[2923-28-6] · CAgF3O3S · Silver(I) Trifluoromethanesulfonate · (MW 256.95)
(reactive triflating agent and source of soluble silver ions useful for formation of electrophilic onium species,1 and promotion of Friedel-Crafts,2 nucleophile-alkene cyclization,3 and esterification4 reactions)
Alternate Name: silver triflate.
Physical Data: mp 356 °C.
Solubility: sol typical organic solvents.
Form Supplied in: white solid; widely available.
Preparative Method: can be prepared from the barium salt via treatment with dil H2SO4 followed by neutralization with Ag2CO3.5
Handling, Storage, and Precautions: light sensitive; irritant. Use in a fume hood.
Oxygen- and nitrogen-containing molecules bearing an a-nucleofuge such as a halide or sulfur are converted by AgOTf to highly electrophilic onium (eq 1)1 or iminium (eq 2)6 species. The intermediacy of a planar cation is substantiated by the formation of the same diastereomer from either substrate isomer in some cyclization reactions (eq 1).
This reaction type has enjoyed wide application in carbohydrate chemistry, as anomeric carbons can be easily functionalized with high stereospecificity by silyl enol ethers (eq 3, RŽ = Ph,7 H8) and other nucleophiles.
When treated with AgOTf, alkyl,2 acyl (eq 4),9 and sulfonyl10 halides are converted to extremely electrophilic triflate species that react rapidly with even deactivated11 aromatic rings in the absence of catalysis. Benzylic chloroformates participate similarly (eq 5).12 Aromatic rings are also efficiently vinylated13 and iodinated14 via AgOTf-promoted processes.
AgOTf induces a highly diastereoselective cyclization of amino ketenes wherein asymmetry is induced by an adjacent stereogenic center and is dependent upon silver concentration (eq 6).3 Acetylenic oxy-Cope rearrangements are also facilitated by AgOTf (eq 7),15 and a mild, high-yield esterification utilizes AgOTf in the presence of Titanium(IV) Chloride (eq 8).4
T. Howard Black
Eastern Illinois University, Charleston, IL, USA