[O:1]1[CH2:6][CH2:5][NH:4][C:3]2[CH:7]=[CH:8][C:9]([S:11](Cl)(=[O:13])=[O:12])=[CH:10][C:2]1=2.[S:15]1[C:19]([NH2:20])=[N:18][CH:17]=[N:16]1.C1COCC1.[OH-].[Na+]>Cl>[S:15]1[C:19]([NH:20][S:11]([C:9]2[CH:8]=[CH:7][C:3]3[NH:4][CH2:5][CH2:6][O:1][C:2]=3[CH:10]=2)(=[O:13])=[O:12])=[N:18][CH:17]=[N:16]1A vial was charged with 3,4-dihydro-2H-benzo[b][1,4]oxazine-7-sulfonyl chloride (from HangZhou Trylead Chemical, Hangzhou, China) (74.42 mg, 0.318 mmol), 1,2,4-thiadiazol-5-amine (70.9 mg, 0.701 mmol), and THF (1991 μL) to give a cloudy solution. The vial was cooled in an ice-bath for 5 min, then sodium hydroxide (6N aq.) (117 μL, 0.701 mmol) was added dropwise. After 45 min, the mixture was allowed to warm to room temperature with the bath. The mixture was diluted with 1N aq. HCl and extracted with EtOAc (3×). The combined organic extracts were dried over sodium sulfate, filtered, and concentrated. The residue was purified by chromatography on silica gel (4% MeOH/DCM). Several mixed fractions at the tail end of the elution were discarded, and the remainder that contained product were combined and concentrated to give N-(1,2,4-thiadiazol-5-yl)-3,4-dihydro-2H-benzo[b][1,4]oxazine-7-sulfonamide (33.19 mg, 0.111 mmol) as a white foam. m/z (ESI) 299.2 (M+H)+.
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