A Missing Link between Classic Flat Aromatics and Novel Fullerenes

Circumtrindene (C₃₆H₁₂), one of the largest members of open geodesic polyarenes, exhibits fullerene-like reactivity at the interior carbon atoms, while it still possesses aromatic reactivity at the edge carbons. Among various chemical modification methods for such polyarenes, covalent functionalization plays an important role in altering their chemical and physical properties as demonstrated in the chemistry of fullerenes, carbon nanotubes, and their fragments. Herein, we report synthetic methods to functionalize a fullerene fragment, circumtrindene, via site-selective covalent bond formation. The Bingel–Hirsch and Prato reactions (traditional methods for fullerene functionalization) of circumtrindene afforded circumtrindene derivatives with one of the interior C–C bonds modified. These reactions represent the first examples of functionalization at interior carbon atoms of a non-fullerene polycyclic aromatic hydrocarbon (PAH). On the other hand, one of the most common classes of aromatic reactions, electrophilic substitution, led to the functionalization on the rim of circumtrindene. This peripheral functionalization was utilized to extend the π system of the polyarene with subsequent coupling reactions and to explore the magnetic environment of the compound. For both classes of functionalization, theoretical investigations are conducted to support the experimental results.