Photochemical Studies. On the Photofragmentation of Substituted 1,2-Dihydrophthalic Anhydrides

Article abstract of DOI:10.1021/jo00339a030

The irradiation-induced transformations of 4,5-diphenyl-1,2-dihydrophthalic anhydride (2b) as well as those of the 3,6-dimethyl-4,5-diphenyl and 3,4,5,6-tetraphenyl derivatives (2c,d) are elaborated.All undergo photofragmentation, viz., CO + CO2 ejection to give aromatic hydrocarbons, while only 2b also closes electrocyclically to the bicyclo<2.2.0>hex-5-ene product 5.The quantum yields for fragmentation are indicative in this respect.The rearrangement accompanying the fragmentation of 2d to give 1,2,3,5-tetraphenylbenzene (11) was shown to occur via a triplet excited state, populated by benzene sensitization.