The endo-epimer of the formal homo-1,4 adduct of monochlorocarbene and norborna-2,5-diene on treatment with lithium 2,2,6,6-tetramethylpiperidide in THF in the presence of diphenylisobenzofurane (DPIBF) gave a single Diels-Alder adduct. The same cyclo-adduct was obtained by subjecting the homo-1,4 adduct of dibromocarbene and norborna-2,5-diene to lithiummethyl in THF. By single crystal X-ray analysis the adduct is shown to be the result of the normal Diels-Alder cyclo-addition of DPIBF to the least hindered side of tetracyclo[3.2.1.0.^2,70.^4,6]oct-2-ene, a novel anti-Bredt olefine, best considered as a carbon ylide.