Cuthbertson, J; (2016) Potassium Alkoxides and Thiolates in Transition Metal-Free Synthesis: Mechanism and Application. Doctoral thesis , UCL (University College London).

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Abstract

One of the most significant developments in chemistry over the last forty years has been the ability to harness and exploit the reactivity of low-valent transition metals, especially palladium. A bewildering array of metal and ligand combinations have allowed a similar number of previously unprecedented transformations to become routine; so much so, that transformations such as the Heck, Sonogashira, Suzuki and Stille reactions have become a mainstay of the organic chemist’s toolbox. However, the sometimes prohibitive cost of transition metals and ligands, their inherent toxicity and laborious clean up procedures have directed attention towards approaches that bypass the need for transition-metal catalysts. Recently, a number of publications have indicated that reactions previously thought to be unique to transition metal catalysis could instead occur in the presence of a strong base and a non-metal additive. However, there remains significant controversy regarding the mode of reactivity. This thesis presents evidence to suggest that, under carefully controlled conditions, potassium alkoxides and thiolates have an inherent electron transfer ability. Mechanistic work is presented to suggest that an understanding of this mode of reactivity allows access to a number of substrates and reactions that have previously been considered the preserve of transition metal catalysis, including biaryl formation and sp-displacement reactions. In addition, an appreciation of the mode of reactivity of potassium alkoxides has allowed a mechanistic reevaluation of common transformations, such as the synthesis of enol ethers from terminal alkynes. With a solid understanding of the underlying reaction mechanism, the reducing behaviour of cheap and readily available alkoxides or their sulfur analogues could subsequently be applied to the attempted synthesis of chemical scaffolds that are common in many natural products.

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