[F:1][C:2]([F:11])([F:10])[C:3]1([CH2:8][OH:9])[CH2:7][CH2:6][CH2:5][CH2:4]1.CC(C)([O-])C.[K+].[Cl:18][C:19]1[C:20](F)=[CH:21][C:22]([F:28])=[C:23]([CH:27]=1)[C:24]([OH:26])=[O:25].Cl>CS(C)=O>[Cl:18][C:19]1[C:20]([O:9][CH2:8][C:3]2([C:2]([F:10])([F:11])[F:1])[CH2:7][CH2:6][CH2:5][CH2:4]2)=[CH:21][C:22]([F:28])=[C:23]([CH:27]=1)[C:24]([OH:26])=[O:25]To a solution of (1-(trifluoromethyl)cyclopentyl)methanol (2.80 g, 16.65 mmol) in anhydrous dimethylsulfoxide (50 ml) was added potassium tert-butoxide (4.50 g, 40.106 mmol) and the reaction mixture was stirred at ambient temperature for 30 minutes. 5-chloro-2,4-difluorobenzoic acid (3.20 g, 16.62 mmol) was added to the reaction mixture, and stirring was continued for 2 hours. The reaction mixture was acidified to pH=1 with 5% aqueous hydrochloric acid solution and extracted with ethyl acetate, the combined organic extracts was washed with brine; dried over anhydrous sodium sulfate and concentrated in vacuo. Purification of the residue by column chromatography (30% ethyl acetate in hexanes) afforded the title compound (5.00 g, 88%) containing o-substituted regioisomer, which was used for next step without further purification: MS (ES−) m/z 339.2, 341.2 (M−1).
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