A mixture of 4-amino-5-cyano-2-fluoro-6-methylbiphenyl-3-yl 2,2-dimethylmalonate (I-63) (500 mg, 1.12 mmol), p-toluenesulfonic acid monohydrate (21 mg, 0.112 mmol) and toluene (20 ml) was heated under reflux for 2 hours. After cooling, the reaction liquid was diluted with ethyl acetate, successively washed with an aqueous saturated sodium hydrogencarbonate solution and saturated brine, dried on anhydrous magnesium sulfate, then the solvent was evaporated away to obtain a pale brown residue. The resulting residue was purified by silica gel column chromatography (n-hexane:ethyl acetate=6:1) to obtain the entitled compound (411 mg, 86%) as a colorless solid.
