A 100-ml flask was charged with 5 ml of toluene, 0.24 g (2 mmol) of anhydrous magnesium sulfate and 0.11 ml (2 mmol) of concentrated sulfuric acid, and they were vigorously stirred. To this mixture was added 2.12 g (10 mmol) of 4′-methyl-2-biphenylcarboxylic acid, and isobutene gas (98 mmol) was introduced thereto at a flow rate of 1.2 liter/min for 2 minutes. The resulting mixture was stirred at room temperature for 6 hours. After having confirmed that almost all of the peaks ascribed to 4′-methyl-2-biphenylcarboxylic acid disappeared by HPLC, 4 ml of deionized water was poured into the mixture, and sufficiently stirred. Thereafter, the mixture was allowed to stand to separate into layers. The upper toluene layer was taken out therefrom, and the toluene layer was washed with a 1.5 M aqueous sodium hydroxide, and dried over anhydrous magnesium sulfate. Thereafter, the toluene layer was concentrated by distilling off toluene by using a rotary evaporator, to give 2.54 g of tert-butyl 4′-methyl-2-biphenylcarboxylate as crystals (yield: 95% based on 4′-methyl-2-biphenylcarboxylic acid, purity by HPLC: 99.9%).
