Diethylaminosulfur trifluoride alkylation with

SF4 and diethylaminosulfur trifluoride (DAST) give alkyl fluorides not only from tertiary and secondary, as with HF, but also from primary alcohols (equation 36). Reactions with gaseous, corrosive SF4 (b.p. -38 °C) usually require temperatures of 20-100 C. The special equipment needed for reactions with toxic gases under pressure make the use of SF4 inconvenient. The introduction of DAST has removed the handling problems. DAST is a liquid reagent made from SF4 and trimethylsilyldiethyl-... 

In the laboratory of G.A. Posner, semisynthetic antimalarial trioxanes in the artemisinin family were prepared via an efficient Friedel-Crafts alkylation using a pyranosyi fluoride derived from the natural trioxane lactone artemisinin. The alkylating agent, pyranosyi fluoride, was prepared from the lactone in two steps reduction to the lactol followed by treatment with diethylaminosulfur trifluoride. The highly chemoselective alkylation was promoted by BF3-OEt2 and several electron-rich aromatic and heteroaromatic compounds were alkylated in moderate to high yield using this method. 

Treatment of methyl phenyl sulfoxide with diethylaminosulfur trifluoride (DAST), in the presence of antimony trichloride provides 159 in quantitative yield (66). The reaction proceeds in good yield with dialkyl sulfoxides and alkyl aryl sulfoxides (163). Reoxidation of the a-fluorosulfide (165) to the corresponding sulfoxide (161), followed by pyrolysis, provides a direct synthesis of fluoroolefins (65). The reaction is believed to proceed by a Pummerer-type mechanism (l.e., a fluoro-Pummerer reaction, Scheme 48). Similarly, Umemoto (67) reported that N-fluorocollidine (167) converted sulfides to ot-fluorosulfides (170) presumably via an S-fluorosulfonium cation species 168 (Scheme 49). The synthetically challenging fluorovinyl ether nucleosides (175) and (176) were prepared using the fluoro-Pummerer reaction (Scheme 50) (60) the (E)-isomer (175) could be isomerized to 176 under photolytic conditions. Finch and co-workers (69) converted 160 to the sulfoximine 178 and demonstrated the utility of this compound as a mild fluoromethylene synthon (Scheme 51). Base-catalyzed condensation 178 with a carbonyl compound gave 179 which afforded... 

Hydrogen fluoride (HF) fails to convert alcohols to the corresponding fluorides. Sulfur tetrafluoride or its derivative, diethylaminosulfur trifluoride (DAST (CH3CH2)2NSp3), is required for the conversion of alcohols to the corresponding fluorides. As with analogous proton-catalyzed reactions and as shown in Scheme 8.29, alkyl fluoride formation results from mixtures of SnI and Sn2 processes. 

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