Thiopyrylium Scaffolds from the Lewis/Brønsted-Acid-Promoted Cyclization of Thioethers

A series of acene- or heteroacene-fused thiopyrylium salts was synthesized from diarylthioethers that contain formyl groups via an intramolecular Friedel-Crafts cyclization. The reaction, promoted by a Lewis or Brønsted acid, afforded the new thiopyrylium salts in good yield. Kinetic investigations and density functional theory calculations were used to explore the mechanism of the reaction. The electronic structures of the thiopyrylium salts were examined by UV-vis absorption spectroscopy, which afforded insight into the electronic transitions within these molecules.