Among the many organic fluorine compounds containing nitrogen and sulfur, dialkylaminotrifluorosulfuranes and bis(dialkylamino)difluorosulfuranes have become very useful fluorinating agents. The first representative of this group, dimethylaminosulfur trifluoride was prepared in 1964, followed in 1970 by diethylaminosulfur trifluoride, which became popular under the acronym DAST. Both compounds were synthesized by treatment of the appropriate dialkylaminotrimethylsilane with sulfur tetrafluoride.
Subsequently, bis(dialkylamino)sulfur difluorides were prepared by the reaction of dialkylaminosulfur trifluorides with dialkylaminotrimethylsilanes.
Both classes of compounds were found to convert alcohols into fluorides, and aldehydes and ketones into geminal difluorides:
Further uses include the preparation of acyl and sulfonyl fluorides from carboxylic and sulfonic acids and the conversion of sulfoxides into α-fluoroalkyl sulfides.
Later, the reaction of bis(dialkylamino)difluorosulfuranes with dialkylaminotrimethylsilanes was shown to give tris(dialkylamino)sulfonium difluorotrimethylsilicates (TASF).
These salts no longer react with alcohols or carbonyl compounds, but they convert even relatively unreactive halides, such as primary chlorides, into fluorides under very mild conditions. Furthermore, they are readily soluble in organic solvents and are useful sources of “naked,” unsolvated fluoride ion.
This chapter deals with the preparation of all three classes of reagents and their use as fluorinating agents. The literature is covered exhaustively until the end of 1984; some papers beyond that date are included.