Electrolytic partial fluorination of organic compounds. Part X1 Regioselective anodic monofluorination of phenylsulfenylacetate using a flow-cell system

Abstract

Organofluorine compounds have attracted much interest on account of their potential biological activity [1-3]. The synthesis of these compounds, however, is limited in many cases because of the strong electron-withdrawing ability of the fluorine atom (for example, [4]). Although direct fluorinations are the most simple way for the synthesis of such compounds, methods are not always straightforward and have to use troublesome reagents (explosive, sensitive to air or moisture, expensive) (for example, [5]). Thus, electrochemical fluorination is an ideal method for direct fluorination. Although electrochemical perfluorinations (Simons process) are familiar, electrochemical partial fluorination has been seen in few cases. In electrochemical fluorinations it is difficult to control the chemo and regioselectivity. Indeed, reported electrochemical partial fluorinations of organic compounds were not successful (low yields and product selectivity) [6-9], and there have been no reports on electrochemical partial fluorination on a large scale. Recently, the present authors [10, 11] and Laurent et al. [12] reported highly regioselective electrochemical monofluorination at c~-position to the sulfur atom of sulfides using Et3N. 3HF as a supporting electrolyte and a fluorine source. It was pointed out that this reaction proceeds by a Pummerer like mechanism via a unique fluorosulfonium cation intermediate (A) (Scheme 1) [13]. Preliminary results have shown that the anodic monofluorination could be conducted, not only in controlled potential electrolysis, but also in galvanostatic electrolysis.