This review summarizes the applications of iodonium compounds in the rapidly developing field of Positron Emission Tomography (PET). Reactions of diaryliodonium salts with fluoride anion have found wide practical application in PET as a fast and convenient method for the introduction of the radioactive [18 F]-fluoride into radiotracer molecules. The best synthetic methods for the preparation of iodonium precursors for PET are described, the mechanistic aspects of nucleophilic fluorination reaction are discussed, and specific examples of the preparation of PET radioligands are provided.

New powerful hypervalent iodine(V) oxidants, tosylate and mesylate derivatives of 2-iodoxybenzoic acid (IBX), were prepared by the reaction of IBX with the corresponding sulfonic acids. Single crystal X-ray crystallography of the diacetate derivative of IBX-tosylate revealed an unusual heptacoordinated iodine geometry without any significant intermolecular secondary interactions.

(4-Triisopropylsilylphenyl)phenyliodonium tosylate, an aryliodonium salt bearing an extremely bulky, electron-donating triisopropylsilyl (TIPS) substituent in the phenyl ring, was prepared by the reaction of (4-tributyltinphenyl)triisopropylsilane with [hydroxy(tosyloxy)iodo]benzene (Koser's reagent). The TIPS-substituted aryliodonium tosylate was further converted into (4-triisopropylsilylphenyl)phenyliodonium bromide, the structure of which was established by sin-

New hypervalent iodine(V) oxidants are prepared by the reaction of IBX with sulfonic acids.