TANDEM WAGNER-MEERWEIN REARRANGEMENT-CARBOCATION TRAPPING IN THE FORMATION OF CHIRAL HETEROCYCLIC RING-SYSTEMS

Ortho lithiated protected anilines and phenols undergo exclusive addit ion to fenchone from the exo face. The corresponding adducts, under ac idic conditions undergo cationic rearrangement followed by internal tr apping of the new cation with amino, hydroxyl or methoxyl substituents to give enantiomerically pure chiral heterocyclic ring systems. The n ature of the rearrangement is dependent on the donor group and its abi lity to stabilise a positive charge. With an amino donor group a produ ct due to Wagner-Meerwein rearrangement is formed while with a methoxy donor group Nametkin rearrangement is the preferred pathway. (C) 1997 Elsevier Science Ltd.