CC(C)([O-])C.[K+].[F:7][C:8]1[C:13]([F:14])=[CH:12][CH:11]=[CH:10][C:9]=1[OH:15].[CH2:16]([O:18][C:19](=[O:24])[CH:20]=[C:21](Cl)[CH3:22])[CH3:17]>O1CCCC1>[CH2:16]([O:18][C:19](=[O:24])/[CH:20]=[C:21](/[O:15][C:9]1[CH:10]=[CH:11][CH:12]=[C:13]([F:14])[C:8]=1[F:7])\[CH3:22])[CH3:17]Potassium t-butoxide (11.2 g, 0.100 mol) was added to a stirred solution of 2,3-difluoro-phenol (6.58 g, 0.051 mol) in tetrahydrofuran (30 mL) at 23° C. under nitrogen and the reaction mixture was heated to reflux for 0.75 h. The reaction mixture was cooled to 23° C. and a solution of 3-chloro-but-2-enoic acid ethyl ester (prepared as in Example 191 7.50 g, 0.050 mol) in tetrahydrofuran (40 mL) was added to the reaction mixture. The reaction mixture was refluxed for an additional 3 h. After this time, the mixture was concentrated in vacuo and the residue was diluted with water and extracted with diethyl ether. The organic layer was then washed with 5% aqueous sodium hydroxide solution followed by a saturated aqueous sodium chloride solution, dried over sodium sulfate and concentrated in vacuo to afford (E)-3-(2,3-difluoro-phenoxy)-but-2-enoic acid ethyl ester (8.01 g, 66%) as a yellow oil.
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