Les effets non linéaires en catalyse asymétrique

Asymmetric catalysis using an enantio-enriched catalyst to induce chirality in the synthesis of a substance of interest is the strategy of choice to produce this substance with the highest enantiopurity. From then on, it is generally accepted that enantiomeric purity of the catalyst to perform this transformation was a guarantee for obtaining high enantioselectivity. Indeed, the relationship between the enantiomeric excess of the chiral catalyst used and that of the reaction product is considered linear. However, this is not always the case as shown by various laboratory experiments. An enantiomerically impure chiral substance can give rise to a product whose enantiomeric purity is higher than its own, a phenomenon that is qualified as a non-linear effect. Understanding these asymmetric amplification phenomena is essential not only to understand the intimate mechanisms of the reaction, but also to contribute to the debate on homochirality in life, as enantioselectivity allows nature to perform most of the biological functions essential to life. Tracing historical elements to the most recent discoveries, this article presents the various mechanisms that can lead to these non-linear effects. It also contextualizes the major contribution of Henri Kagan in the discovery and understanding of these phenomena.