Distortion of Olefin and Carbonyl ?-Orbitals in Dibenzobicyclooctatrienes and Dibenzobicyclooctadienones. Unsymmetrization of ? Lobes Arising from ?-? Orbital Interactions

Article abstract of DOI:10.1021/jo00093a032

We have detected the unsymmetrical ? faces of the olefin group in 2-substituted dibenzobicyclo<2.2.2>octatrienes (2-substituted 9,10-dihydro-9,10-ethenoanthracenes) and the carbonyl groups of 2-substituted and 3-substituted dibenzobicyclo<2.2.2>octadienones (2-substituted and 3-substituted 9,10-dihydro-9,10-(11-ketoethano)anthracenes), wherein ?-type overlaps of the ? orbitals are involved, in a similar manner to longicyclic conjugation.An intrinsically nonequivalent substituent at distal positions modulates the epoxidation and dihydroxylation of the olefin group and the reduction of the carbonyl group.Both systems exhibit similar substituent effects: an "electron-withdrawing" substituent such as a nitro or fluoro group gave a large to moderate bias (preferred syn attack with respect to the substituent) whereas an "electron-donating" methoxy substituent exhibited a negligible bias.Herein we interpret these biases or nonbiases in terms of unsymmetrization of ? lobes of the olefin and carbonyl ? orbitals, arising from nonequivalent ?-? interactions rather than from an electron-donating or -withdrawing effect.