3-Benzoxepin
3-Benzoxepin is an annulated ring system with an aromatic benzene ring and a non-aromatic, unsaturated, oxygen-containing seven-membered heterocyclic oxepin. The first synthesis was described by Karl Dimroth and coworkers in 1961. It is one of the three isomers of the benzoxepins.
Occurrence and synthesis
3-Benzoxepin itself is a non-natural compound, but the bicyclic ring system is part of the naturally occurring compounds perilloxin from Perilla frutescens, tenual, and tenucarb from Asphodeline tenuior. Perilloxin inhibits the enzyme cyclooxygenase with an IC50 of 23.2 μM. Non-steroidal anti-inflammatory drugs like aspirin and ibuprofen also work by inhibiting the cyclooxygenase enzyme family.Unsubstituted 3-benzoxepin can be synthesized through a double Wittig reaction from o-phthalaldehyde with bis--dimethylether-dibromide. The latter compound can be synthesized from α,α′-dibromodimethyl ether which is accessible from hydrobromic acid, paraformaldehyde, and triphenylphosphine. The reaction is performed in dry methanol with sodium methoxide, and the product is obtained in 55% yield.
The compound can also be obtained through UV-irradiation of certain naphthalene derivatives such as 1,4-epoxy-1,4-dihydronaphthalene.
It can also be obtained by photooxygenation of 1,4-dihydronaphthalene, followed by pyrolysis of the formed hydroperoxides.
The latter syntheses give 3-benzoxepins in low yields.