α-Fluorination of Sulfides with N-Fluoropyridinium Triflates

The reaction of sulfides possessing α-hydrogen with various N-fluoropyridinium salts was examined. While the fluorinating power increased in the order of N-fluoro-2,4,6-trimethylpyridinium triflate 1<N-fluoropyridinium triflate 2<N-fluoro-3,5-dichloropyridinium triflate 3, the yield of an α-fluoro sulfide decreased in the order of 1>2, and 3 no longer produced the α-fluoro sulfide. Triflate 1 was more reactive than the corresponding tetrafluoroborate 4. Thus, it was shown that 1 satisfactorily fluorinated various kinds of sulfides under very mild conditions, giving α-fluoro sulfides. A two-step mechanism, oxidative fluorination of sulfur and Pummerer-type rearrangement, was proposed for the fluorination. The corresponding α-fluoro sulfoxide or sulfones were easily prepared from the sulfides by successive fluorination–oxidation procedure.