The structure and the stereochemistry of the mono-adducts, obtained by 1, 3-dipolar cycloaddition of nitrile oxides to cyclooctatetraene, have been elucidated on chemical evidence. Thermolysis of their Diels-Alder adducts with acetylenedicarboxylate yielded 4- aryl (or alkyl)-2, 3-oxazabicyclo [3.2. 0] hepta-3, 6-dienes. Some reactions of this new heterocyclic condensed system are described.
![3-methyl-(3ac,3bt,7at,7bc)-3a,3b,4,7,7a,7b-hexahydro-4r,7c-etheno-benzo[3,4]cyclobuta[1,2-d]isoxazole-5,6-dicarboxylic acid dimethyl ester Structure](https://image.chemsrc.com/caspic/437/30286-97-6.png)
![2-methyl-4-oxa-3-azabicyclo[3.2.0]hepta-2,6-diene Structure](https://image.chemsrc.com/caspic/192/31007-58-6.png)
![3-methyl-(3ar,3bt,7at,7bc)-3a,3b,7a,7b-tetrahydro-benzo[3,4]cyclobuta[1,2-d]isoxazole Structure](https://image.chemsrc.com/caspic/213/30286-90-9.png)