CS(C)=O.C(Cl)(=O)C(Cl)=O.[N:11]1[S:12][CH:13]=[C:14]2[C:19]([CH2:20][OH:21])=[CH:18][CH:17]=[CH:16][C:15]=12.C(N(CC)CC)C>ClCCl>[N:11]1[S:12][CH:13]=[C:14]2[C:19]([CH:20]=[O:21])=[CH:18][CH:17]=[CH:16][C:15]=12Under nitrogen atmosphere, dimethyl sulfoxide (10.8 mL, 153 mmol) was added to a solution of oxalyl chloride (6.68 mL, 76.0 mmol) in dichloromethane (200 mL) at −78° C., and the mixture was stirred for 30 min. To the reaction mixture was added a solution of 2,1-benzisothiazol-4-ylmethanol (4.20 g, 25.4 mmol) in dichloromethane (54 mL), and the mixture was stirred for 2 hr. To the reaction mixture was added triethylamine (32.2 mL, 229 mmol) at −78° C., and the mixture was stirred for 1 hr. The solvent was evaporated under reduced pressure. The residue was purified by silica gel column chromatography (ethyl acetate/hexane=20/80) to give the title compound (3.94 g, yield 95%).
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