Reductive σ-bond cleavages of challenging substrates under metal-free, mild conditions have recently been achieved with photoactivated super-electron donor (SED). These include (but are not limited to) C-O bonds of benzylic ethers and esters, C-N bonds of benzylic sulfonamides and aromatic amides. This work has successfully widened the substrate scope of reduction by SED to include i) the C-O bond cleavages of phenolic esters and aryl ethers and ii) the C-S bond cleavages of aromatic sulfides, sulfoxides and sulfones. Previously it was also discovered that the X-N bond of several amides were reductively cleaved via intramolecular electron-shuttling instead of the more conventional through-bond electron transfer. This mode of reduction by SED is not well-explored. To this end, several ester and amide-based substrates were synthesised in an attempt to expand the scope of this electron-shuttling mechanism induced by SED. This study has also been successful, with the electron-shuttling effect thought to be responsible for the C-C bond cleavage of 14 [illustration not shown], resulting in the production of 15 [illustration not shown]. Perhaps the most powerful reducing agent in the synthetic industry is the "solvated electron" which is conveniently prepared during the Birch reduction. In this work, the Birch reduction conditions were successfuly applied, in an unprecedented way, to the C-S bond cleavage of methyl-coenzyme M (MeCoM). The experimental results have the potential to contribute significantly towards our current understanding of MeCoM reductase activity. This study has also highlighted the complex nature of the Birch reduction; by simply switching from sodium to lithium, reactivity and regioselectivity could be significantly altered. Presently, some details of the mechanism for the observed reduction(s) remain unsolved.
|Date of Award||7 Jan 2016|
- University Of Strathclyde
|Supervisor||John Murphy (Supervisor) & Craig Jamieson (Supervisor)|