The electrophilic halogenation of arenes is perhaps the simplest method to prepare aryl halides, which are important structural motifs in agrochemicals, materials, and pharmaceuticals. However, the nucleophilicity of arenes is weakened by the electron-withdrawing substituents, whose electrophilic halogenation reactions usually require harsh conditions and lead to limited substrate scopes and applications. Therefore, the halogenation of arenes containing electron-withdrawing groups (EWGs) and complex bioactive compounds under mild conditions has been a long-standing challenge. Herein, we describe Brønsted acid-catalyzed halogenation of arenes with electron-withdrawing substituents under mild conditions, providing an efficient protocol for aryl halides. The hydrogen bonding of Brønsted acid with the protic solvent 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) enables this transformation and thus solves this long-standing problem.
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