ELECTROPHILIC SUBSTITUTION OF METHYLENE-BRIDGED POLYCYCLIC AROMATIC-HYDROCARBONS

The electrophilic bromination and formylation of the methylene-bridged polycyclic aromatic hydrocarbons 11H-benz[bc]aceanthrylene (2), 4H-cyclopenta[def]chrysene (3), 13H-dibenz[bc,l]aceanthrylene (4), and 4H-benzo[b]cyclopenta[mno]chrysene (5) were investigated. All reactions proceeded with high regioselectivity to afford predominantly a single major isomeric product. The sole exception was bromination of 3 which gave a small amount of a second isomeric product. The sites of electrophilic substitution were correlated with theoretical predictions from semiempirical molecular orbital calculations using the MNDO method, The observed sites of electrophilic substitution were in excellent agreement with the theoretical predictions in the cases of 2-4. However, in the case of 5, substitution took place in the 6-position, whereas the site predicted to be most reactive is the 5-position. In addition, the aryl aldehyde products were converted into the corresponding methyl derivatives for studies of their potential carcinogenicity.