Rapid and Efficient Radiosyntheses of meta-Substituted [18F]Fluoroarenes from [18F]Fluoride Ion and Diaryliodonium Tosylates within a Microreactor

Effective methods for the introduction of the short-lived positron-emitter fluorine-18 (t(1/2) = 109.7 min) at high specific radioactivity into fluoroarenes are valuable for the development of radiotracers for molecular imaging with positron emission tomography. We have explored the scope of the radiofluorination of diaryliodonium salts with no-carrier-added (NCA) [F-18]fluoride ion for the preparation of otherwise difficult to access meta-substituted [F-18] fluoroarenes. A microfluidic reaction platform was used to establish optimal radiochemical yields. Rapid, high yielding and selective radiofluorinations were achieved in unsymmetrical diaryliodonium to-sylates (ArI+Ar'TsO-), in which Ar carried either a meta electron-withdrawing (CN, NO2, CF3) or electron-donating (Me or MeO) group, and in which the partner aryl group (Ar') was relatively electron-rich, such as Ph, 3-MeC6H4, 4-Me-OC6H4, 2-thienyl, or 5-Me-2-thienyl. The radiofluorination of appropriate diaryliodonium tosylates is therefore a generally useful method for the preparation of simple [F-18]m-fluoroarenes ([F-18]ArF).