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.