The temperature was set to be 300.0 K. The 𝐸 LMN ‡ and 𝐸 LPQN ‡ are the electronic energies of (exo)-TS and (endo)-TS, respectively. According to this equation, the exo selectivity was calculated to be 32.5%, which is slightly underestimated comparing to the experimental result using PPh3 (68%). With the structure of (endo)-TS and (exo)-TS in hand, we then performed the differentiation of the electronic energy, and the derivative of the exo selectivity in terms of VL parameters was calculated (see SI for the detailed formulation). The derivative values with respect to parameters a1, a2, b1, b2, c1, c2 and r0 were shown in Figure (right). The positive derivative values for steric parameters (a1, a2, b1, b2, c1 and c2) imply that the exo selectivity can be improved by increasing the steric bulk of the substituent.