| Summary: | Initial discussion centres on the importance of metal-free chemistry and organosilicon chemistry and its application to reductive processes. Silicon’s uses, bonding and activation is also considered in more detail.
Chapter One discusses development of a reductive amination process using carboxylic acids as the electrophiles. Most reductive amination processes using carboxylic acids require transition metal activation, which causes selectivity and handling issues. However, Brønsted acids, specifically benzenesulfonic acid, with phenylsilane are shown to be effective, practical and chemoselective reducing agents. A range of amine substrates are synthesised, demonstrating potentially reducible functional groups, pharmaceuticals and large-scale synthesis. The reaction mechanism is also explored and shown to proceed via highly substituted silyl sulfonates upon the elimination of benzene from the silane. Computational calculations confirm increased reactivity over lower substituted sulfonates and the parent silane.
Chapter Two focusses on using the acid/silane reduction system for the methylation of amines using formic acid. Synthesis of tertiary amines, both through mono and di-methylation are demonstrated, along with complex compounds and pharmaceutical targets. The mechanism is shown to proceed via formaldehyde formed by the breakdown of the amide intermediate.
Chapter Three builds on the utility of this reductive system and investigates the reduction of phosphine oxides to phosphines, which are important for a range of processes. Reduction was shown to proceed at room temperature and a range of phosphine products are synthesised. Initial investigations are also made towards a catalytic Wittig reaction using this reduction system, and a proof of concept is demonstrated. Mechanistic studies are also undertaken, demonstrating that the reaction proceeds through formation of silyl sulfonates and subsequent interaction with the phosphine oxide.
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