Chapter one presents an account of the isolation and structure determination of thapsigargin and related natural products. Chemical manipulations of the natural product skeleton are discussed. Chapter two details the biological activity of the natural product. The structure-activity relationships are also described. Chapter three introduces the synthetic plan for thapsigargin, incorporating a Prins reaction to generate the hydroazulene skeleton of the natural product. Chapter four describes a revised synthetic strategy, based upon a ring closing metathesis reaction. Attempts to install the stereochemistry at C-10 in thapsigargin with improved selectivity are discussed. Chapter five describes the developments of a model system to study the proposed end-game in the synthesis of thapsigargin. Chapter six provides a formal account of the experimental procedures, and the appendices contain supporting information (X-ray Crystallographic data and selected NMR spectra).

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This thesis describes the synthetic studies towards dihypoestaxide, accompanied by total syntheses of aritasone and (+)-cymbodiacetal. These are all terpene derived natural products that share a common spirochroman core structure. The introduction details the isolation, biological significance and proposed biosynthesis of the aforementioned natural products, followed by a review of the previous work towards them. The key step in OUf synthesis is a heteTo-Diels-Alder dimerisation reaction of the corresponding monomeric exocyclic enane for the formation of a common tricyclic spirochroman core structure. The hetero-Diels-Alder cycloaddition reaction is reviewed. with special regard to its stereochemical outcomes, which suggest a preference for the endo-cyclOtiddition pathway in this reaction. The results and discussion section gives a detailed account of the preliminary studies undertaken to explore the hetero-Diels-Alder dimerisation. Our attempts to synthesise aritasone via the dimerisation of pinocarvone are described, which resulted in a total synthesis of aritasone and X -ray analysis confirmed the stereochemistry of the natural product.

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