[Br:1][C:2]1[CH:7]=[CH:6][C:5]([CH:8]2[CH2:12][CH2:11][CH2:10][NH:9]2)=[CH:4][C:3]=1[F:13].C(=O)([O-])[O-].[K+].[K+].Cl[C:21]([O:23][CH2:24][C:25]1[CH:30]=[CH:29][CH:28]=[CH:27][CH:26]=1)=[O:22]>O1CCOCC1.O>[Br:1][C:2]1[CH:7]=[CH:6][C:5]([CH:8]2[CH2:12][CH2:11][CH2:10][N:9]2[C:21]([O:23][CH2:24][C:25]2[CH:30]=[CH:29][CH:28]=[CH:27][CH:26]=2)=[O:22])=[CH:4][C:3]=1[F:13]
2-(4-Bromo-3-fluorophenyl)pyrrolidine (12.5 g, 51.4 mmol) was dissolved in a mixture of dioxane (180 mL) and water (120 mL) and treated with potassium carbonate (28.4 g, 0.21 mol) and benzyl chloroformate (9.65 g, 56.5 mmol) at ambient temperature overnight. The mixture was partitioned between ethyl acetate and brine. The organic phase was concentrated and the residue was purified by flash chromatography on silica gel using a gradient of 5-20% ethyl acetate in petroleum ether to give benzyl 2-(4-bromo-3-fluorophenyl)pyrrolidine-1-carboxylate as a yellow solid (15.3 g, yield 82%). LC-MS (ESI) m/z: 378 (M+1)+.
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