Regiospecific replacement of fluorine by hydrogen in an aromatic ring induced by a rare earth organometallic

Pentafluorobenzoic acid reacts with YbCp 2 (dme) to yield, after hydrolysis, 2,3,4,5-tetrafluorobenzoic acid. Conversion is near quantitative with activated magnesium as a coreductant and there is evidence for catalytic turnover in ytterbium on addition of a cyclopentadiene source. Reduction of 2,6-F 2 C 6 H 3 CO 2 H to o -FC 6 H 4 CO 2 H and of o -FC 6 H 4 CO 2 H to PhCO 2 H has also been achieved. 2,3,4,5-Tetrafluorobenzoic acid has been obtained in near quantitative yield from reaction of C 6 F 5 CO 2 H with YbCp 2 (dme) and activated magnesium followed by hydrolysis, and there is catalytic turnover in ytterbium on addition of a cyclopentadiene source.