19F- and 18F-arene deoxyfluorination via organic photoredox-catalysed polarity-reversed nucleophilic aromatic substitution

Nucleophilic aromatic substitution (SNAr) is routinely used to install 19F– and 18F– in aromatic molecules, but is typically limited to electron-deficient arenes due to kinetic barriers associated with C–F bond formation. Here we demonstrate that a polarity-reversed photoredox-catalysed arene deoxyfluorination that operates via cation-radical-accelerated SNAr enables the fluorination of electron-rich arenes with 19F– and 18F– under mild conditions, and thus complements the traditional arene polarity requirements necessary for SNAr-based fluorination. The utility of our radiofluorination strategy is highlighted by short reaction times, compatibility with multiple nucleofuges and high radiofluorination yields, especially that of an important cancer positron emission tomography agent [18F]5-fluorouracil. Taken together, our fluorination approach enables the development of fluorinated and radiofluorinated compounds that can be difficult to access by classical SNAr strategies, with the potential for use in the synthesis and discovery of positron emission tomography radiopharmaceuticals. Site-selective installation of fluorine (19F) and its radioisotope (18F) in aromatic molecules can lead to high-value products, but methods for this purpose are not without limitations. Now, using photochemistry, a 19F- and 18F- labelling strategy is reported that complements traditional approaches.