Fluoro-Pummerer rearrangements

Reaction of thioethers with one equivalent of NF-reagent results in the formation of a-fluorothioethers via a fluoro-Pummerer rearrangement [199] (Scheme 2.90). With appropriate excesses a-fluorosulfoxides and sulfones are obtained [200]. The thiophenyl group can also be used as a subsequently removable directing function for site-selective fluorination of natural products [201]. 

Sulfides and l,l,l-tris(methylthio)alkanes behave slightly differently. Fluoro-Pummerer rearrangement of sulfides leads to a-fluoro sulfides, whereas partial replacement of the SMe groups with fluorine atoms and concomitant a-bromination seems to be the option for the orthothioesters. ... 

The difluoroiodotoluene is an elfective reagent for the fluorination of a-phenelsul-fanyl lactones 95. The reaction involves fluoro-Pummerer rearrangment. A sequence involving conversion of a-fluorosulfide 95 into sulfoxide and elimination step was used for the synthesis of 3-fluoro-2(5H) furanones 96. ... 

A review of the scope and limitations of fluoro-Pummerer rearrangements, oxidative desulfiirization-fluorination, and oxidative desulfurization-di- and tri-fluorination reactions for the synthesis of fluorinated compounds has been reported. ... 

The same sequence of diastereoselective reduction of a /i-oxo-y-fluoro sulfoxide followed by Pummerer rearrangement and hydrolysis to the aldehyde has been used successfully in the synthesis of fluorine-containing carbohydrates.10... 

The cyclization of the Pummerer rearrangement product 30 derived from o-methylsulfinyl-difluorostyrene 29 leads to 2-fluorobenzo[ ]thiophene 31 (Scheme 7) <1997CC1537>. Treatment of thiol 32 with NaH affords 2-fluoro-4,5-dihydrothiophene 33 by a cyclization <2000CC1887>. 

Sulfides are selectively fluorinated a to the sulfur atom via a reaction similar to the Pummerer rearrangement (Table 2). The fluorination wa.s originally achieved by the direct fluorination of sulfides with xenon difluoride.This reaction is proposed to occur by initial oxidative fluorination of the sulfide to give an unstable sulfur(IV) difluoride of type 1, followed by loss of hydrogen fluoride to give intermediate 2, followed by fluorine transfer to give the a-fluoro sulfide. This fluorination has also been achieved with diethylaminosulfur trifluoride (DAST) in the absence or presence of catalytic amounts of antimony(III) chloride (see Vol. ElOa, pp 421-423). ... 

Deoxy-2 -fluoro-4 -thio-L-ara/)z o-nucleosidcs 195 were synthesized starting from D-xylose via the 4-tluo-i,-arabinitol derivative 151 as a key intermediate (Scheme 54). Introduction of fluorine at C-2 of 151 with DAST yielded 193, which was transformed into tliio sugar 194 by oxidation and Pummerer rearrangement. Coupling of 194 witli the base and debenzylation afforded 195. The thymine analogue exhibited a moderate activity against both HSV-1 and HSV-2. 

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