The Asymmetric Synthesis of Several Fragrant Natural Products

The thesis covers the synthetic routes to the jasmonoids, in particular the methyl jasmonates. It is divided into several chapters. The initial chapter covers background on the jasmonates including the discovery, occurrence in nature and the biosynthesis of these compounds along with the more recent research into their biological activity as plant pheromones. This section also focuses in more detail, using selected examples from the chemical literature, on the various syntheses to methyl dihydrojasmonates (hedione), methyl frans-jasmonates and methyl epi-jasmonates together with the problems associated with these. Chapter 2 explores synthetic routes to the trans-jasmonoids in particular methyl dihydrojasmonate. A particular emphasis is placed upon the asymmetric conjugate addition reaction, using extended enolates of homochiral phospholidinone templates (derived from homochiral ephedrine), to afford methyl frans-dihydrojasmonates (hedione) in high enantioselectivity. This asymmetric conjugate reaction is further explored in Chapter 3 where we use this synthetic asymmetric methodology is used to prepare both enantiomers of methyl frans-jasmonates proceeding via a functionalised enone system. The synthesis of the intermediates required for the conjugate additions are also presented. In Chapter 4 a novel route to racemic epi-jasmonate is discussed. The synthetic routes concentrate on a Diels-Alder strategy. It includes our initial investigations comprising, the cycloaddition reactions of 2-cyclopenten-1-one with 2-methoxybutadiene and isoprene using various Lewis acids, together with a synthetic route to a racemic mixture epi-jasmonate using concentrated solutions of lithium perchlorate to catalyse the Diels-Alder reaction of 2- cyclopenten-1-one spiroketals with isoprene. This synthetic route was developed further by using chiral spiroketals of 2-cyclopenten-1-one derived from tartaric acid, in an attempt to introduce chirality during the cycloaddition. This work also provided an insight into the mechanism of this particular cycloaddition reaction. Chapter 5 highlights the two synthetic routes to the calythrone analogue (n-butyl-3,4- dimethylcyclopent-3-en-2,3-dione). The first route is based upon the rearrangement of a derivative of 2,3-dimethylmaleic anhydride. The latter comprises the Pauson-Khand reaction to establish the functionalised cyclopentendione skeleton. Finally a formal description of the experimental results and procedures is presented