Hydrochloric Acid → 2H-Thieno(2,3-e)-1,2-thiazine-3-carboxylic acid, 4-hydroxy-2-methyl-, methyl ester, 1,1-dioxide

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Reaktionsschritte

13.2 G. (0.041 mol) of the obtained 3-(N-carbethoxymethyl-N-methylsulfamoyl)-thiophene-2-carboxylic acid methyl ester are suspended in 42 ml. of a 1-N methanolic sodium methylate solution in the cold and under a nitrogen atmosphere, everything dissolving after stirring for 15 minutes. The solution is heated to reflux for 25 minutes, cooled, neutralized with concentrated hydrochloric acid and evaporated in vacuo. The residue is taken up in methylene chloride, shaken out once each time with water and a 5% sodium bicarbonate solution, dried and evaporated. The crystalline residue is digested with a small amount of methanol for purification. There is obtained 4-hydroxy-3-methoxycarbonyl-2-methyl-2H-thieno[2,3-e]-1,2-thiazine 1,1-dioxide of melting point 193°-195° C., which can be converted by reaction with 2-aminothiazole in a manner analogous to that described in the last part of Example 1 into the 4-hydroxy-2-methyl-N-(2-thiazolyl)-2H-thieno[2,3-e]-1,2-thiazine-3-carboxamide 1,1-dioxide of melting point 217° C. (decomposition).

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