title: Orbital Unsymmetrization Affects Facial Selectivities of Diels-Alder Dienophiles.
abstract: We investigated the Diels-Alder reactions of maleic anhydrides embedded in a dibenzobicyclo[2.2.2]octatriene motif as a nonsterically biased dienophile. Substituents on a benzene ring in these dienophiles are far from the reaction center, providing a sterically equivalent pi-face. Instead substituents can unsymmetrize the dienophilic pi face through pi (anhydride)-pi (aromatic) orbital interactions. Electron-withdrawing substituents affect the facial bias and relative rates of these cycloadditions. The preference of the cycloadditions is opposite in direction to those observed in nucleophilic additions of 2-substituted-9,10-dihydro-9,10-ethanoanthracen-11-ones (dibenzobicyclo[2.2.2]octadienones) and in electrophilic additions of 2-substituted 9,10-dihydro-9,10-ethenoanthracenes (dibenzobicyclo[2.2.2]octatrienes), though all of them have related dibenzobicyclic systems.
authors.affiliation: Faculty of Pharmaceutical Sciences, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113, Japan.
authors.forename: Iwao
authors.initials: I
authors.lastname: Okamoto
authors.forename: Tomohiko
authors.initials: T
authors.lastname: Ohwada
authors.forename: Koichi
authors.initials: K
authors.lastname: Shudo