The endo-cis adducts were selectively obtained by the Diels-Alder reaction of several dienes with bicyclo[3.2.2]nona-3,6-dien-2-one, prepared from tropone and ethylene. This selective formation from the bicyclic dienophile, the isolated C=C and ethano C–C bonds of which are situated in similar sterical environments within the molecule, was supported by an Extended Huckel calculation.