potassium-fluoride and trifluoromethanesulfonic-acid

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).

Topics: Catalysis; Copper; Fluorides; Fluorine; Mesylates; Molecular Structure; Potassium Compounds

This Communication describes the Cu(OTf)2-mediated fluorination of aryltrifluoroborates with KF. The reaction proceeds under mild conditions (at 60 °C over 20 h) and shows a broad substrate scope and functional group tolerance. The Cu is proposed to play two separate roles in this transformation: (1) as a mediator for the aryl–F coupling and (2) as an oxidant for accessing a proposed Cu(III)(aryl)(F) intermediate.

Topics: Boranes; Fluorides; Hydrocarbons, Fluorinated; Mesylates; Molecular Structure; Potassium Compounds