[CH2:1]([O:8][C:9]([N:11]1[CH2:16][CH2:15][C:14](=[O:17])[CH2:13][CH2:12]1)=[O:10])[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.CCN(C(C)C)C(C)C.FC(F)(F)S(O[Si](C)(C)C)(=O)=O.[Br:39]N1C(=O)CCC1=O>C(Cl)Cl>[Br:39][CH:13]1[C:14](=[O:17])[CH2:15][CH2:16][N:11]([C:9]([O:8][CH2:1][C:2]2[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=2)=[O:10])[CH2:12]1To a cooled (0° C.) solution of N-benzyloxycarbonyl-4-piperidone (501, 27.3 g 117 mmol) in DCM (3 ml/mmol) was added DIPEA (25.5 ml, 146.2 mmol, 1.25 eg) and trimethylsilyl trifluoromethane sulfonate (25.4 ml, 141 mmol, 1.2 eg). The mixture was stirred for 30 minutes at 0° C. Next, N-bromosuccinimide (21.2 g, 119.3 mml, 1.02 eg) was added and stirring was continued for 16 hrs at room temperature. The reaction mixture was washed with 5% NaHCO3 and the organic layer was dried (MgSO4) and subsequently concentrated under reduced pressure. The resulting oil was purified by silica gel chromatography (diethyl ether/petroleum ether, 1/1 to 1/0, v/v, Rf 0.1) giving 502 in a yield of 90% as a yellow oil.
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