Tandem Wagner-Meerwein rearrangement-carbocation trapping in the formation of chiral heterocyclic ring systems

Abstract

Ortho lithiated protected anilines and phenols undergo exclusive addition to fenchone from the exo face. The corresponding adducts, under acidic conditions undergo cationic rearrangement followed by internal trapping of the new cation with amino, hydroxyl or methoxyl substituents to give enantiomerically pure chiral heterocyclic ring systems. The nature of the rearrangement is dependent on the donor group and its ability to stabilise a positive charge. With an amino donor group a product due to Wagner-Meerwein rearrangement is formed while with a methoxy donor group Nametkin rearrangement is the preferred pathway.