[Mg].BrCCBr.[Br:6][C:7]1[CH:14]=[CH:13][C:10]([CH2:11]Br)=[CH:9][CH:8]=1.[O:15]=[C:16]1[CH2:21][CH2:20][N:19]([C:22]([O:24][C:25]([CH3:28])([CH3:27])[CH3:26])=[O:23])[CH2:18][CH2:17]1.[Cl-].[NH4+]>C(OCC)C>[Br:6][C:7]1[CH:14]=[CH:13][C:10]([CH2:11][C:16]2([OH:15])[CH2:17][CH2:18][N:19]([C:22]([O:24][C:25]([CH3:27])([CH3:26])[CH3:28])=[O:23])[CH2:20][CH2:21]2)=[CH:9][CH:8]=1To a suspension of magnesium (2.9 g) in diethyl ether (50 mL) was added dropwise 1,2-dibromoethane (0.90 mL) at room temperature, and the reaction mixture was vigorously stirred at room temperature for 20 min. To the reaction mixture was added dropwise a solution of 4-bromobenzyl bromide (25 g) in diethyl ether (150 mL) over 30 min or more at 0° C., and then added dropwise a solution of tert-butyl 4-oxopiperidine-1-carboxylate (16 g) in diethyl ether (200 mL) over 30 min or more 0° C. The reaction mixture was allowed to warm to room temperature, and stirred at room temperature for 3 hr. To the reaction mixture was added saturated aqueous ammonium chloride solution (200 mL), and the mixture was extracted with ethyl acetate. The extract was dried over anhydrous sodium sulfate, and the solvent was evaporated under reduced pressure. The residue was purified by silica gel column chromatography (ethyl acetate/hexane) to give the title compound (12 g).
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