Facile synthesis of aryl-substituted cycloarenes via bismuth(III) triflate-catalyzed cyclization of vinyl ethers

Cycloarenes are an essential class of polycyclic aromatic hydrocarbons with unique electronic structure, but their synthesis is very challenging. Herein, we report a facile synthetic strategy primarily involving macrocyclization by the Suzuki coupling reaction, followed by bismuth(III) triflate-catalyzed cyclization of vinyl ethers. By utilizing this approach, aryl-substituted soluble cycloarenes 7 and 8 with different sizes were obtained. X-ray crystallographic analysis revealed a slightly distorted backbone in the kekulene derivative 7 and a saddle-shaped skeleton in the octulene derivative 8. Bond length analysis suggested that both of the cycloarenes mainly complied with the Clar's bonding model with dominant local aromaticity, which was also in accord with our NMR measurements and the theoretical calculations [nucleus-independent chemical shift [NICS], anisotropy of the induced current density (ACID), three-dimensional isochemical shielding surface (3D ICSS)]. The optical properties were investigated by UV-Vis absorption and fluorescence spectral measurements. Our method opens opportunities to access various expanded and core-modified cycloarenes in the future.