Endoperoxide rearrangement

The bicyclic peroxide 11 was prepared via diimide reduction of the endoperoxide derived from spirocyclopentadiene (Eq. 8)21>. As before, at elevated temperature the labile endoperoxide rearranges into diepoxide and ketoepoxide,22) but diimide reduction at —78 °C allows trapping leading to the highly strained bicyclic peroxide 11. 

Isoprostane endoperoxide rearrangement yields gamma ketoaldehydes... 

Photooxygenation of azidoalkyl furans resulted in triazole formation and an endoperoxide rearrangement. The key step is a [3 + 2] cycloaddition of the azide to the endoperoxide intermediate, and the reduction of the peroxide bond and two subsequent C-C bond cleavages (13OL4790). 

In addition to photolytic or thermolytic conditions, the endoperoxide rearrangement to ihs-epoxides can also be conducted in a catalytic version in the presence of metaloporphyrins (e.g., cobalt(ll) tet-raphenylporphyrin). An illustrative difference between base-catalyzed (Kornblum-DeLaMare reaction) and thermal rearrangement of a cyclopentadiene-derived endoperoxide 13 was described recently. When... 

Akbulut, N., Menzek, A., and Balci, M., Thermolysis and CoTPP-catalyzed rearrangement of endoperoxides derived from 2.3-dihydro-l(2H)azulenone. A new endoperoxide-endoperoxide rearrangement. Tetrahedron. Lett., 28,1689, 1987. 

When the valence tautomeric mixture of oxepin and benzene oxide is treated with singlet oxygen, the primary product is the 1,4-endoperoxide 3 which has proven to be too labile for isolation.219 Its formation can be rationalized by a 1,4-addition across the diene system of the benzene oxide structure 3 then rearranges to ba s-3,6,9-trioxatetracyclo[6.1.0.02 4.05 ]nonane (transbenzene trioxide, 4). 

In this case, the benzene dioxide 5 is obtained from a [2,2]paracyclophane diene by photooxygenation and rearrangement of the derived endoperoxide. 

The strained dienic endoperoxide is readily reduced by diimide, leading to the relatively stable bicyclic peroxide in high yield. Again, aprotic solvents such as CH2C12 or CFClj are essential for the diimide reduction, because in MeOH complex rearrangements take place 30d e>. 

The endoperoxides (49) of oxazoles also undergo clean rearrangements following the path outlined in Scheme 6 <88TL1007>. The initial product is a dioxazole (50) identified at low temperature by NMR spectroscopy <90JCS(P1)1011>. Subsequent products are the imino anhydride (51) followed by... 

Scheme 7 Possible thermal rearrangement pathways of 2,5-dimethylthiophene endoperoxide.

The only examples of 1,2,4-trioxolanes containing A-linked substituents arise from photooxygenation of oxazoles. The endoperoxides thus produced are bicyclic, with a 1,2,4-trioxolane ring bridged by an imine moiety and are unstable at ambient temperature. They have been characterized at low temperature and thermal rearrangement is described in Section 4.16.5.1.1. 

A number of semibullvalenes and some barbaralanes, which undergo a facile Cope rearrangement via bicyclooctadienyl diradicals, produce various cyclic peroxides on exposure to triplet oxygen ". Thus, cyclopentano semibullvalene 82a is peroxidated with air to give a mixture of 5-membered 83a and 6-membered endoperoxide 84a in a 1 2 ratio, whereas the cyclohexano derivative 82b yields only the 6-membered cyclic peroxide 84b (Scheme 15). The energy in the highly strained mono(Dewar benzene) isomer of... 

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