In this reaction, we see a degenerate [3,3] shift from a boat conformation of the cycloheptane ring. The boat structure and the transition state for the reaction are shown below, with their energies.
Energies calculated at the HF/6-31G* level with ZPE correction.
boat structure
transition state structure
The transition state is 61 kcal/mol above the boat conformation, which is itself about 3 kcal/mol above the chair conformation. However, the reaction cannot take place from the chair conformation of the cycloheptane ring.