Dimethyl oxaquadricyclane-2,3-dicarboxylate (1) with cyclooctyne (CO) gave,
via carbonyl ylide (3a), a mixture of the exo and endo 1:1 adducts (2a, 2b
) along with the novel 1:2 adduct (2c), whereas the carbocyclic analogs und
erwent [sigma 2s + sigma 2s + pi 2s]cycloaddition. The first examples of in
verse electron demand homo-Diels-Alder reactions of oxa-, aza- and carbo-no
rbornadienes with CO were also described.