Generation and Reactions of Pentacyclo[4.3.0.0^2,4.0^3,8.0^5,7]non-4-ene

The highly pyramidalized alkene, pentacyclo[4.3.0.02,4.03,8.05,7]non-4-ene (9), has been generated via treatment of 4,5-diiodopentacyclo[4.3.0.02,4.03,8.05,7]nonane (12) with n-butyllithium and tert-butyllithium. The title alkene has also been trapped as its Diels−Alder adduct with 1,3-diphenylisobenzofuran, 2,5-dimethylfuran, and spiro[2.4]hepta-4,6-diene. Products resulting from alkyllithium addition to the pyramidalized double bond of 9 have been isolated and fully characterized spectroscopically. The geometry, olefin strain energy, heat of hydrogenation, and relative HOMO/LUMO energies of 9 have been obtained by ab initio calculations at the MP2 and B3LYP levels using the 6-31G* basis set.