Halogen-Exchange Fluorination of Aromatic Halides with HF or HF-Base

卤代卤代化合物如氯代嘧啶、卤代吡啶、氯代喹啉、2-氯苯并恶唑、2-氯苯并噻唑，或卤代化合物如2，4-二硝基氯苯，在HF或HF-碱溶液中进行卤素交换反应，以良好的产率得到相应的氟化物。该反应可以很好地解释为起始于底物中氮原子的初始质子化。然而，在HF中加入吡啶对2-氯嘧啶的卤素交换取代无效。相反，增加HF中吡啶的量显著阻碍了卤素交换产物几乎完全被底物2-氯嘧啶回收。取代的2-氯吡啶和氯喹啉的反应也引发了卤素与HF的交换反应，这些卤素存在于环中的N原子附近，以良好的产率提供相应的氟化物。

Heteroaromatic halides such as chloropyrimidines and halopyridines, chloroquinolines, 2-chlorobenzoxazole, 2-chlorobenzothiazole, or aromatic halides such as 2,4-dinitrochlorobenzene under went halogen-exchange fluorination with the treatement of HF or HF-base solutions to afford the corresponding fluorides in good yields. The reaction may be well explained to start by its initial protonation of nitrogen atom in the substrates. However, the addition of pyridine to HF was not effective for the halogen-exchange fluorination of 2-chloropyrimidine. On the contrary, increasing the amount of pyridine in HF hinders remarkably the halogen-exchange fluorination to be recovered by the substrate 2-chloropyrimidine almost exclusively. The reaction of substituted 2-chloropyridines and chloroquinolines also initiates the exchange fluorination of halogens with HF, which exist adjacent to N atom in the ring, affording the corresponding fluoride, in good yields.