C–H functionalisation offers a direct and atom-economical approach to modifying organic molecules, eliminating the need for prefunctionalised starting materials. Traditional benzylic C–H functionalisation methods such as, halogenation, arylation, acylation or oxidations often require harsh conditions and transition metal catalysts. In contrast, photochemical strategies utilise light to enable milder and more selective transformations. Photoredox catalysis and radical-mediated pathways have emerged as powerful tools in this area, often employing organic dyes as catalysts, thereby reducing reliance on less sustainable transition metals. Despite considerable progress, the functionalisation of electron-deficient substrates remains a challenge due to their high oxidation potentials, which lie beyond the scope of many conventional oxidants. This thesis investigates photochemical approaches to C–H functionalisation, with the goal of oxidising substrates that are typically inaccessible through ground-state oxidative methods. By employing alternative activation strategies such as photochemistry or photoelectrochemistry, oxidative catalysts can be excited or electrochemically tuned to engage substrates with oxidation potentials higher than those accessible under non-light mediated conditions. This thesis presents two projects that explore oxidative strategies for substrates that have traditionally resisted functionalisation or cross-coupling using established methods. The first project utilises the elevated oxidation potential of photoexcited 2,3-dichloro-5,6-dicyano-1,4benzoquinone (DDQ, 1) to achieve the C(sp³)–H functionalisation of electron-deficient primary and secondary benzylic substrates. The proposed mechanism proceeds via generating a reactive intermediate where the reduced form of DDQ is installed at the benzylic position forming a benzylic quinol ether bond that can be displaced by halogens, for example, to enable value-added functionalisation. The second project focuses on the design of a new class of electronically primed photoredox catalysts, developed to facilitate transformations beyond the scope of conventional photocatalysts. Alongside this project, a range of lab equipment was designed to aid this challenging area of chemistry by standardising key reaction parameters in a format that could be easily repeated by other academic teams.
Photochemical C(sp3)-H Functionalisation
Smith, C. A. (Author). 25 Sept 2025
Student thesis: Doctoral Thesis › Doctor of Philosophy (PhD)