Two interesting papers in Angewandte Chemie International Edition ( Yamada S et al, pp2215-8, and Anbarasan P et al pp 2219-2222) describe ways of introducing F into a specific position in an aromatic or heteroaromatic structure. The first paper, from the group of Knochel, treats a Grignard reagent (as the LiCl complex) with a fluorinating agent such as N-fluorobenzenesulfonimide to give high yields of the desired fluoro-aromatic. Interestingly the reaction is very solvent dependent, with poor yields in THF and other ethereal solvents but good yields in a mixture of DCM and perfluorodecalin (4:1).

The second paper, from the group of Beller at Rostock is on the same reaction but uses a variety of N-F fluorinating agents. In their cases the best solvent was found to be heptane or perfluorobutyl methyl ether.

Ultimately this process is the replacement of Cl or Br with F, and is an alternative to other halogen exchange processes. This new process seems to be relatively easy to carry out, uses low temperatures and has wide scope, but clearly uses much more expensive reagents, so may not get widely used on large scale.