On diastereomeric perturbations

For more than a century, organic chemists have been playing in Nature's lab oratory. Their first goal was to understand the organization of atoms in th e living matter and then to reproduce it by synthesis. This quest gave rise to several efficient techniques to synthesise molecules; many of them stil l in use nowadays, as such or with little modifications. Even at the beginn ing of this journey, the chemists discovered that their methods were far fr om being as efficient as the ones used by Nature to produce substances. The natural molecules were chiral and there was even an enantiomer that was pr oduced over the other;a lesson of perfection. This was another challenge fo r the chemists and they succeeded by first developing techniques to separat e enantiomers and more recently reagents and reactions to produce only the desired stereoisomer. Asymmetric synthesis uses chiral auxiliaries, reagent s or catalysts to create chirality into the desired compound. The common pe rception, as a minimum condition, was that the chiral substance used to per form such a transformation has to be of the highest enantiomeric purity to obtain a very high selectivity. The relation between the enantiomeric exces ses of the chiral substance and the product was suggested to be linear. But there were a lot of surprises left in the laboratory. Who would have thoug ht that an impure substance could give an enantiomeric excess in the produc t higher than its own purity? The molecules are acting in different ways in solution. Self-organization and aggregation can arise depending on the str ucture of the substance or its environment. Such phenomenon can generate de viations to the awaited behaviour of the molecules that can be observed in many cases. This article tries to present some examples of the historical r eports of such peculiar behaviours, their influence on physico-chemical pro perties and the final discovery of the now well-known nonlinear effects in asymmetric synthesis.