Direct electrophilic fluorination of naproxen with NF-reagents

A novel effective protocol has been developed for direct fluorination of naproxen using the electrophilic fluorinating reagents 1-chloromethy1-4-fluoro-l,4-diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate) (Selectfluor™, F-TEDA-BF4) and N-fluorobenzenesulfonimide (NFSI) in MeCN and H2O solvents with the formation of 2-(5-fluoro-6-methoxynaphthalen-2-yl)propionic and 2-(5,5-difluoro-6-oxo-5,6-dihydronaphthalen-2-yl)propionic acids. The reaction of naproxen with an excess of Selectfluor (mol. ratio NF-reagent/naproxen = 2.2) in MeOH gives methyl 2-(5,5-difluoro-6,6-dimethoxy-5,6-dihydronaphthalen-2-yl)propionate as the main product. The mechanistic aspects of the reactions and X-ray data of products are discussed.