To a mixture of dimethylformamide (1000 ml) and 4-chloro-2-fluoro-fluoren-9-one (204 g) was added potassium carbonate (36.4 g), and the mixture was stirred in a water bath. To this mixture was added dropwise trimethyl(trifluoromethyl)silane (156 ml) over 30 min, and the mixture was further stirred at room temperature for 30 min. To the reaction mixture was added cesium fluoride (173 g), ethyl bromoacetate (75 ml) was added dropwise over 20 min, and the mixture was stirred at room temperature. Water (1000 ml) was added to the reaction mixture, and the mixture was placed in a separatory funnel, and extracted with ethyl acetate (1000 ml). The organic layer was washed twice with brine (water:saturated brine=4:1, 1000 ml) and once with saturated brine (500 ml), dried over anhydrous sodium sulfate, and filtered. The filtrate was concentrated under reduced pressure to give the title compound (360 g). The obtained residue was directly used for the next reaction without further purification.
