Photochemical Initiation and Reactions of Thiyl Radicals Studied with SH2’ Radical Traps

Peter J.H. Williams, Hon Eong Ho, William P. Unsworth, Andrew R. Rickard, Victor Chechik*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

A radical trapping method based on an SH2’ homolytic substitution reaction was applied to study the mechanism of a photochemical spirocyclisation of indole-ynones in the presence of thiols. Starting material, products and a range of trapped radical intermediates were simultaneously detected in reaction mixtures by mass spectrometry (MS). The trapped intermediates included both initiating and main chain propagating radicals. These data made it possible to propose a self-initiation mechanism consistent with the originally postulated photoexcitation of an intramolecular electron donor-acceptor complex of the substrate. The effect of thiol structure on the MS peak intensity of the reaction components was rationalised in terms of the relative stability of the radical intermediates. The results were compared to a simpler related reaction, a photochemical thiol-ene addition where reagents, products and trapped intermediate radicals were also detected by MS. Relative MS peak intensities were again explained by a combination of electronic and steric effects on the stability of intermediate radicals. Overall, SH2’ radical trapping was demonstrated to be a powerful experimental technique for providing mechanistic evidence on photochemical and other organic radical reactions.

Original languageEnglish
Article numbere202401500
Number of pages8
JournalChemistry - A European Journal
Early online date23 Aug 2024
DOIs
Publication statusE-pub ahead of print - 23 Aug 2024

Bibliographical note

Publisher Copyright:
© 2024 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.

Keywords

  • Photochemistry
  • Radical reactions
  • Radical trapping
  • Radicals
  • Reaction mechanisms

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