In argon atmosphere, a liquid mixture of 6.00 g (15.0 mmol) of 2-bromo-9,9-dimethyl-7-(naphthalene-2-yl)-9H-fluorene and 150 ml of dry THF was cooled to −60° C., and 11.6 ml (18.0 mmol) of a 1.55 M hexane solution of n-butyllithium was added dropwise under stirring. Then, the reaction mixture was stirred at −70° C. for 2 h. The reaction solution was cooled again to −70° C., and 8.48 g (45.1 mol) of triisopropyl borate was added dropwise. The reaction mixture was heated up to room temperature, stirred for one hour, and left standing overnight. The reaction mixture was cooled on ice bath, added with a 6 N hydrochloric acid, and stirred at room temperature for one hour. The reaction mixture was added with dichloromethane and allowed to stand for separation into liquid phases. The organic phase was washed with water and dried over sodium sulfate. The solvent was distilled off under reduced pressure, and the residue was purified by silica gel chromatography to obtain 3.50 g (yield: 64%) of 9,9-dimethyl-7-(naphthalene-2-yl)-9H-fluorene-2-ylboronic acid.
