1,3-Dipolar cycloaddition of nitrile oxides with symmetrical tri- and polycyclic strained olefins

1,3‐Dipolar cycloadditions of benzonitrile oxide and carbethoxyformonitrile oxide (CEFNO) with various facially perturbed polycyclic symmetrical dienophiles (1, 1a, 1b, 2, 2a, 2b, 3, 3b, 4, 5, 6) were investigated. Cycloadditions took place chemoselectively at the norbornyl double bond and were found to be exclusively exo. Cycloadditions of benzonitrile oxide with dienophiles 4 and 5 led to mixture of inseparable products, however, that with CEFNO gave single products. Cycloadduct of dienophile 5 with CEFNO was found to be unstable, and it readily isomerized to more stable aromatic form. J. Heterocyclic Chem., (2010).