DISTORTION OF OLEFIN AND CARBONYL PI-ORBITALS IS DIBENZOBICYCLO[2.2.2]OCTATRIENES AND DIBENZOBICYCLO[2.2.2]OCTADIENONES - UNSYMMETRIZATION OF PI-LOBES ARISING FROM PI-PI-ORBITAL INTERACTIONS

We have detected the unsymmetrical pi faces of the olefin group in 2-s ubstituted dibenzobicyclo-[2.2.2]octatrienes (2-substituted 9,10-dihyd ro-9,10-ethenoanthracenes) and the carbonyl groups of 2-substituted an d 3-substituted dibenzobicycla[2.2.2]octadienones (2-substituted and 3 -substituted 9,10-dihydro-9,10-(11-ketoethano)anthracenes), wherein al pha-type overlaps of the pi orbitals are involved, in a similar manner to longicyclic conjugation. An intrinsically nonequivalent substituen t at distal positions modulates the epoxidation and dihydroxylation of the olefin group and the reduction of the carbonyl group. Both system s exhibit similar substituent effects: an ''electron-withdrawing'' sub stituent such as a nitro or fluoro group gave a large to moderate bias (preferred syn attack with respect to the substituent) whereas an ''e lectron-donating'' methoxy substituent exhibited a negligible bias. He rein we interpret these biases or nonbiases in terms of unsymmetrizati on of pi lobes of the olefin and carbonyl pi orbitals, arising from no nequivalent pi-pi interactions rather than from an electron-donating o r -withdrawing effect.