[CH3:1][O:2][C:3]1[C:8]([CH3:9])=[CH:7][C:6]([C:10](=[O:12])[CH3:11])=[C:5]([CH3:13])[CH:4]=1.C([O:16][C:17](=O)[C:18]([F:21])([F:20])[F:19])C.[O-]CC.[Na+].Cl>C(O)C.O.O1CCCC1>[F:19][C:18]([F:21])([F:20])[C:17](=[O:16])[CH2:11][C:10]([C:6]1[CH:7]=[C:8]([CH3:9])[C:3]([O:2][CH3:1])=[CH:4][C:5]=1[CH3:13])=[O:12]
At room temperature, to a mixture of 1-(4-methoxy-2,5-dimethylphenyl)-ethanone (described in Reference Preparation example 82) 5 g and tetrahydrofuran 200 ml was added trifluoroacetic acid ethyl ester 7.9 g and 20% sodium ethoxide solution in ethanol 19 g. The resulting mixture was stirred with heating under reflux for seven hours, and then to the reaction mixture was added water 70 ml, and the resulting mixture was acidified with 6N aqueous hydrochloric acid solution. The resulting mixture was extracted with ethyl acetate. The organic layer was washed with water and was dried over anhydrous magnesium sulfate, and was then concentrated under reduced pressure. The resulting residue was subjected to a silica gel column chromatography to give 4,4,4-trifluoro-1-(4-methoxy-2,5-dimethyl-phenyl)-butane-1,3-dione 6.8 g.
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