[F:1][C:2]1([F:13])[CH2:7][CH2:6][CH:5]([CH2:8][CH2:9][C:10]([OH:12])=O)[CH2:4][CH2:3]1.C(Cl)(=O)C(Cl)=O.[F:20][C:21]([F:26])([F:25])C(O)=O.N1C=CC=CC=1>ClCCl.CN(C=O)C>[F:13][C:2]1([F:1])[CH2:3][CH2:4][CH:5]([CH2:8][CH2:9][C:10](=[O:12])[C:21]([F:26])([F:25])[F:20])[CH2:6][CH2:7]13-(4,4-Difluorocyclohexyl)propionic acid (500 mg, 2.60 mmol) obtained in step 3 of Example 34 was dissolved in dichloromethane (5.0 mL), and the solution was stirred at room temperature for 30 minutes after adding oxalyl chloride (0.430 mL, 5.12 mmol) and DMF (0.010 mL). The solvent was then evaporated under reduced pressure. The residue was dissolved in dichloromethane (10 mL), and the mixture was cooled to −10° C., and stirred at room temperature for 2 hours after adding anhydrous trifluoroacetic acid (2.20 mL, 15.8 mmol) and pyridine (1.70 mL, 21.3 mmol). Upon being cooled to −10° C., the mixture was extracted with dichloromethane after gently adding water in a manner that keeps the internal temperature at or below 0° C. The organic layer was washed with 3 mol/L hydrochloric acid and a saturated sodium hydrogen carbonate aqueous solution, and then with saturated brine, and dried over anhydrous sodium sulfate. The solvent was then evaporated under reduced pressure. The residue was purified by silica gel chromatography (hexane/ethyl acetate=70/30) to give 4-(4,4-difluorocyclohexyl)-1,1,1-trifluorobutan-2-one (204 mg, yield 35%).
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