the novel heterobicyclic compounds 4. As demonstrated by the examples of their reactions with nonacarbonyldiiron(0) and the pentacarbonyltungsten fragment, compounds 4 are able to function as ligands in complex compounds. In addition, the electron-rich double bond in the bicyclic compound 4a is amenable to further reactions. Hence, treatment with mesitylenecarbonitrile oxide (7) proceeds through a chemo-