Rearrangement of unsaturated cyclic peroxides obtained by photooxygenation of 2,3-dimethylene-7-oxabenzonorbornene and 2,3-dimethylene-1,4-etheno-1,2,3,4-tetrahydronaphthalene

Cobalt(II) tetraphenylporphyrin (CoTPP)-catalyzed rearrangement of peroxide 11 obtained by the photooxygenation of 5 gave a mixture of epoxides 15 (or 16) and 17. However, CoTPP-catalyzed rearrangement of peroxide 20 arising by photooxygenation of 2,3-dimethylene-1,4-etheno-1,2,3,4-tetrahydronaphthalane 6 gave 1,4-etheno-1,2,3,4-tetrahydronaphtho[b]-furan 21. The different behaviour of these endoperoxides 11 and 20 is discussed in terms of ring strain and the degree of the pyramidalization of the CC bond.