Stereochemical Model. Having used statistical modeling, reaction kinetics, catalyst structural studies, and DFT calculations as complementary tools to interrogate this transformation, a stereochemical model can be proposed. According to our mechanistic model, the sulfonimidamide substituent is placed pseudo-equatorially in the 6-membered ring transition state leading to the preferred (S)-enantiomer. Smaller substrates in the transition state will have a lower preference for the sulfonimidamide substituent being placed pseudo-equatorially versus pseudo-axially ((S)-12, Figure ), leading to selectivity erosion. However, larger substrates in the preferred pseudoequatorial position will lead to unfavorable steric interactions with the phosphinate substituents ((R)-12, Figure ). To identify substrates for which it is difficult for the catalyst to impart selectivity, we further investigated the steric terms in the original statistical model (Figure ). We plotted the substrate volume against the catalyst buried volume and overlaid the measured ΔΔG ‡ as a heatmap (Figure ). It confirms that the catalyst pocket is not amenable to small (<1000 Bohr ra-dius³/mol; 1k and 1l) nor large (>1490 Bohr radius³/mol; 1i, 1g, 1h, 1q, 1j) substrates.