[CH3:1][O:2][C:3]([C:5]1[S:9][C:8]2[CH:10]=[C:11]([O:14][CH3:15])[CH:12]=[CH:13][C:7]=2[CH:6]=1)=[O:4].B(Br)(Br)Br.C([O-])([O-])=O.[Cs+].[Cs+].ClC1[S:28][C:29]2[CH:35]=[CH:34][CH:33]=[CH:32][C:30]=2[N:31]=1.Cl>C(Cl)Cl.CCOC(C)=O.O>[CH3:1][O:2][C:3]([C:5]1[S:9][C:8]2[CH:10]=[C:11]([O:14][C:15]3[S:28][C:29]4[CH:35]=[CH:34][CH:33]=[CH:32][C:30]=4[N:31]=3)[CH:12]=[CH:13][C:7]=2[CH:6]=1)=[O:4]To a cooled (−78° C.) solution of 6-methoxy-benzo[b]thiophene-2-carboxylic acid methyl ester (4.7 g, 21 mmol) in DCM (210 mL) was added BBr3 (6.0 mL, 15.9 g, 63 mmol) dropwise and the reaction mixture was allowed to warm (rt, 4 h). The reaction mixture was cooled (0° C.), diluted with EtOAc (200 mL) and treated with H2O (25 mL). The organic layer was separated and the aqueous layer was extracted with EtOAc (2×100 mL). The organic layer was dried, filtered and concentrated in vacuo. The resulting residue was dissolved in MeCN (150 mL) and treated with Cs2CO3 (9.8 g, 30 mmol) and 2-chlorobenzothiazole (1.9 mL, 2.5 g, 15 mmol) and the reaction mixture was heated (60° C., 4 h). The reaction mixture was cooled (rt) and treated with 1 M HCl (50 mL) and partitioned between EtOAc (100 mL) and H2O (50 mL). The organic layer was separated and the aqueous layer was extracted with EtOAc (2×100 mL). The organic layer was dried, filtered and concentrated in vacuo. The resulting residue was purified by silica gel flash chromatography using EtOAc:hexane (0-60%) to provide the title compound as a colorless foam (0.27 g, 5%). MS (ESI): mass calcd. for O11H10O3S2, 341.0; m/z found, 342.0 [M+H]+. 1H NMR (400 MHz, CDCl3): 8.07 (s, J=0.6, 1H), 7.93 (dd, J=5.4, 3.2, 2H), 7.75 (dd, J=8.1, 0.6, 1H), 7.70 (dd, J=8.0, 0.7, 1H), 7.50-7.37 (m, 2H), 7.35-7.27 (m, 1H), 3.96 (s, 3H).
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