Dedicated to Professor Rolf Huisgen on the occasion of his 85th birthday Flash-vacuum pyrolysis of the quadricyclane derivative 5a at 3508 afforded the oxabishomocubane 9a, whose structure was confirmed by an INADEQUATE-NMR experiment. A computational investigation of the mechanism of this unexpected reaction by DFT and CASPT2-SCF methods indicated that the reaction path of lowest energy involves a quadricyclane/oxaquadricyclane (5/12) isomerization, followed by a well-established cycloreversion of 12 to the carbonyl ylide 16, which subsequently undergoes an intramolecular 1,3-dipolar cycloadditon to 9. The lowest-energy path of the thermal isomerization of the syn-quadricyclane 6c is its conversion to the syn-sesquinorbornatriene 8c. The corresponding anti-isomer 5c, however, shows the capability of a degenerate quadricyclane/quadricyclane rearrangement.

1,6‐Dibromoquadricyclane (6) was obtained from norbornadiene (11) by hydroboration, oxidation of the diol 12 to the diketone 14 and its conversion into 2,6‐dibromonorbornadiene (20) using tribromodioxaphosphole 16b followed by treatment of the mixture 17/18 with potassium tert‐butoxide in DMSO and photocyclization of 20. Reaction of 6 with tBuLi (2 equiv.) led to the formation of 1‐bromo‐6‐lithioquadricyclane 7, the NMR spectra of which were observed up to 0°C. 7 did not lose LiBr to give 4, but could be trapped with H2O and chlorotrimethylsilane to give 21e (53%) and 21f (64%). Reaction of 6 with tBuLi (> 4 equiv.) gave rise to 1,6‐dilithioquadricyclane (21c), whose NMR spectra could also be recorded. 21c was converted into the corresponding 1,6‐disubstituted quadricyclanes with D2O (87%), chlorotrimethylsilane (92%), dimethyl sulfate (55%), methyl chloroformate (45%), iodine monochloride (62%), and p‐toluenesulfonyl chloride (48%). − Density functional calculations using the B3LYP‐6‐31G* level of theory showed that 1,6‐dehydroquadricyclane (4) is a local energy minimum in its singlet electronic state. 4 contains a unique structure with 4 condensed cyclopropane units. The parent hydrocarbons 27 and 28, hitherto unknown, are also local energy minima in their singlet electronic states.