Dihydro-1,4-thiazine 1,1-dioxides synthesis

H,3 H-Oxazolo[4,3-c][ 1,4]thiazine-6-carboxylic acid, 8,8a-dihydro-3,3-dimethyl-methyl ester X-ray diffraction, 6, 647 Oxazolo[2,3-h]thiazol-3(2H) -one 1,1-dioxide synthesis, 6, 1005... 

Similar ring systems were prepared <97JHC1693> by Coppo and Fawzi from the reaction of substituted ethyl 5-[methyl(methylsulfonyl)amino]-l 7/-pyrazole-4-carboxylates 119 with sodium hydride. This gave the 7-substitued 1,7-dihydro-l-methylpyrazolo[3,4-c][l, 2]thiazin-4(37/)-one 2,2-dioxides 120 in fair to good yield (Scheme 30). They also extended this synthesis by treating methyl 2-[methyl(methylsulfonyl)amino]-6-(trifluoromethyl)-3-pyridinecarboxylate 121 with sodium hydride in dimethylformamide to yield l-methyl-7-(trifhioromethyl)-l//-pyrido[2,3-c][l,2]thiazin-4(3//)-one 2,2-dioxide 122 in 79% yield (Scheme 31) <98JHC499>. 

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