[C:1]1([S:7]([N:10]2[C:18]3[C:13](=[CH:14][C:15]([C:19](=[O:21])[CH3:20])=[CH:16][CH:17]=3)[CH2:12][CH2:11]2)(=[O:9])=[O:8])[CH:6]=[CH:5][CH:4]=[CH:3][CH:2]=1.[Br-:22].[Br-].[Br-].C1([N+](C)(C)C)C=CC=CC=1.C1([N+](C)(C)C)C=CC=CC=1.C1([N+](C)(C)C)C=CC=CC=1.O>C1COCC1>[C:1]1([S:7]([N:10]2[C:18]3[C:13](=[CH:14][C:15]([C:19](=[O:21])[CH2:20][Br:22])=[CH:16][CH:17]=3)[CH2:12][CH2:11]2)(=[O:8])=[O:9])[CH:2]=[CH:3][CH:4]=[CH:5][CH:6]=1The ketone from step 1 (0.310 g, 1.02 mmol) was dissolved in THF (3 ml), and phenyltrimethylammonium tribromide (PTT) (0.386 g, 1.02 mmol) was added as a solid leaving an orange solution which began to deposit a white solid immediately. Stirring for 1.5 hours leaves a colorless mixture to which water (5 ml) was added. THF was then evaporated and the resulting aqueous mixture was extracted with ethyl acetate. Drying over Na2SO4 and evaporation leaves a white crystalline solid (85% desired mono-brominated material by LC-MS, 5% starting material, 10% dibrominated) suitable for the next step. LC-MS (ES+): 381, 379 m/e.
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