[CH2:1]([N:3]1[C:7](=[O:8])[C:6](O)=[C:5]([C:10]2[CH:15]=[CH:14][CH:13]=[CH:12][CH:11]=2)[S:4]1(=[O:17])=[O:16])[CH3:2].CN(C=O)C.C(Cl)(=O)C([Cl:26])=O>C(Cl)Cl>[Cl:26][C:6]1[C:7](=[O:8])[N:3]([CH2:1][CH3:2])[S:4](=[O:17])(=[O:16])[C:5]=1[C:10]1[CH:15]=[CH:14][CH:13]=[CH:12][CH:11]=12-Ethyl-4-hydroxy-5-phenylisothiazol-3(2H)-one 1,1-dioxide (5 g, 19.76 mmol) was dissolved in dry DCM (250 mL) and cooled to 0° C. under N2. Dry DMF (15 mL) was added, followed by oxalyl chloride (3 mL, 34.4 mmol). The ice-bath was removed and the mixture was refluxed at 50° C. under N2 for 4 h. The reaction mixture was evaporated and the residue was diluted with EtOAc and washed with water (3×25 mL) and brine, dried over Na2SO4 and evaporated. Another (16 g, 63.24 mmol) of 2-ethyl-4-hydroxy-5-phenylisothiazol-3(2H)-one 1,1-dioxide was dissolved in dry DCM (500 mL) and cooled to 0° C. under N2. Dry DMF (20 mL) was added followed by oxalyl chloride (9 mL, 103.2 mmol). The ice-bath was removed and the mixture was refluxed at 50° C. under N2 for 4 h. The reaction mixture was evaporated and the residue was diluted with EtOAc and washed with water (3×50 mL) and brine, dried over Na2SO4 and evaporated where by red solid was obtained. The crude material from both batches were combined and purified by column chromatography on silica gel using 2.5-3% EtOAc in petroleum ether as eluant, and recrystallised from MeOH to give the title compound (15.7 g, 70%) as a white solid; 1H NMR (400 MHz, CD3OD) δ 1.42 (t, 3H, J=7.3 Hz), 3.84 (q, 2H, J=7.3 Hz), 7.6-7.7 (m, 3H), 7.9-8.0 (m, 2H); Mass Spectrum: M+H+ 272.
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