N,N-dialkyl-N′-chlorosulfonyl chloroformamidines 1 were treated with 2-aminobenzimidazoles 2 to give [1,2,4,6]thiatriazino[2,3-a]benzimidazole 1,1-dioxides 3 and [1,2,4,6]thiatriazino[4,3-a]benzimidazole 2,2-dioxides 4. Some N-alkyl-, N-acyl-, and N-sulfonyl-derivatives of 3 were prepared. These products are derivatives of rare heterocycles.