C[O:2][C:3](=[O:23])[CH:4]([N:9]1[CH2:13][C:12]([O:14][C:15]2[CH:20]=[CH:19][CH:18]=[CH:17][C:16]=2[Cl:21])=[CH:11][C:10]1=[O:22])[CH2:5][CH:6]([F:8])[F:7].O1CCCC1.O.[OH-].[Li+]>O>[Cl:21][C:16]1[CH:17]=[CH:18][CH:19]=[CH:20][C:15]=1[O:14][C:12]1[CH2:13][N:9]([CH:4]([CH2:5][CH:6]([F:8])[F:7])[C:3]([OH:23])=[O:2])[C:10](=[O:22])[CH:11]=1A mixture of 2-[4-(2-chloro-phenoxy)-2-oxo-2,5-dihydro-pyrrol-1-yl]-4,4-difluoro-butyric acid methyl ester (790 mg, 2.28 mmol) in a 1:1 solution of tetrahydrofuran:water (20 mL) was treated with lithium hydroxide monohydrate (230 mg, 4.56 mmol). The mixture was stirred for 2 h at 25° C. After such time, the mixture was concentrated in vacuo to remove the tetrahydrofuran and then diluted with water, and the pH adjusted to pH=5 with 1N aqueous hydrochloric acid and extracted with ethyl acetate. The organic layer was dried over sodium sulfate and concentrated in vacuo to afford 2-[4-(2-chloro-phenoxy)-2-oxo-2,5-dihydro-pyrrol-1-yl]-4,4-difluoro-butyric acid (571 mg, 75%) as a cream colored solid: HR-ES-MS m/z calculated for C14H12NO4ClF2 [M+H]+ 332.0496, observed 332.0496.
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