The fragmentation of polyfluorinated benzylic alcohols: the first observation of pentafluorophenyl anion as a good leaving group

Treatment of a series of pentafluorobenzylic alcohols with sodium methoxide in DMSO results in a rapid carbon–carbon cleavage reaction, yielding a ketone or aldehyde as well as pentafluorobenzene, which undergoes subsequent nucleophilic aromatic substitution (NAS). In methanol solvent, the fragmentation is very slow, and NAS without fragmentation occurs almost exclusively. In methanol/DMSO mixtures, both processes are observed simultaneously. This appears to be the first report of the fragmentation of pentafluorobenzylic alcohols.