Chiral Lewis Acid - Theory

Theory

The enantioselectivity of CLAs derives from their ability to perturb the free energy barrier along the reaction coordinate pathway that leads to either the R- or S- enantiomer. Ground state diastereomers and enantiomers are of equal energy in the ground state, and when reacted with an achiral lewis acid, their diastereomeric intermediates, transition states, and products are also of equal energy. This leads to the production of racemic mixtures of products. However, when a CLA is utilized in the same reaction, the energetic barrier of formation of one diastereomer is less than that of another – the reaction is under kinetic control. If the difference in the energy barriers between the diastereomeric transition states are of sufficient magnitude, and high enantiomeric excess of one isomer should be observed (Figure 2).