Fluoro-Pummerer reaction fluorides

Organic fluorine compounds and methods for their preparation are the central topic of the next four procedures. Much of the synthetic versatility of methyl phenyl sulfone is embodied in FLUOROMETHYL PHENYL SULFONE and the fluoro Pummerer reaction of methyl phenyl sulfoxide with DAST is a key step in its preparation. The utility of this fluoromethyl sulfone in the preparation of fluoroalkenes Is demonstrated in a companion procedure for Z-[2-(FLUOROMETHYLENE) CYCLOHEXYL]BENZENE, a procedure with several prominent stereoselective features. Geminal difluoroalkenes are featured in the following procedure. (3,3 DIFLUOROALLYL)TRIMETHYLSILANE is prepared by a method in which the radical addition of dibromodifluoromethane to alkenes and the selective reduction of a-bromoalkylsilanes are key steps. A procedure for nucleophilic introduction of the trifluoromethyl group completes this set. The key reagent, (TRIFLUOROMETHYL)-TRIMETHYLSILANE is obtained by reductive coupling of TMS chloride and bromotrifluoromethane. Liberation of a CF3- equivalent with fluoride ion in the presence of cyclohexanone affords 1-TRIFLUOROMETHYL-1-CYCLOHEXANOL. 

The literature on Pummerer chemistry is quite extensive, and multiple variants are described. However, looking deeply into these alternatives, it becomes apparent that most of them are based on the same principle, and the only variation is the nucleophile source. One example of this is the so-called fluoro-Pummerer reaction, which is in fact a fluoride addition to the normal Pummerer intermediate. The distinguishing feature is the generation of the thionium intermediate, using (diethylamino)sulfur trifluoride (DAST) in combination with metals (Scheme 20.391. DAST is known as a source of nucleophilic fluoride and has been widely used for this purpose. A review on the fluoro-Pummerer reaction was published by Haufe and coworkers in 2012. ... 

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). ... 

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