DAST reagent, fluorine introduction,

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. 

Synthesis of Fluorinated Pyrroles As described in the previous Section 3.2.1, the availability of hydroxypyrrolidines provided convenient functionality for introduction of fluorine, and many syntheses were based on either nucleophihc displacement of oxygen functionality by fluoride or deoxyfluorination with DAST or other such reagents. In contrast, many fundamentally different methods have been used to prepare fluorinated pyrroles. 

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