Exceptional dimerisation of 7,9-dimethylcyclopent[a]acenaphthylen-8-one; X-ray crystal structure of the diol–diacetate of one of the dimeric products

Abstract

In solution at 20 °C the cyclopentadienone (1) is in equilibrium with the normal endo-Diels–Alder dimer (2) and the formal [π2 +π2]-dimer (3) the structure of the diol–diacetate of which has been determined by X-ray crystallography; on heating at 80 °C this mixture affords the exo-Diels–Alder dimer (4).