[O:1]=[C:2]([C:8]1[CH:13]=[CH:12][C:11]([C:14]2[CH:19]=[CH:18][C:17]([O:20][C:21]([F:24])([F:23])[F:22])=[CH:16][CH:15]=2)=[CH:10][CH:9]=1)[CH2:3][CH2:4][C:5]([OH:7])=[O:6].[CH3:25]OC(OC)(C)C.C[Si](Cl)(C)C>CO>[CH3:25][O:6][C:5](=[O:7])[CH2:4][CH2:3][C:2](=[O:1])[C:8]1[CH:9]=[CH:10][C:11]([C:14]2[CH:19]=[CH:18][C:17]([O:20][C:21]([F:22])([F:23])[F:24])=[CH:16][CH:15]=2)=[CH:12][CH:13]=1Crude 4-oxo-4-[4′-(trifluoromethoxy)-1,1′-biphenyl-4-yl]butyric acid (25 g, content: 65%, GC, silylated, 100% method) is dissolved in a mixture of methanol (50 ml) and 2,2-dimethoxypropane (11.5 g, 110 mmol), treated with trimethylsilyl chloride (0.75 g, 7 mmol) and stirred at 50° C. for 16 h. The reaction mixture is then concentrated and the residue is recrystallized from toluene.
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