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

The synthesis of N-fluoro-o-benzenedisulfonimide (NFOBS, 2) and its us e as an ''electrophilic'' fluorinating reagent with nucleophilic subst rates is described and compared with that of N-fluorobenzenesulfonimid e (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-d icarbonyl compounds affords the corresponding alpha-fluoro compounds i n yields up to 95%, with good control of mono- and difluorination. Flu orination of ortho-metalated aromatic compounds was achieved in modest to good yields (10-80%). While the reactivities of 2 and 3 are simila r, better yields were observed with the former reagent in the fluorina tion of metal enolates, Grignard and lithium reagents, while 3 gave be tter results with the ortho-lithiated aromatic substrates. The availab le evidence suggests an S(N)2-type mechanism for the fluorination of n ucleophilic substrates by these reagents.