Pyrano[3,4-c]pyrandiium dication

Pyrano[3,4-c]pyrandiium dication has been detected in anhydrous D₂SO₄ using two-dimensional correlation NMR spectroscopy. The dication is generated as an intermediate in acid-catalyzed hydrolysis of 1-ethoxy-5-methyl-3,8-diphenyl-1H-pyrano[3,4-c]pyran-7-ium perchlorate, where the action of 70% HClO₄ leads to the replacement of ethoxy group by hydroxyl one, and the reaction with SbCl₅ affords dimeric bis(hexachloroantimonate) bearing two pyrano[3,4-c]pyran7-ium moieties linked via oxygen atom. The crystal structures of both isolated products have been determined.