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Regioselective anodic monofluorination of aryl 2,2,2-trifluoroethyl sulfides gave, exclusively, aryl 1,2,2,2tetrafluoroethyl sulfides, the products of fluorination at the position « to the trifluoromethyl group. The a-monofluorination of sulfides bearing electron-withdrawing substituents other than trifluoromethyl was also successful. Furthermore, the procedure could be applied to the «,«-

Highly regioselective anodic monofluorination of various aryl and alkyl fluoroalkyl sulfides was successfully carried out, and fluorine was exclusively (aryl sulfides) or preferentially (alkyl sulfides) introduced at the position a to the fluoroalkyl group. Even simple alkyl phenyl sulfides devoid of an electron-withdrawing group could be anodically monofluorinated in satisfactory yields for the first time when etheral solvents were used as an electrolytic solution. A unique Pummerer-type mechanism via fluorosulfonium ions was proposed for this anodic fluorination by comparison with anodic -methoxylation previously studied.

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A unique Pummerer type mechanism via fluorosulphonium ions for anodic monofluorination of sulphides is established by comparing the anodic monofluorination of partially halogenated ethyl phenyl sulphides (1, PhSCH2R; R = CF3, CF2H, CFH2, CF2CI, CCIH2) with their anodic methoxylation; simple alkyl phenyl sulphides 2 bearing no electron-withdrawing group could be monofluorinated anodically in satisfactory yields for the first time when tetrahydrofuran was used as a solvent.