Skeletal Rearrangement of Twisted Polycyclic Aromatic Hydrocarbons under Scholl Reaction Conditions

Treatment of a twisted polycyclic aromatic hydrocarbon containing cyclooctatetraene fused by two 9,9′-bifluorenylidene units under the Scholl reaction conditions (FeCl₃ or 2,3-dichloro-5,6-dicyano-1,4-benzoquinone and scandium trifluoromethanesulfonate) led to stepwise skeletal rearrangements to afford initially a hydrocarbon with a seven-membered ring and then tetrabenzo­[a,d,j,m]­coronene with all six-membered rings. The course of the rearrangement was interpreted in terms of the acid-catalyzed isomerization of 9,9′-bifluorenylidene into dibenzo­[g,p]­chrysene moieties on the basis of theoretical investigations.