Fused Dibenzo[a,m]rubicene: A New Bowl-Shaped Subunit of C70 Containing Two Pentagons

Total synthetic approaches of fullerenes are the holy grail for organic chemistry. So far, the main attempts have focused on the synthesis of the buckmin-sterfullerene C-60. In contrast, access to subunits of the homologue C-70 remains challenging. Here, we demonstrate an efficient bottom-up strategy toward a novel bowl-shaped polycyclic aromatic hydrocarbons (PAH) C34 with two pentagons. This PAH represents a subunit for C-70 and of other higher fullerenes. The bowl-shaped structure was unambiguously determined by X-ray crystallography. A bowl-to-bowl inversion for a C-70 fragment in solution was investigated by dynamic NMR analysis, showing a bowl-to-bowl inversion energy (Delta G double dagger) of 16.7 kcal mol(-1), which is further corroborated by DFT calculations.