A Crowning Achievement: The First Solution-Phase Synthesis of Circumcoronenes

Circumcoronene is a highly symmetric polybenzenoid hydrocarbon that has fascinated organic chemists and materials scientists for decades. However, until recently, it had only been studied theoretically, because its synthesis in solution remained challenging. In a recent report, Wu and co-workers described the first successful solution-phase synthesis and isolation of crystalline circumcoronene derivatives, validating the long-predicted Clar structure. Their synthetic approach enables preparation of new polycyclic benzenoid hydrocarbons with multiple K-regions, which are difficult to obtain, and expands our understanding of the chemistry of these systems.     

Circumcoronenes

Circumcoronene, a hexagonal graphene fragment with six zigzag edges, has been the focus of theoretical studies for many years, but its synthesis in solution has remained a challenge. In this study, we present a facile method for synthesizing three derivatives of circumcoronene using Brønsted/Lewis acid-mediated cyclization of vinyl ether or alkyne. Their structures were confirmed through X-ray crystallographic analysis. Bond length analysis, NMR measurement, and theoretical calculations showed that circumcoronene mostly follows Clar's bonding model and exhibits dominant local aromaticity. Its absorption and emission spectra are similar to those of the smaller hexagonal coronene due to its six-fold symmetry.