Equilibrium structural parameters of didehydrobullvalene, its adducts with furan, and tris(didehydrobullvalene) and bullvalenophenol tautomers have been determined by DFT M06-2X/cc-pVTZ quantum chemical calculations. The energies of the assumed Diels-Alder adducts are considerably higher than the energies of the isolated products, and the energy barriers separating them are fairly low. Interconversion of enantiomers of the major adduct via two sequential Cope rearrangements with calculated barriers of 17.2 and 15.0 kcal/mol, respectively, may be regarded as an example of truly degenerate mediated tautomerism.