[CH2:1]([O:3][C:4](=[O:23])[CH2:5][NH:6][C:7]([C:9]1[C:10](=[O:22])[S:11][C:12]2[C:17]([C:18]=1[OH:19])=[CH:16][C:15]([Cl:20])=[CH:14][C:13]=2Br)=[O:8])[CH3:2].[CH3:24][Sn](C)(C)C>CN(C)C=O.C(OCC)(=O)C>[CH2:1]([O:3][C:4](=[O:23])[CH2:5][NH:6][C:7]([C:9]1[C:10](=[O:22])[S:11][C:12]2[C:17]([C:18]=1[OH:19])=[CH:16][C:15]([Cl:20])=[CH:14][C:13]=2[CH3:24])=[O:8])[CH3:2][(8-Bromo-6-chloro-4-hydroxy-2-oxo-2H-thiochromene-3-carbonyl)-amino]-acetic acid ethyl ester (500 mg, 1.19 mmol) was dissolved in anhydrous N,N-dimethylformamide (4 mL). Tetramethyl tin (247 μL, 1.783 mmol), dichloro(bis-triphenylphosphino) palladium (125 mg, 0.18 mmol), and 4 angstrom molecular sieves were added sequentially to the reaction. The reaction was sealed and heated to 120° C. in an oil bath for 45 min. The reaction was cooled, diluted with ethyl acetate, and partitioned with water. The organic phase was washed with water, brine, and dried over sodium sulfate. The crude material was purified by silica gel chromatography (15%-45% ethyl acetate in hexanes) to provide [(6-chloro-4-hydroxy-8-methyl-2-oxo-2H-thiochromene-3-carbonyl)-amino]-acetic acid ethyl ester (400 mg, 95%). MS ESI(−) m/e: 354.223 (M−1).
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