Nucleophilic aromatic substitution (S N Ar) is a classical reaction with well-known reactivity toward electron-poor fluoroarenes. However, electron-neutral and electron-rich fluoro(hetero)arenes are considerably underrepresented. Herein, we present a method for the nucleophilic defluorination of unactivated fluoroarenes enabled by cation radical-accelerated nucleophilic aromatic substitution. The use of organic photoredox catalysis renders this method operationally simple under mild conditions and is amenable to various nucleophile classes, including azoles, amines, and carboxylic acids. Select fluorinated heterocycles can be functionalized using this method. In addition, the late-stage functionalization of pharmaceuticals is also presented. Computational studies demonstrate that the site selectivity of the reaction is dictated by arene electronics.

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Positron emission tomography (PET) is a powerful imaging technology that could visualize and measure metabolic processes in vivo and/or obtain unique information about drug candidates at early stages. Identi cation of new and improved molecular probes plays a critical role in PET, but its progress is limited in many situations due to the lack of e cient and simple labeling methods to modify biologically active small molecules and/or drugs. Although various approaches have been reported, current methods to radio uorinate unactivated arenes are still limited. Here we document the discovery of a robust method for constructing C-18F bonds through direct halide/18F conversion in electron-rich halo(hetero)arene substrates. Based on readily available halide precursors and mild photoredox conditions, [18F]F-is e ciently introduced into a broad spectrum of organic molecules, including pharmaceutical compounds in a site-selective manner. Notably, the direct 19F/18F conversion method is demonstrated to be a simple and robust protocol for PET probe screening/preparation: this methodology not only identi es a new cancer imaging agent L-61-18F-COOH after a rapid screening of a tyrosine isomer library; but also allows the simple and high-yielding synthesis of the widely used PET agent L-[18F]FDOPA. Taken together, photoredox-mediated halide/18F interconversion strategies represent an innovative chemical tool to prepare new and clinically signi cant PET agents that are synthetically inaccessible or cumbersome to achieve by traditional methods.

An operationally simple, robust, metal-free approach to the synthesis of N-acyl azoles from both alcohols and aldehydes is described. Oxidative amidation is facilitated by a commercially available organic oxidant (4-acetamido-2,2,6,6-tetramethylpiperidine-1-oxoammonium tetrafluoroborate) and proceeds under very mild conditions for an array of structurally diverse substrates. Tandem reactions of these activated amides, such as transamidation and esterification, enable further elaboration. Also, the spent oxidant can be recovered and used to regenerate the oxoammonium salt.

A mechanistic investigation into the amination of electron-neutral and electron-rich arenes using organic photoredox catalysis is presented. Kinetic and computational data support rate-limiting nucleophilic addition into an arene cation radical using both azole and primary amine nucleophiles. This finding is consistent with both fluoride and alkoxide nucleofuges, supporting a unified mechanistic picture using cation radical accelerated nucleophilic aromatic substitution (CRA-SNAr). Electrochemistry and time-resolved fluorescence spectroscopy confirm the key role solvents play in enabling selective arene oxidation in the presence of amines. The synthetic limitations of xanthylium salts are elucidated via photophysical studies. An alternative catalyst scaffold with improved turnover numbers is presented.