Pyridine, anodic fluorination

Erian, A.W., Konno, A., and Euchigami, T., Electrolytic partial fluorination of organic compounds. Part 19. A novel synthesis of fluorothieno[2,3-h]pyridines using anodic fluorination of heterocyclic sulfides as a key step, J. Org. Chem., 60, 7654, 1995. 

Anodic fluorination of pyridine in EtsN 3HF gives 2-fluoropyridine in 22% yield (85EA1075). Because the heterocyclic ring contains electron-accepting substituents. 

Pyridines with an SCH2R group in the a position also undergo anodic fluorination, forming monofluoro derivatives (94TL7245) (Scheme 44). 

Owing to the presence of a CN group in the jS position (2-pyridyl sulfide 28), anodic fluorination in the presence of a base yields a bicyclic heterocycle (2-fluor-othieno[2,3-Z2]pyridine 30). Perhaps, the first step of the reaction is anodic mono-fluorination of 2-pyridyl sulfide to a fluoromethyl-pyridyl sulfide. In basic media, the... 

Anodic regioselective fluorination of a-phenylsulphenylated ethyl acetates, 1-naphthalene and 2-pyridine derivatives [80], l-aryl-3-(phenylthio)oxindoles and 2-substituted-3-oxo-4-(phenylthio)-l, 2, 3,4-tetrahydroisoquinolines [81], 2-benzo-thiazolyl and 5-chloro-2-benzothiazolyl sulfides [82], a-(phenylsulfenyl)lactams [83], as well as various heterocycles such as thiolanones, oxathiolanones, dithi-olanones, 3Fl-l,4-benzoxathian-2-ones [84] in Et3N-3HF or Etr NF- HF [n = 3,4), has been reported. 

It was demonstrated that 4-fluoropyridine can be synthesized by electrochemical fluorination of pyridine on the platinum anode at constant voltage in acetonitrile solution containing Et3N-3HF as supporting electrolytes and fluorine sources. ... 

Solvent-free electrochemical fluorination is an alternative method for preventing anode passivation and acetoamidation [18, 19]. As already mentioned, handling extremely corrosive and poisonous anhydrous HF in a laboratory setting is accompanied by serious hazards and experimental difficulties. Molten salts such as 70 % HF/pyridine (Olah s reagent) and commercially available EtaN-SHF [20] are often used to replace anhydrous HF. Other molten salts with the general formula R4NF-nHF (n > 3.5, R = Me, Et, and n-Pr) are useful in selective electrochemical fluorination. These electrolytes... 

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