[Cl:1][C:2]1[CH:7]=[CH:6][C:5]([CH:8]([CH:14]2[CH2:18][CH2:17][CH2:16][C:15]2([F:20])[F:19])[C:9]([O:11]CC)=[O:10])=[CH:4][CH:3]=1.C1COCC1.[OH-].[Na+].Cl>CO.O>[Cl:1][C:2]1[CH:3]=[CH:4][C:5]([CH:8]([CH:14]2[CH2:18][CH2:17][CH2:16][C:15]2([F:19])[F:20])[C:9]([OH:11])=[O:10])=[CH:6][CH:7]=12.70 g (8.92 mmol) of ethyl (4-chlorophenyl)(2,2-difluorocyclopentyl)acetate (diastereomer mixture) were dissolved in 10 ml of methanol, 10 ml of THF and 5 ml of water, and 7.13 g (89.18 mmol) of 50% strength aqueous sodium hydroxide solution were added at RT. The reaction mixture was stirred at RT overnight. The mixture was then diluted with water and acidified with hydrochloric acid. The aqueous phase was extracted three times with ethyl acetate, the combined organic phases were dried over magnesium sulphate and concentrated under reduced pressure and the residue was dried under high vacuum. This gave 2.39 g of the title compound (97.6% of theory, diastereomer ratio about 1:1).
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