New substrates for Pauson-Khand reaction
The Pauson-Khand reaction, a formal 2+2+1 cycloaddition of an alkene n bond, an alkyne n bond and carbon monoxide to form a five-membered ring, was discovered in the early 1970's. This thesis presents the work undertaken towards the synthesis of two new types of substrates for this reaction namely silicon tethered enynes and silyl enol ethers. Silicon-tethered enynes as substrates for PKR The scope of silicon-tethered Pauson-Khand reactions of vinylsilane and allylsilane derived enynes was fully explored. The vinylsilane derived enynes yielded monocyclopentenone where the carbons bound to the silicon tether were reduced during the course of the reaction. The allylsilane derived enynes yielded the desired Pauson- Khand products in good to moderate yields. A series of allylsilane derived enynes with varying substituents at both alkyne and alkene moieties were synthesised and subjected to Pauson-Khand reaction. Silyl enol ethers as substrates for PKR Pauson-Khand reactions of the TMS and TIPS enol ethers of model substrates, derived from diethyl malonate, were investigated. The methodology developed for these silyl enol ethers was then applied to the synthesis of a model substrate for ingenol. Synthesis of model substrate for Ingenol Ingenol, is a highly oxygenated tetracyclic diterpene, isolated initially from the Euphorbia ingens species of the Euphorbiaceae plant family, by the Hecker group in 1968. It has attracted considerable interest from both the chemical and biological communities because of its unique structure and an array of biological properties. Ingenol has a frYws-intrabridgehead BC ring junction. We have investigated the possibility of using the PKR to synthesise the ring skeleton of ingenol in an atom efficient and stereospecific manner.