Benzylic C[sbnd]H fluorination over supported silver catalyst

Abstract

Benzylic CH fluorination is the straightforward method for the synthesis of fluoromethylarenes, which are utilized as oxygen mimics in molecules such as nucleotides, phosphate esters and sulfate esters. We reveal that silver particles supported on a metal oxide act as an efficient catalyst for the benzylic CH fluorination of 4-methylbiphenyl with 1-fluoro-4-methyl-1,3-diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate) (Selectfluor II) as a fluorinating reagent to give 4-(fluoromethyl)-1,1′-biphenyl, whereas silver oxides resulted in aromatic fluorination. Among the catalysts tested, Ag/SiO2 exhibited the highest activity for fluorination to give the fluorinated product in 75% yield. This system was applicable to larger-scale fluorination. Mechanistic studies revealed that the present fluorination likely involves single electron transfer (SET) processes between Ag particles and 4-methylbiphenyl to afford radical species.