Expanded Kekulenes

The synthesis of kekulene and its higher homologues is a challenging task in organic chemistry. The first successful synthesis and characterization of the parent kekulene were reported by Diederich and Staab in 1978. Herein, we report the facile preparation of a series of edge-extended kekulenes by bismuth(III) triflate-catalyzed cyclization of vinyl ethers from the properly designed macrocyclic precursors. Their molecular structures were confirmed by X-ray crystallographic analysis and NMR spectroscopy. Their size- and symmetry-dependent electronic structures (frontier molecular orbitals, aromaticity) and physical properties (optical and electrochemical) were investigated by various spectroscopic measurements, assisted by theoretical calculations. Particularly, the acene-like units along each zigzag edge demonstrate a dominant local aromatic character. Our studies provide an easy synthetic strategy toward various fully fused carbon nanostructures and give some insights into the electronic properties of cycloarenes.