Enantioselective synthesis of a chiral nitrogen-doped buckybowl.

Bowl-shaped aromatic compounds, namely buckybowls constitute a family of curved polycyclic aromatic carbons along with fullerenes and carbon nanotubes. Doping of heteroatoms to the carbon frameworks of such aromatic compounds drastically modulates their physical and chemical properties. In contrast to nitrogen-doped azafullerenes or carbon nanotubes, synthesis of azabuckybowls, nitrogen-doped buckybowls, remains an unsolved challenging task. Here we report the first enantioselective synthesis of a chiral azabuckybowl, triazasumanene. X-ray crystallographic analysis confirmed that the doping of nitrogen induces a more curved and deeper bowl structure than in all-carbon buckybowls. As a result of the deeper bowl structure, the activation energy for the bowl inversion (thermal flipping of the bowl structure) reaches an extraordinarily high value (42.2 kcal per mol). As the bowl inversion corresponds to the racemization process for chiral buckybowls, this high bowl inversion energy leads to very stable chirality of triazasumanene.