Synthesis of Biphenyl Iodonium Salts as (Radio)labelling Precursors for Fluoroarenes

Radiolabelled [ 18 F]fluorobiphenyl moieties are often used for the development of positron emission tomography (PET) tracers in several medicinal fields, including tumor detection, epilepsy, and Alzheimer's disease.Since these electron-rich [ 18 F]fluoroarenes cannot be obtained through traditional SNAr reactions, other radiolabelling precursors are required.For example, [ 18 F]fluorobiphenyl moieties can be obtained from (biphenyl)(aryl)iodonium salts.These biphenyl iodonium salts are often synthesized from iodobiphenyls or biphenylboronic acids.However, these syntheses require harsh reaction conditions, limiting the scope for oxidation and acid-sensitive biphenyls.As a potential solution, we attempted to synthesize biphenyl iodonium salts from biphenyl and pre-oxidized iodoarenes.However, this approach was found to be unsuccessful.Instead, easily obtained biphenyltrimethylsilanes were found as a promising starting point for the synthesis of biphenyl iodonium salts under mild conditions.The synthesized diaryliodonium salts were successfully used for fluorination reactions, indicating the potential of these precursors in the synthesis of fluoroarenes.