Electrophilic Substitution of Polycyclic Fluoranthene Hydrocarbons

Article abstract of DOI:10.1021/ja00193a008

The first systematic study of the sites of electrophilic substitution (acylation and/or bromination) of polycyclic fluoranthene hydrocarbons is described.The hydrocarbons studied include indeno<1,2,3-cd>pyrene (1), benzaceanthrylene (2), benzacephenanthrylene (3), and indeno<1,2,3-hi>chrysene (4).Compounds 1-4 all undergo bromination regioselectively in a single site.The latter are determined by conversion of the bromo derivatives to monodeuterio analogues by metal exchange with butyllithium and analysis of their high-resolution 1H and 13C NMR spectra in comparison with those of the parent hydrocarbons.This method is potentially generally applicable to determination of the sites of substitution of other complex polycyclic hydrocarbon ring systems.Acylation of 1 is shown to take place in the same site as bromination, i.e., the 12-position.For 2 and 4, substitution occurs in the 8- and 5-positions, respectively, in good agreement with theoretical prediction by the DEWAR-PI method based on the relative energies of the Wheland intermediates for substitution at various ring positions.However, for 1 and 3 the principal sites of bromination observed experimentally are the 12- and 1-positions, respectively, which do not accord with theoretical prediction of the 3,5- and 8-positions, respectively.In the latter cases, the observed sites of bromination are only slightly less favorable energetically than the theoretically calculated sites and are probably within the limit of accuracy of the calculations.