Some novel aspects of carbocation chemistry via Sn1 ring opening of epoxides
This thesis concentrates on the study of the SnI like ring opening of epoxides, and in particular, it focuses on the formation of ally lie alcohols and a,/-unsaturated ketones from epoxides. The work is described in the three main chapters of this thesis. An introductory chapter reviews the target natural product, I-carvone, and its industrial applications. There is a comprehensive review of the existing preparative methods of allylic alcohols from epoxides, with detailed discussion of the types of mechanisms involved. Subsequently, there is a discussion on the transformation of epoxides to ,/-unsaturated ketones. The chapter covering results and discussion opens with a brief overview of the investigational work previously carried out into the SnI like ring opening of a model molecule, 1-methylcyclohexene oxide. This is followed by a description of how a new methodology for the acidic ring opening of epoxides was developed and optimised. This chemistry, leading to the formation of allylic alcohols through an SnI like mechanism, involved the use of a urea derivative. The scope and limitations of this novel methodology are then discussed through its application to a wider range of epoxide substrates. The chapter elaborates on the different strategies attempted, based on some adaptation of some of the existing methods of oxidation of alcohols to ketones, to achieve a one-pot synthesis of an a,/-unsaturated ketones from an epoxide. A novel synthesis was subsequently developed using a triflate sulfonium salt. The chapter is rounded off with a summary of the results of this work and of prospective future work. A concluding chapter provides a formal description of the experimental results and procedures together with appropriate references.