[Br:1][C:2]1[C:7](=[O:8])[N:6]2[CH:9]=[C:10]([F:13])[CH:11]=[CH:12][C:5]2=[N:4][C:3]=1[CH:14]([NH:16]C(=O)OCC1C=CC=CC=1)[CH3:15].B(Br)(Br)Br.O.C(=O)(O)[O-].[Na+]>ClCCl>[NH2:16][CH:14]([C:3]1[N:4]=[C:5]2[CH:12]=[CH:11][C:10]([F:13])=[CH:9][N:6]2[C:7](=[O:8])[C:2]=1[Br:1])[CH3:15]E2 (312 mg, 0.74 mmol) was dissolved in 18 mL of anhydrous dichloromethane. BBr3 (3.7 mL, 1M in dichloromethane) was added dropwise at −10° C. under nitrogen. Stirring was continued at −10° C. for 50 min., then at room temperature for 45 min. Water was added to quench the reaction. The dichloromethane layer was set aside. The aqueous layer was adjusted to pH 8 with sodium bicarbonate and extracted with 30% isopropanol in chloroform 4 times. The dichloromethane layer was washed with brine and the brine layer was adjusted to pH 8 with sodium bicarbonate and extracted with 30% isopropanol in chloroform 1 times. The combined 30% isopropanol in chloroform extracts were dried and concentrated to give 222 mg of E3 as a solid, which was used directly for next step.
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