SELECTIVE, ELECTROPHILIC FLUORINATIONS USING N-FLUORO-O-BENZENEDISULFONIMIDE

The synthesis of N-fluoro-o-benzenedisulfonimide (NFOBS, 2) and its use as an ''electrophilic'' fluorinating reagent with nucleophilic substrates is described and compared with that of N-fluorobenzenesulfonimide (NFSi, 3). NFOBS (2) is prepared in three steps in 81% overall yield from commercially available o-benzenedisulfonic acid (4) and involves treatment of o-benzenedisulfonimide (6) with dilute fluorine (10% F-2/N-2). Reaction of 2 with metal enolates, silyl enol ethers, and 1,3-dicarbonyl compounds affords the corresponding alpha-fluoro compounds in yields up to 95%, with good control of mono- and difluorination. Fluorination of ortho-metalated aromatic compounds was achieved in modest to good yields (10-80%). While the reactivities of 2 and 3 are similar, better yields were observed with the former reagent in the fluorination of metal enolates, Grignard and lithium reagents, while 3 gave better results with the ortho-lithiated aromatic substrates. The available evidence suggests an S(N)2-type mechanism for the fluorination of nucleophilic substrates by these reagents.