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Photocatalytic C(sp³)–C(sp²) radical-polar crossover cross-coupling of styrenyl boronic acids
|Watson, Allan John Bell
|Organoboron reagents are widely used in organic chemistry due to their versatile reactivity, ubiquity, stability, and low cost. They are commonly employed as coupling partners in cross-coupling reactions, such as the Pd-catalysed Suzuki-Miyaura reaction, which is responsible for 40% of C–C bond formation reactions in the pharmaceutical industry. However, with the development of the photoredox chemistry over the last 15 years, radical-mediated cross-coupling reactions have flourished. Radicals are now easily made from cheap-commercially-available or easy-to-make precursors using visible light irradiation. They can then further react with numerous different coupling partners leading to an extensive range of new cross coupling opportunities, without the requirement for a photocatalyst in some cases. Organoborons have mostly been employed as radical precursors but their use as coupling partners has increased over the past few years. N-(Acyloxy)phthalimides (NHPI) esters, a class of redox activated ester species, are widely used as alkyl radical precursors owing to their bench-stability and ease of access. Single electron transfer (SET) affords the desired radical through decarboxylation. In this work, we disclose a new method for C–C bond formation between a styrenyl boronic acid and NHPI ester under Ru-mediated photocatalysis. The reaction proceeds smoothly within three hours under blue LED irradiation and affords the desired products in good to excellent yields. The radical addition undergoes unusual polarity-mismatched Giese-type addition to the organoboron coupling partner. A radical polar crossover reaction requires the presence of a redox-active additive to enable the desired bond formation to occur, and proceeds via an unusual boronic acid priming event. This thesis will describe the development and application of this reaction.
|Photocatalytic C(sp3)–C(sp2) radical-polar crossover cross-coupling of styrenyl boronic acids (thesis data) Brals, J., University of St Andrews, 30 Oct 2023. DOI: https://doi.org/10.17630/66a59db2-4d79-4457-b019-b99bfa9c0eff
|Photocatalytic C(sp³)–C(sp²) radical-polar crossover cross-coupling of styrenyl boronic acids
|PhD Doctor of Philosophy
|The University of St Andrews
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