Synthesis of pyrazolo[3,4- c ][1,2]thiazin-4(3 H )-one 2,2-dioxides, new heterocycles

The reaction of substituted ethyl 5-aminopyrazole-4-carboxylates with two equivalents of methanesulfonyl chloride gave the substituted ethyl 5-[bis(methylsufonyl)amino]-1H-pyrazole-4-carboxylates II. Removal of one of the methanesulfonyl groups, followed by alkylation of the ethyl 5-[(methylsulfonyl)amino]-1H-pyrazole-4-carboxylates III with methyl iodide produced the substituted ethyl 5-[methyl(methylsulfonyl)amino]-1H-pyrazole-4-carboxylates IV. Treatment of IV with sodium hydride gave the 7-substituted 1,7-dihydro-1-methylpyrazolo[3,4-c][1,2]thiazin-4(3H)-one 2,2-dioxides V.