PHOTO-CHEMICAL OXIDATION AND REARRANGEMENT OF DIBENZOBARRELENE AND DEHYDROJANUSENE

Dibenzobarrelene (1) and dehydrojanusene (2) are unreactive toward singlet oxygen under photosensitization with tetraphenylporphin (TPP), methylene blue (MB), or rose bengal (RB) in visible light. With a medium-pressure mercury vapor lamp, 2 gives a minor amount of epoxide and extensive di-π-methane rearrangement into 6, whose structure was established by X-ray diffraction analysis. 6 was obtained in high yield by photosensitization with benzophenone or acetone; with acetone as solvent an addition product of ketone to hydrocarbon 6 (but not to 2) was also formed, for which structure 10 is suggested. In mixtures, the rearrangement of 2 was 1.5-2.0 times as fast as the known rearrangement of 1 to 8. Biacetyl and benzii photosensitize the epoxidation of both 1 and 2 to photounstable epoxides. Under the epoxidation conditions, the epoxide from 1 is converted into substantial amounts of anthraquinone. Under the conditions of photoepoxidation, anthracene (also observed in these reactions) is oxidized to anthraquinone along with some carboxylic and phenolic products. © 1979, American Chemical Society. All rights reserved.