C[O:2][C:3]1[C:8]2[N:9]=[CH:10][S:11][C:7]=2[CH:6]=[C:5]([C:12]([O:14][CH3:15])=[O:13])[CH:4]=1.B(Br)(Br)Br>C(Cl)Cl>[OH:2][C:3]1[C:8]2[N:9]=[CH:10][S:11][C:7]=2[CH:6]=[C:5]([C:12]([O:14][CH3:15])=[O:13])[CH:4]=1To a stirred solution of methyl 4-methoxy-1,3-benzothiazole-6-carboxylate (20.0 g, 0.0897 mol) in anhydrous CH2Cl2 (300 mL) was added drop wise BBr3 (112.5 g, 0.448 mol) at −78° C. Then the resulting mixture was stirred at −78° C. for 3 hours and allowed to warm to room temperature overnight. TLC (EtOAc/Petroleum ether 1:4) showed the reaction was complete. The reaction mixture was concentrated in vacuum and methanol (100 mL) was added drop wise to the residue. Then the mixture was concentrated again in vacuum. The residue was washed with water and recrystallized from methanol to afford the desired product (12 g, 64%) as a white solid. 1H NMR (400 MHz, CDCl3): δ 10.671 (s, 1H), 9.437 (s, 1H), 8.252-8.248 (s, 1H), 7.488-7.484 (s, 1H), 3.898 (s, 3H).
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