Application Progress of N-Heterocyclic Carbene-mediated Concerted Nucleophilic Aromatic Substitution in ¹⁸F Labeling Reaction

Concerted nucleophilic aromatic (CS_NAr) substitution reactions play an important role in nuclear chemistry synthesis, and are now used to develop positron radiotracers. Compared with the traditional nucleophilic aromatic substitution reaction, the advantages of this substitution reaction lie in the fact that the range of substrates is not limited to electron-deficient aromatic compounds, and the radiolabeled products can be easily separated from the reaction system. In this paper, the mechanism of concerted nucleophilic aromatic substitution reaction was first elaborated, and the CS_NAr reaction mediated by 1,3-bis(2,6-diisopropylphenyl)2-chloroimidazolium chloride(SIPr·HCl) and its application progress in the preparation of positron nuclide-labeled radiotracer were focused. We emphasized the importance of concerted nucleophilic aromatic substitution reactions for synthesizing ¹⁸F radiotracers, summarized existing shortcomings, and prospectd future application prospects.