Why does the 6-endo intermediate rearrange into the 5-exo product? We turned to computational studies using the ORCA DFT software package to rationalize the observed preference for a rearranged 5-membered ring 73 versus the initially formed 6-membered ring 72. All calculations were performed using the B3LYP functional with D3BJ dispersion correction using the RIJCOSX approximation. The def2-TZVP basis set was used, and implicit THF solvation was applied using the SMD model. The def2-ECP was applied automatically to mercury replacing 60 core electrons. Further details and atomic coordinates are reported in the Supporting Information.