[C:1]1(=[O:19])[N:5]([CH2:6][CH2:7][CH2:8][CH2:9][CH2:10][C:11]([OH:13])=[O:12])[C:4](=[O:14])[C:3]2=[CH:15][CH:16]=[CH:17][CH:18]=[C:2]12.[Br:20]Br.S(=O)(O)[O-].[Na+].C(=O)(O)[O-].[Na+]>O>[Br:20][CH:10]([CH2:9][CH2:8][CH2:7][CH2:6][N:5]1[C:4](=[O:14])[C:3]2=[CH:15][CH:16]=[CH:17][CH:18]=[C:2]2[C:1]1=[O:19])[C:11]([OH:13])=[O:12]Combine 6-phthalimidohexanoic acid (12.7 g, 48 mmol) and dry red phosphorous (1.95 g, 63 mmol). Cool in an ice bath and add bromine (12.7 mL, 246 mmol) dropwise. Warm to room temperature and then heat to 80° C. After 3 hours, cool the reaction mixture to ambient temperature, pour into water (300 mL) containing sodium bisulfite, and neutralize using solid sodium bicarbonate and extract with diethyl ether (about 150 mL). Acidify the aqueous layer with concentrated hydrochloric acid to give a solid. Collect the solid by filtration and dry to give the title compound (15 g, 91.5% yield, 73.2% for both steps).
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