In order to reveal the difference in interaction energies between the substrates and the catalyst (ΔΔEint), the non-covalent interaction (NCI) analysis of the TS structures was conducted, which enabled the visualization of the non-covalent interactions. The NCI analyses of TSwyn2A(S) and TSwyn2A'(R) reveal that, in addition to the strong conventional N + -H and C-H•••π 48 interactions are present. Most interestingly, there is a favorable π•••π stacking interaction between the additive and the electrophile, which also contributes to the stabilization of both TSwyn2A(S) and TSwyn2A'(R) (see Fig. and S11 in SI). As the substrates and additive interact with the catalyst through a network of hydrogen bonding interactions, as well as through a π•••π stacking interaction, it is still not easy to figure out which factors are the major ones contributing to the ΔΔEint. In order to understand the factors involved, it is therefore also necessary to quantify the weak interactions in the transition state structures.