Under a nitrogen atmosphere, to a solution of 2′-fluoro-5′-methoxybiphenyl-2,4-diol (10.6 g) in toluene (80 mL) were added triisopropylsilyl trifluoromethanesulfonate (18 mL) and 2,6-dimethylpyridine (8.0 mL) at −15° C., and the mixture was stirred for 3 hr. To the reaction mixture was added saturated aqueous ammonium chloride solution, and the mixture was extracted with ethyl acetate. The extract was washed with saturated brine and dried over anhydrous sodium sulfate. The solvent was evaporated under reduced pressure and the residue was purified by silica gel column chromatography (ethyl acetate/hexane) to give the title compound (10.5 g) as a pale-yellow oil.
