Review Chiral resolutions, asymmetric synthesis and amplification of enantiomeric excess

Abstract

The notion of molecular chilarily is important from both a theoretical standpoint, and a practical point of view. Chemists therefore showed an early interest in :the development of methods for the production of chiral substances, andthe origin of optical activity.This review describes and compares the performance (in terms of enantiomeric excess versus yield) of the main types of chiral resolution and asymmetric synthesis used either in the laboratory or industrially. Mathematical relationships which can be used practically in kinetic studies are also presented.The role and relative importance of the main natural chiral factors that might have played a role in the origin of optical activity are also discussed. The process of the amplification of enantiomeric excess can be analysed both theoretically and experimentally. Most of the theoretical models consist of general kinetic schemes involving stages of autocatalysis and mutual inhibition. Their kinetic behaviours are analysed in terms of concepts drawn from non-linear chemical dynamics. It is demonstrated that under certain conditions the racemic state is unstable. During a critical period the course of evolution of the system is thus particularly sensitive to small external perturbations.The experimental studies to date involve either polymerisations (polycondensations) or mutual inhibitions (crystallisation of racemates, steroeselective reactions etc.). Their realm of practical application is thus relatively limited.Suggestions are made for the integration of some useful theoretical concepts into current laboratory practice. It is to be hoped that they might form a basis for further improvements in the performance of experimental systems.