[CH2:1]([O:3][C:4]([CH2:6][C:7]1[NH:8][S:9](=[O:18])(=[O:17])[C:10]2[CH:16]=[CH:15][S:14][C:11]=2[C:12]=1[OH:13])=[O:5])[CH3:2].[H-].[Na+].[CH3:21]I>CN(C)C=O>[CH2:1]([O:3][C:4]([CH2:6][C:7]1[N:8]([CH3:21])[S:9](=[O:17])(=[O:18])[C:10]2[CH:16]=[CH:15][S:14][C:11]=2[C:12]=1[OH:13])=[O:5])[CH3:2]1.93 G. (7 mmol) of 3-ethoxycarbonylmethyl-4-hydroxy-2H-thieno[2,3-e]-1,2-thiazine 1,1-dioxide are dissolved in 4 ml. of absolute dimethylformamide and added dropwise during 30 minutes at 0° C. to a stirred suspension of 0.185 g. (7.7 mmol) of sodium hydride in 2 ml. of absolute dimethylformamide. The mixture is stirred for a further 1 hour at room temperature. There are then added firstly 0.53 ml. (1.2 g.; 8.45 mmol) of methyl iodide and, after 30 minutes, a further 0.25 ml. (0.565 g; 4 mmol) of methyl iodide and the mixture is allowed to react for 1 hour. After distillation of the solvent, the residue is taken up in 30 ml. of 0.5-N hydrochloric acid and 30 ml. of methylene chloride, the organic phase is separated and the aqueous layer is back-extracted twice with a small amount of methylene chloride. The combined organic extracts are dried over sodium sulfate and evaporated. The crystalline residue is digested with a small amount of cold ethanol. There is obtained 3-ethoxycarbonylmethyl-4-hydroxy-2-methyl-2H-thieno[2,3-e]-1,2-thiazine 1,1-dioxide of melting point 161°-163° C. (crystal transformation at 151°-152° C).
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