Origin of enantioselectivity and enantiodivergence observed in the (S)-VANOL aluminate/boronate catalyzed epoxidation rection: A comparison of the transition structures leading to (S,S)-24a for the boron catalyst (Figure , TSRC-B-BLA-min) and the aluminum catalyst (Figure , TSRC-Al-BLA-maj) reveals that these structures are nearly identical in terms of the bond-forming/bond-breaking distances as well as the key stabilizing interactions. A similar conclusion can be drawn upon analysis of the corresponding transition structures leading to (R,R)-24a for the boron (Figure , TSRC-B-BLA-maj) and aluminum (Figure , TSRC-Al-BLA-maj) catalyst systems. Even though these pairs of analogous transition structures are near identical, the calculations predict that (R,R)-24a is the major enantiomer for the boron catalyst and (S,S)-24a is the major enantiomer for the aluminum catalyst (Figures and) -consistent with the experimentally observed enantiodivergence observed across the two catalyst systems. Qualitatively, these observations suggest that the identity of the central Lewis acidic atom (B/Al), the difference in polarization and bond-lengths of the metal-oxygen bonds in the two metalate species likely play important roles in the observed enantiodivergence in these catalyst systems. The effects of these subtle differences in catalyst properties must stabilize the exact same transition state differently. In order to evaluate the origin of enantioselectivity in each of these catalyst systems, we conducted an energy decomposition analysis of the transition structures leading to the major and minor enantiomer of cis-24a for the BLA mechanism (the first two structures from the left in Figures and). An energy decomposition analysis 20 comparing TSs leading to the two enantiomers of product provides quantitative insight into the origin of the observed enantioselectivity by separating the effects of distortion (catalyst and substrate distortion from lowest energy conformation) and interaction (H-bonding, dispersion etc.) energies to transition state stabilization. The summary of this analysis are as follows -(a) comparison of the interaction energies reveals that both catalysts favor the (S,S) enantiomeraluminum by 3.7 kcal/mol and boron by 0.7 kcal/molsince the (S,S) TS in both cases is characterized by conventional H-bonding interactions, the more polarized Al-O bond provides more stabilization via the stronger Hbond. (b) The major contributor to the observed enantiodivergence is the effect of catalyst/substrate distortion -the (S,S)-enantiomer pays a lower energetic penalty from distortion compared to the (R,R)-enantiomer (favored by 2.8 kcal/mol) for the aluminum catalyst while the reverse is true for the boron catalyst ((R,R)-enantiomer favored by 1.6 kcal/mol for the boron system). A possible explanation for this reversal in the trend of distortion interactions could be gleaned by visual analysis of the TS leading to the (S,S)-enantiomer in the boron (Figure , TSRC-B-BLA-min) and aluminum (Figure , TSRC-Al-BLA-maj). It is likely that the longer Al-O bond places the VANOL ligand farther away from the chiral pocket compared its position with the boron catalyst and the shorter B-O bond. As a result, the diazoacetamide portion of the transition state has to distort less in TSRC-Al-BLA-maj compared to TSRC-B-BLA-min in order to avoid deleterious steric interaction with the VANOL backbone. In summary, the switch from boron to aluminum as the central metal results in a reversal of the sense of enantioselectivity because of change in the steric features of the chiral pocket as well as the electronic properties of the H-bond acceptor oxygen atoms that flank the central atom (B/Al). The full details of the energy decomposition analysis can be found in the Supporting Information. Synthesis of (-)-Tedanalactam: With the initial success of the epoxidation of aldehyde 2a with the aluminum catalyst (Table ), the epoxide 13 was then taken on to tedanalactam 5 and this is when it was first realized that the boron and aluminum catalysts give opposite enantiomers in the epoxidation reaction -the rotation (aD:7.1) did not match that reported for the natural product (aD:-7.6). This was of course rectified by switching to the (R)-VAPOL aluminum catalyst as indicated in Scheme 4. The aldehyde 2a is commercially available but is very expensive and thus was prepared as indicated in Scheme 4 from 1,3propanediol following the procedure of The epoxide 13 is then deprotected to give the 1° alcohol 44 which is then converted to the 1° tosylate and then directly cyclized with sodium hydride to give the 3,4epoxy-2-piperidone 45 in 67% yield. If the tosylate is first isolated the yield for this sequence drops to 47%. Deprotection of the lactam nitrogen in 45 can be effected with ceric ammonium nitate to give (-)-tedanalactam in 75% yield.