Thermal Isomerization of 12‐Oxa‐1,9‐dimetylhexacyclo[7.2.1.0 2,4 .0 2,8 .0 3,7 .0 6,8 ]dodec‐10‐ene: A Computational Mechanistic Investigation

Flash‐vacuum pyrolysis of the quadricyclane derivative 5a at 350° 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.