Photochemistry of Phenyl-Substituted Benzobicyclohex-2-enes. A Reverse Di-?-methane Rearrangement

Article abstract of DOI:10.1021/jo00161a014

The photochemical rearrangements of phenyl-substituted benzobicyclo<3.1.0>hex-2-enes can generally be explained by assuming that homolytic fission of that cyclopropane bond which leads to the most stable diradical is the primary step.The final products are formed by 1,2 hydrogen shifts in the intermediate.An exception to this general pattern was observed with 5-phenylbenzobicyclo<3.1.0>hex-2-ene (5).The photoproducts of 5 could only be explained by assuming reverse di-?-methane rearrangements followed by 1,3 hydrogen shifts.It is argued that this reaction path is followed because of the high rate to the back-reaction of the homolytic bond fission of 5.