A protocol for controlled reactivity shift in the 2,2-difluorovinyl motif used for selective S-18F and C-18F bond formation.

Positron emission tomography (PET) is a powerful imaging technique for biomedical research, drug development and medical diagnosis. The power of PET lies in biochemically selective radiotracers, labelled with positron emitters like fluorine-18 image chemical processes in vivo. A rapid and remarkably efficient, unprecedented protocol to select between S-F and C-F bond formation based on activation of 1,1-difluoroethylene groups followed by selective oxidation or reduction is described. While transition metal mediated conditions can be employed, the reaction proceeds in high yield using unobjectionable chemical reagents amenable to routine radiotracer production. The latter bodes well for facile clinical translation of the method. The new technique affords radiotracers and the labelling reagent 2,2-difluoro-2-(fluoro-18F)ethyl 4-methylbenzenesulfonate ([18F]1b) in excellent yield. Following oxygenation of the reaction mixture with medical oxygen or air, sulfonyl fluorides are obtained as the primary product. The new protocol was employed in a proof of principle to develop a radiometric assay for quantitation of sulfonylation yield with sulfonyl fluoride reagents. With operational ease and mild conditions, the method bodes a high potential for radiolabelling of biomolecules, known enzyme inhibitors and other temperature-sensitive compounds.

Transition metal free, late-stage, regiospecific, aromatic fluorination on a preparative scale using a KF/crypt-222 complex.

We herein report the development of a convenient, regioselective, aromatic fluorination method of hypervalent iodonium ylides for synthesising fluoro-arenes on a preparative scale. This transition metal free, nucleophilic methodology provides good yields for sterically hindered substrates, irrespective of activation. The methodology simplifies reference synthesis for PET imaging.

Organocatalyst-assisted Ar-18F bond formation: a universal procedure for direct aromatic radiofluorination.

A metal free, phosphane-catalysed protocol for C-F bond formation based on ipso-elimination of iodanes is described. The reaction proceeds in significantly higher yield and with markedly reduced variability of yields (yield range) than previously described procedures. Rapid and efficient radiofluorination is achieved using unobjectionable chemical reagents with precedence in routine radiotracer production. With operational ease and mild conditions, the method promises a high potential for radiolabelling of biomolecules.