[F:1][C:2]1[C:10]2[S:9][CH:8]=[N:7][C:6]=2[CH:5]=[CH:4][CH:3]=1.[Cl:11][S:12](O)(=[O:14])=[O:13]>>[F:1][C:2]1[CH:3]=[CH:4][C:5]([S:12]([Cl:11])(=[O:14])=[O:13])=[C:6]2[C:10]=1[S:9][CH:8]=[N:7]27-fluorobenzo[d]thiazole 25D (500 mg, 3.26 mmol) was added dropwise to chlorosulfonic acid (2.5 mmol) at 0° C. After the addition was complete, the mixture was stirred at room temperature for 0.5 h and then heated at 105° C. and stirred overnight. The resulting mixture was cooled to −10° C. and quenched by pouring on crushed ice slowly. The resulting mixture was extracted with EtOAc (20 mL×2). The combined organic phase was washed with brine, dried over anhy. Na2SO4 and concentrated in vacuo. Column chromatography (15% PE/EtOAc) afforded 200 mg of title compound. 1H NMR (CHLOROFORM-d) δ: 9.44 (s, 1H), 8.32 (dd, J=8.6, 4.6 Hz, 1H), 7.38 (t, J=8.5 Hz, 1H).
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