4- fluoro- sulfane

Carboxylic and sulfonic acids e. g. 1 and 3, are smoothly converted under mild conditions to their corresponding fluorides, e.g. 2 and 4 respectively by treatment with (dialkylamino)tri-fluoro-x4-sulfanes. 

Sulfane Bis-f4-fluoro-N-trifluoro-mcthyl-anilino]- ElOa. 258 (RN = C —S I IF,)... 

DAST (1) and the related aminofluoro-/ -sulfanes convert primary, secondary, tertiary, allylic and benzylic alcohols into fluorides under mild conditions in high yield with little byproduct formation. In this respect they are superior to most other fluorinating agents. DAST (1) and other aminofluoro-2 -sulfanes can fluorinatc hydroxy acids and hydroxy ketones selectively to give the corresponding fluoro acids and fluoro ketones, which is impossible or, at least, diflicult w ith sulfur tetrafluoride. 

Fluoro-A -sulfanes, such as sulfur tetrafluoride, diethylaminosulfur trifluoride (DAST) ° and piperidinosulfiir trifluoride,are able to selectively substitute the trimethyl-siloxy group by fluorine under mild conditions. 

The conversion of silyl ethers into fluorides may serve as an indirect method for the conversion of hydroxy compounds into fluorides, but in some cases the silyl ethers are not formed from the corresponding alcohols and then a step is saved by direct conversion into the fluorides. Two classes of fluorinating reagents have been used so far to transform silyl ethers into fluorides these are fluoro-2 -phosphanes, which were used first, and fluoro-24-sulfanes. 

The next logical step was the extension of this chemistry to SH derivatives. Attempts to oxidatively fluorinate CF3SSH with monofluoroxenonium hexafluorometalates failed, even at 195 K. Only decomposition into the already mentioned Sg + salts could be observed (24). On the other hand, the synthesis of the fluoro(trifluoromethyl)sulfonium- and fluoro(methyl)sulfonium cations from the SH acidic sulfanes CF3SH and CH3SH proceeded without difficulty at 213 K (Figure 1) (25). The elimination of HF at 213 K is expected to be preferred from a thermodynamic point of view, although HF elimination is probably kinetically inhibited in this case. However, at 233 K decomposition of all of these compoimds into the characteristic blue Sg2+ salts is observed. By reaction with chlorine... 

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