LAUSR

A metal-free route to PET probes Positron emission tomography (PET) is a widely used imaging technique for medical diagnostics and pharmaceutical development. As the name implies, it requires tracers that emit positrons, typically through labeling with fluorine or carbon radioisotopes. W. Chen et al. devised a versatile technique to incorporate radioactive fluoride into aromatic rings. The metal-free photochemical method directly substitutes aryl carbon-hydrogen bonds with [18F]fluoride and so is particularly well suited to late-stage transformation of complex molecules into tracers. Science, this issue p. 1170 A metal-free route to positron emission tomography tracers directly substitutes aromatic C–H bonds with radioactive fluoride. Positron emission tomography (PET) plays key roles in drug discovery and development, as well as medical imaging. However, there is a dearth of efficient and simple radiolabeling methods for aromatic C–H bonds, which limits advancements in PET radiotracer development. Here, we disclose a mild method for the fluorine-18 (18F)–fluorination of aromatic C–H bonds by an [18F]F− salt via organic photoredox catalysis under blue light illumination. This strategy was applied to the synthesis of a wide range of 18F-labeled arenes and heteroaromatics, including pharmaceutical compounds. These products can serve as diagnostic agents or provide key information about the in vivo fate of the labeled substrates, as showcased in preliminary tracer studies in mice.