Electrophilic fluorination of N,N-dimethylaniline, N,N-dimethylnaphthalen-1-amine and 1,8-bis(dimethylamino)naphthalene with N–F reagents

Reaction of N,N-dimethylaniline, N,N-dimethylnaphthalen-1-amine and 1,8-bis(dimethylamino)naphthalene (proton sponge) with 1-chloromethyl-4-fluorodiazonia-bicyclo[2.2.2]octane bis(tetrafluoroborate) (Selectfluor) and N-fluorobenzenesulfonimide (NFSI) has been studied under various conditions. Unlike the proton sponge, which is fluorinated rather selectively at the ortho-position to NMe2 group, producing 2-fluoro derivatives in moderate yield, two other amines react with Selectfluor and NFSI with strong tarring and the formation of complex mixtures of the corresponding biaryls, biarylmethanes and N-demethylated products. 2-Fluoro and 4-fluoro derivatives are also formed in minor quantities with the former isomer being predominant. Using the NFSI–ZrCl4 system results in competitive chlorination of the aromatic ring.