Fluorinated and trifluoromethylated corannulenes

The syntheses and properties of corannulenes carrying electron-withdrawing groups (F, CF₃, C₆F₅) are reported. Direct fluorination of corannulene (C₂₀H₁₀) was carried out with xenon difluoride, and the crystal structure of the product was confirmed by the X-ray analysis. Novel trifluoromethylated corannulenes, including the versatile 4,9-dibromo-1,2-bis(trifluoromethyl)corannulene, were obtained by various established ring-closing reactions. Besides the use of hexafluorobutyne for the construction of fluoranthenes by Diels-Alder reaction as precursor molecules to form 1,2-disubstituted corannulenes, bis(pentafluorophenyl)acetylene was employed as dienophile. The molecular structure and crystal packing of a trifluoromethylated corannulene was determined by single-crystal X-ray analysis and compared with those known brominated and trifluoromethylated corannulenes. The general electron-acceptor properties of corannulenes bearing substituents introduced in particular positions by liquid-phase synthesis are discussed together with published computational results. Stacked bowls: Starting from substituted fluoranthenes, novel corannulenes bearing electron-withdrawing groups were synthesized regioselectively. Moreover, the first fluorinated corannulene was synthesized by direct fluorination. Crystallographically studied trifluoromethylated corannulenes showed desirable π-stacked structures (see figure), despite their electron-acceptor strength in solution.