4-Acetoxytricyclo[4.1.0.02,7]hept-4-en-3-one (), a valenceisomer of 2-acetoxytropone, was synthesized. Upon heating in pyridine at 150°C, rearranged into 1-acetoxybicyclo[3.2.0]hepta-3,6-dien-2-one (); the mechanism of which was examined by means of deuterium labeling experiments.