Br[C:2]1[CH:3]=[C:4]([S:15]([NH2:18])(=[O:17])=[O:16])[C:5]2[O:10][S:9](=[O:12])(=[O:11])[C:8]([CH3:13])=[CH:7][C:6]=2[CH:14]=1.[H][H].C(N(CC)CC)C>O1CCCC1.[Pd]>[O:12]=[S:9]1(=[O:11])[C:8]([CH3:13])=[CH:7][C:6]2[CH:14]=[CH:2][CH:3]=[C:4]([S:15]([NH2:18])(=[O:16])=[O:17])[C:5]=2[O:10]1
120 g of 6-bromo-2,2-dioxo-3-methyl-1,2-benzoxathiin-8-ylsulfonamide are dissolved in 2.4 liters of tetrahydrofuran and the solution is hydrogenated with hydrogen for 40 minutes, in the presence of 41.3 g of triethylamine and 12.0 g of 5% palladium on carbon catalyst, under normal pressure and in the temperature range from 20° to 25° C. The mixture is filtered, the filtrate is concentrated, and the residue is taken up in 1300 ml of hot 90% aqueous ethanol. The insoluble constituents are separated and the solution is cooled to 0° C. The precipitate is separated and dried, affording 70 g of 2,2-dioxo-3-methyl-1,2-benzoxathiin-8-ylsulfonamide of m.p. 204°-205° C.
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