Electronic and structural chirality of prochiral centres in chiral molecules. A non-steric contribution in stereoselective reactions

Abstract

Prochiral centres of local C 1h symmetry may undergo addition reactions leading to the destruction of the reflection plane and consequently the formation of a new chiral centre. The chirality of the product is determined by whether the attack is from above or below the plane, so that a hypothetically isolated prochiral centre would lead to equal amounts of the two forms of the chiral product. It is shown, however, that prochiral centres in chiral molecules are, strictly speaking, electronically and structurally chiral even prior to addition because of long range electronic coupling between the prochiral centre and the other parts of the molecule. The nature of the perturbations leading to such chirality are derived, and the role of this induced chirality in leading to stereoselectivity (i.e. favoured attack from one side of the plane) discussed.