4-Acetoxytricyclo[4.1.0.02,7]Hept-4-en-3-one; synthesis and novel bond reorganization of a valence isomer of 2-acetoxytropone

4-Acetoxytricyclo4.1.0.0^2,7]hept-4-en-3-one ($\text{3}$), a valence isomer of 2-acetoxytropone, was synthesized. Upon heating in pyridine at 150°C, $\text{3}$ rearranged into 1-acetoxybicyclo3.2.0]hepta-3,6-dien-2-one ($\text{9}$); the mechanism of which was examined by means of deuterium labeling experiments.