Fluorosulfonic acid ester

An example of an er-fluorosulfonic acid ester is provided in the same scheme. Lastly, there is a comparison of a bis-sulfone and the carbanion formed by deprotonation. Note the significant shielding of the fluorine substituent in the carbanion. 

The action of oxonium salts on vinylogous amides affords iminium salts (71 equation 44), which are useful for synthetic purposes in heterocyclic chemistry. ° " - Alkyldiphenylsulfonium tetrafluoro-borates (72 equation 45) were recommended as reagents which alkylate amides and lactams under smooth conditions.2 2 With the aid of fluorosulfonic acid esters as well as with trifluorometh-anesulfonic acid esters, - - which have alkylation power comparable to oxonium salts, iminium salts, e.g. (73) and (74 Scheme 5), could be synthesized from amides, - vinylogous amides and lactams. Trimethylsilyloxymethyleneiminium salts (75 equation 46) are accessible by reacting tri-methylsilyltrifluoromethanesulfonate with amides. - ... 

A mixture of fluorosulfonic acid and dimethyl sulfate distilled in glass -> methyl fluorosulfonate. Y > 80%. - Fluorosulfonic acid esters are excellent alkylating agents. F. e. and listing of good alkylating agents s. M. G. Ahmed et al., Chem. Commun. 1968, 1533. 

Chlorosulfonic acid esters Sulfuric acid chloride esters 15 Fluorosulfonic acid esters... 

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