[CH3:1][CH:2]1[CH2:7][C:6]2[CH:8]=[CH:9][CH:10]=[C:11]([S:12]([NH2:15])(=[O:14])=[O:13])[C:5]=2[O:4][S:3]1(=[O:17])=[O:16].[CH3:18][N:19]=[C:20]=[O:21].N12CCCN=C1CCCCC2>C(#N)C.O>[CH3:1][CH:2]1[CH2:7][C:6]2[CH:8]=[CH:9][CH:10]=[C:11]([S:12]([NH:15][C:20]([NH:19][CH3:18])=[O:21])(=[O:14])=[O:13])[C:5]=2[O:4][S:3]1(=[O:17])=[O:16]A solution of 24.96 g of 3,4-dihydro-3-methyl-2,2-dioxo-1,2-benzoxathiin-8-ylsulfonamide in 120 ml of absolute acetonitrile is cooled to +8° C. After the addition of 6 ml of methyl isocyanate, a solution of 13.4 ml of 1,8-diazabicyclo[5.4.0]undec-7-ene in 15 ml of acetonitrile is added dropwise over 15 minutes at 10° C. The reaction mixture is stirred for a further hour at room temperature. The mixture is subsequently diluted with 180 ml of water. The product is precipitated by the dropwise addition of 48 ml of 2N hydrochloric acid. The precipitate is isolated and dried, affording 26.4 g of N-(3,4-dihydro-3-methyl-2,2-dioxo-1,2-benzoxathiin-8-ylsulfonyl)-N'-methylurea with a melting point of 235°-238° C.
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