Photochemical transformations. 45. Orbital overlap preferences in excited-state intramolecular electron transfers

Syntheses of a number of meta-methoxy-substituted 2,3;6,7-dibenzobicyclo(2.2.2)octadienes, substituted as well on the ethano bridge, have been carried out. These included the four acetates produced by Diels-Alder reactions between 2-methoxyanthracene and vinyl acetate. The acetates were converted to alcohols and to methanesulfonates. The isomer with the anti-homopara relationship between the methoxy group and the carbon bearing the methanesulfonate group was substantially more reactive than the other three isomers, which had approximately equivalent reactivities. /sup 1/H NMR spectra were used to confirm structures of all compounds, and typical anti migrations were observed. Mixture compositions matched those anticipated from relative reactivities. Irradiations of the methanesulfonates were conducted in acetic acid-acetonitrile with 300-nm light. Of the four isomers, only the one with the anti-homometa relationship between the methanesulfonate group and the ring methoxy substituent was photoactive. All four isomeric dichlorides were photoactive (300-nm light in acetic acid), giving photo-Wagner-Meerwein rearranged chlorides and acetates. The two isomers with anti-homometa chlorine atoms were considerably more photoactive than the other two.