Mild copper-catalyzed fluorination of alkyl triflates with potassium fluoride.
A chemoselective catalytic fluorination of alkyl triflates is described using potassium fluoride as a fluoride source. Excellent yields of the desired alkyl fluorides are obtained after one hour at 45 °C using 2 mol% of the copper catalyst. With 10 mol% of the catalyst, full conversion can be achieved in less than 10 minutes at 45 °C, and thus makes this procedure potentially suited for the preparation of (18) F-labeled PET probes. As a result of the mild reaction conditions, only the substitution products are observed with no evidence of common side reactions, such as elimination. Reported is a preliminary study of the reaction scope, which demonstrates that the fluorination can be performed in the presence of a wide range of functional groups. Evidence suggests an unusual role of the [IPrCuOTf] catalyst as a phase-transfer catalyst and points to [IPrCuF] as the active fluorinating reagent (IPr=1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene).
Department of Chemistry, University of Washington, Seattle, WA 98195 (USA).
Hester
H
Dang
Melrose
M
Mailig
Gojko
G
Lalic
D002384:Catalysis; D003300:Copper / Q000737:chemistry*; D005459:Fluorides / Q000737:chemistry*; D005461:Fluorine / Q000737:chemistry*; D008698:Mesylates / Q000737:chemistry; D015394:Molecular Structure; D017680:Potassium Compounds / Q000737:chemistry*
D008698:Mesylates; D017680:Potassium Compounds; D005461:Fluorine; D003300:Copper; C033320:potassium fluoride; C012077:trifluoromethanesulfonic acid; D005459:Fluorides
carbenes; copper; fluorine; isotopic labeling; phase-transfer catalysis