The Thermal Isomerizations of Bicyclo[2.1.0]pent-5-yl Methyl Ketones: endo-exo stereomutation and cyclopropyl-allylic rearrangement to cyclopent-2-enyl methyl ketones

Bicyclo[2.1.0]pent‐5‐yl methyl ketones undergo two thermal isomerization reactions. The endo‐exo stereomutation follows the ring‐flip path in better than 90%, with inversion of the configuration of the angular carbon atoms by cleavage and reclosure of the central bond. Stereomutation and cyclopropyl‐allylic rearrangement to cyclopent‐2‐enyl methyl ketone do not involve a common intermediate and proceed on separate potential energy surfaces. The activation parameters of the rearrangement suggest an allowed concerted cycloreversion process.