Unusual formation of tricyclic annulenediones: diatropic cationic 10π-electron species in D2SO4

Abstract

Intramolecular oxidative coupling of 1-(3-oxopent-1-en-4-ynyl)-6-(1-oxoprop-2-ynyl)cyclohepta-1,3,5-triene 2 under the Glaser conditions unexpectedly afforded two tricyclic annulenediones. The unusual structures were determined by X-ray crystallographic analysis of the compounds. These annulenediones are atropic in CDCl₃, but exhibited diatropicity in CF₃CO₂D and D₂SO₄ ascribable to the formation of cationic 10π-electron species.