This thesis examines the issues of acyclic stereocontrol in the Claisen rearrangement,
with particular emphasis on the effects of exopericyclic stereocentres – i.e. those
adjacent to the array of atoms directly involved in the sigmatropic process. It is
divided into three main parts:
The first section provides a review of the field of acyclic stereocontrol. The models
used to explain the development of relationships between stereocenters in systems
lacking well-defined conformational constraints are discussed. This is an established
field and particular emphasis is given to recent developments in the modelling of such
systems.
The second section discusses the results of our studies. Previous examples of
exopericyclic stereocontrol in sigmatropic rearrangements are shown. Studies are
presented that explore the importance of heteroatom-bearing stereocenters and effects
of olefin substitution pattern on the manner and extent of stereoselectivity. Our efforts
to exploit these stereochemical effects in the synthesis of small molecules are then
presented. A novel reaction sequence is presented in which equilibrating mixtures of
allylic azides undergo stereoselective Claisen rearrangements and further chemistry of
the products of this transformation is then explored. These studies, and attempts to
deploy them in synthesis allow us to draw conclusions on the nature of acyclic
stereocontrol in the Claisen rearrangement.
The third section contains experimental procedures and characterisation data for all
compounds prepared.