulenes are not only important building blocks for new organic materials, they also provide the possibility to extend the aromatic system of the corannulene core. Direct multiple electrophilic aromatic substitution oti corannulene has shown limited but important successes. In contrast, functiOTial-ization of multihalocorannulenes is a general route. 

Rabinovitz and co-workers also used the Haworth phenanthrene synthesis to form complex fused aromatic ring systems." The bowl-like shape of corannulene 57 was extended through the acylation reaction with 58 to produce 59. Treatment of 59 with red phosphorus under strongly acidic conditions resulted in 60 in good yield. 

The PAHs indenocorannulene (39), dibenzo[a,g]corannulene (40), and diben-zo[o,g]cyclopenta[h,I]corannulene (41) are three examples of extended corannulenes, which contain a central corannulene system fused to five- and six-membered rings. The reduction of these systems [119, 120] focused on the following issues. First, what is the aromaticity of these curved PAHs anions, will they behave like large polycyclic systems, or have aimulenic character Secondly, what is the possibility of aggregation and dimerization in these systems The third subject of interest was the effect of different alkali metals on the reduction process. 

The 4/2+2 rule solved the mystery of the profound difference between benzene, [10]annulene, [14]-annulene, and [ISjannulene on one side and the 4/2 monocyclic systems, like elusive cyclobutadiene and puckered cyclooctatetraene, on the other side. Attempts were made to extend the 4/2+2 rule to polycyclic systems, for which it was not initially designed. Of numerous attempts in this direction, we will mention only that of Platt,who proposed that the 4/2+2 rule be applied to molecular periphery. It turns out that Platt s generalization of the Hiickel 4/2+2 rule is correct when one restricts attention to benzenoid hydrocarbons. For example, the perimeter rule correctly classifies pyrene (which has 16 Jt-elec-trons), perylene (which has 20 //-electrons), and coronene (which has 24 //-electrons) as aromatic as they have 14 or 18 //-electrons on the perimeter. But the perimeter rule does not give a correct answer for the non-benzenoid systems illustrated in Figure 10. The structure on the left, which has 14 //-electrons on the periphery, instead of being aromatic, as will be seen later, is in fact fully anti-aromatic . On the other hand, the structure on the right (corannulene), which has 15 //-electrons on the periphery, is not... 

---