Photoinduced Generation of Electrophilic Radicals: N-Arylation, N-Cyclisation and Vinylation Reactions

UoM administered thesis: Phd

  • Authors:
  • Daniel Fernández Reina

Abstract

Radicals are a powerful class of reactive intermediates that can be used in a wide variety of synthetic transformations. Classical generation of radicals usually involves the use of highly toxic and reactive radical initiators (like tin species) and harsh reaction conditions. This has resulted in a limited functional group compatibility in radical chemistry. The appearance of visible light-mediated photoredox catalysis has contributed to the generation of radicals under milder conditions and renewed the interest in radical chemistry. In this thesis, visible light-mediated photoredox catalysis has been applied towards the generation of electrophilic radicals and their use in addition reactions. Initial work used O-aryloxyamides as suitable NCR precursors. These bench-stable precursors are easily synthesised from commercially available reagents and deliver amidyl radicals upon a single-electron reduction, using organic dye Eosin Y as the photocatalyst. This strategy for NCR generation was successfully applied in the intermolecular amidation of a variety of arenes. O-aryloxyamide precursors bearing a pendant alkyne were used in the development of the first radical N-5-exo-dig cyclisation. This time, control experiments showed that the reaction did not require the use of a photocatalyst, however, continuous visible light irradiation was necessary for the reaction. Finally, alkyl bromides were used as precursors of CCRs and used in the intermolecular vinylation reaction upon addition to vinyl trifluoroborates. This reaction proceeded under visible light irradiation using, again, organic photocatalyst Eosin Y. The ipso substitution that takes place upon addition to vinyl trifluoroborates can be regarded as a formal visible-light mediated transition-metal free Suzuki cross-coupling and was successfully utilised in the late-stage olefination of biologically active molecules.

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Original languageEnglish
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Award date1 Aug 2019