REGIOSELECTIVITY IN THE DIELS-ALDER REACTION OF 9-SUBSTITUTED ANTHRACENES

The regioselectivity in the cycloaddition reactions of some 9-substituted anthracenes with acrylic acid, acrylonitrile, and allyl alcohol has been determined by 1H NMR analysis. The ortho regioisomer was preferred in all but two of the cases, the reactions of 9-nitro- and 9-carboxyanthracene with acrylic acid. The regioisomer ratios were found to remain constant over the course of the reactions; consequently, they are almost certainly of kinetic origin. The regioselectivity that was observed was predicted in ten out of the eleven reactions using CNDO/2 frontier molecular orbital energies and coefficients. The neglect of the first-order charge interactions or hydrogen-bonding effects could be the origin of the incorrect prediction. The regioselectivity could not be rationalized by a diradical mechanism nor by a localized charge mechanism. © 1979, American Chemical Society. All rights reserved.