Oxabicyclo 2.2.1 heptadienes

In the UV absorption spectra of the 7-azabicyclo[2.2.1]heptadiene-2,3-diesters (11)-(14), a maximum or shoulder between 290-300 nm (e 10 ) is attributable to interaction between the homoconjugated double bonds.This band is absent from the spectrum of the 5,6-dihydro derivative (25), but absorption in the same position has been recorded for similarly substituted 7-oxabicyclo[2.2.1]heptadiene derivatives. ... 

The stereochemistry of addition of a variety of electrophilic reagents to 7-oxabicyclo[2.2.1]heptadiene derivatives has been described in a... 

From Benzo-7-oxabicyclo[2.2.1]heptenes, Benzo-7-oxabicyclo[2.2.1]heptadienes, and Related Compounds... 

Furans react with electron-deficient alkynes giving 7-oxabicyclo[2.2.1]heptadienes (30). Whereas it is possible to induce thermally a retro cycloaddition <62ioc3520.89CC1238>, normally these intermediates are reduced at the less hindered side, yielding 7-oxabicyclo[2.2.1]heptenes (31) (Scheme 30). Elimination of ethylene (Alder-Rickert reaction <37CB1354> yields substituted furans (Scheme 30) <6814501, 85JHC1233, 87BSF131>. 

Cycloadducts of 7-oxabicyclo[2.2.1]heptadienes with nitrile oxides or tetrazines may undergo a cycloreversion giving furans and isoxazoles (pyridazinones) <72CC2i 1,74TL2163). Oxazoles react with alkynes to give 2-aza-7-oxabicyclo[2.2.1] heptadienes (32), which lose a nitrile spontaneously by a cycloreversion reaction yielding furans (Scheme 31). 

Due to the instability of the seven-membered heterocyclic ring, oxepin is prone to isomerization reactions to bicyclic heterocycles such as benzene oxide. Irradiation of oxepin with UV light of/. > 310 nm gives the isomeric 2-oxabicyclo[3.2.0]heptadiene(l) in high yield.12 207 At shorter wave lengths, phenol is formed predominantly.207... 

Under irradiation in diethyl ether, the dextrorotary enantiomer of 3,6-hexanooxepin-4-carb-oxylic acid rearranges to the oxabicyclo[3.2.0]heptadiene system with retention of the optical activity.36... 

Copper (I)-catalyzed intramolecular photocycloaddition between two acycHc double bonds was first observed by Evers and Mackor in 1978. They demonstrated that although 3-oxabicyclo[3.2.0]heptane 26 is formed from diallyl ether 25 (Scheme 8), 4-hydroxy-1,6-heptadiene 27 produces an endo,exo (3 2) mixture of 3-hydroxy bicyclo[3.2.0]heptanes 28 (Scheme 9) on irradiation in presence of CuOTf. The generahty and scope of this reaction were investigated in great detail by Salomon et al. The acyclic dienes... 

---