Curtin-Hammett principle: application to benzene oxide-oxepin tautomers

The very rapid benzene oxide/oxepin equilibrium plays an important role in the metabolism of benzene by cytochrome P450. Although it is the benzene oxide valence tautomer that is attacked by nucleophiles and rearranges to phenols in acidic media, it is the oxepin valence isomers that suffer one-electron oxidation. However, some other reactions are more competitive and also furnish useful illustrations of the Curtin-Hammett principle. For example, while oxepin and benzene oxide are comparable in energy, the only reaction product with maleic anhydride is the Diels-Alder adduct with benzene oxide. Density function theory (B3LYP/6-31G*) calculations are employed for study of three sets of benzene oxide/oxepin equilibria and Diels-Alder reactions with maleic anhydride and dimethylazodicarboxylate as well as epoxidation by dioxirane. Comparisons are made between theory and published experimental data.