Selectivity-determining transition structures for the (S)-VANOL aluminate catalyzed epoxidation reaction. For a direct comparison to the boron catalyst, we conducted a comprehensive conformational search for the rate-and enantioselectivity-determining ring-closing TS for both the BLA and LA pathways in the epoxidation reaction catalyzed by the aluminum catalyst. The lowest energy transition structures leading to the experimentally observed major (S,S) and minor (R,R) enantiomer of cis-24a in both these pathways are shown in Figure . The four TSs shown in Figure are very similar in geometry to the analogous TSs shown in Figure . However, remarkably and consistent with the experimentally observed enantiodivergence, our calculations show that TSRC-Al-BLA-maj (the ring-closing TS that gives (S,S)-24a) is now the lowest energy TS for the reaction with the aluminum catalyst. Intriguingly, the lowest energy TS leading to the minor (R,R) enantiomer proceeds via the LA activation pathway -TSRC-Al-LA-min is 1.8 kcal/mol higher in energy than TSRC-Al-BLA-maj, a value that is in good agreement with the 81% ee observed for this reaction (Table ). Analysis of the key interactions stabilizing the aluminum TSs (Figure ) reveals that they are very similar to the corresponding interactions in the analogous boron TSs (Figure ). Therefore, the reversal in the sense of asymmetric induction upon switching from boron to aluminum must have its origins in the relative energetic contributions of these stabilizing interactions in the two catalytic systems.