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

在HF或HF碱溶液中进行卤素交换氟化，得到相应的高收率氟化物，如氯嘧啶和卤代吡啶、氯喹啉、2-氯苯并恶唑、2-氯苯并噻唑等杂芳烃卤化物或2,4-二硝基氯苯等芳烃卤化物。这个反应可以用底物中氮原子的初始质子化来解释。然而，吡啶与HF的加成对2-氯嘧啶的卤素交换氟化效果不明显。相反，增加HF中吡啶的量会明显阻碍底物2-氯嘧啶几乎完全回收卤素交换氟化。取代的2-氯吡啶与氯喹啉的反应还引发卤素与HF的交换氟化，HF存在于环中N原子附近，提供相应的氟，产率高。

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.