Electrochemical fluorination of heterocyclic compounds

Furin, G.G. Fluorine-containing heterocycles. Part. IV. Electrochemical fluorination of heterocyclic compounds. Adv. Heterocycl. Chem. 2006, 90, 239-310. 

Fluorine-containing Heterocycles. Part IV. Electrochemical Fluorination of Heterocyclic Compounds... 

The products of the electrochemical perfluorination of aromatic and heteroaromatic compounds are the corresponding perfluorinated cyclic and heterocyclic alkanes.28 and also per-fluorinated derivatives of the heteroaromatic compounds. Perfluorocyclohexane is the principal product from the electrochemical fluorination of benzene and fluorobenzene. Chloro derivatives of perfluorocyclohexane are produced from chlorobenzenes. Anisoles give fully saturated per-fluoro ethers, together with cleavage products. Extensive cleavage is observed in the fluorination of benzenethiols. Chloropyridines, fluorocarbons and sulfur hexafluoride or nitrogen trifluoride are characteristic byproducts from the above scries of reactions. 

Konno A, Naito W, Fuchigami T (1992) Electrolytic partial fluorination of organic compounds. 6. Highly regioselective electrochemical monofluorination of aliphatic nitrogen-containing heterocycles. Tetrahedron Lett 33 7017-7020... 

Scheme 7 Electrochemical fluorination of sulfur-containing heterocyclic compounds...

Simons process — Electrochemical polyfluorination reactions of organic compounds are the only efficient way to industrial production of perfluorinated compounds. The reaction proceeds in the solution of KF in liquid HF (b.p. 19.5 °C), where the starting substances as alcohols, amines, ethers, esters, aliphatic hydrocarbons and halo-hydrocarbons, aromatic and heterocyclic compounds, sulfo- or carboxylic acids are dissolved. During anodic oxidation, splitting of the C-H bonds and saturation of the C=C bonds occur and fluorine atoms are introduced. 

Within a potential range where radicals (like CF ) are not readily reduced or/and using indirect formation in solution by means of electron carrier, a chemistry—rather similar to that already developed by the Kolbe method by oxidation of CF3COO at a platninum anode—can be developed. Thus, Medebielle [193] showed that radical additional onto electron-rich olefins was possible and applied this for convenient synthesis of fluorinated heterocyclic compounds. Let us stress that the electrochemical process is in this case stoichiometric in electrons. 

Mazalov, S.A. Gerasimov, S.I. Sokolov, S.V. Zolotavin, V.L. Methods of preparation and properties of organic fluorine compounds. I. The electrochemical method of preparation of perfluoro tertiary heterocyclic amines. Zh. Obshch. Khim. 1965, 35(3), 485 89. 

It should be pointed out that synthesis of perfluorinated sulfur(II)-containing heterocycles, requires a custom synthetic approach, since of these compounds cannot be prepared using oxidative methods, such as electrochemical fluorination or fluorination using elemental fluorine, due to ability of divalent sulfur to undergo oxidation. 

Section IV analyzes methods of fluorine introduction in organic molecules by discussing the ECF method in order to overview and rationalize the available material on syntheses and applications of fluorinated heterocyclic compounds based on modern knowledge in this field. Is it possible for modified electrochemical techniques to produce a pronounced effect when applied on a large-scale basis Is there any opportunity to reject the old expensive and unsafe procedures for the production of fluorinated materials based on heterocyclic frameworks and to replace them by more economical, safe, and ecologically clean procedures These issues are examined in Section IV. 

---