N,N-Dialkyl-N′-Chlorosulfonyl Chloroformamidines in Heterocyclic Synthesis. Part XIV.* Synthesis and Reactivity of the New Benzo[4,5]imidazo[1,2-b][1,2,6]thiadiazine Ring System

N,N-Dialkyl-N'-chlorosulfonyl chloroformamidines 1 underwent regioselective reactions with the 1,3-NCCbis-nucleophilic 1H-benzimidazole-2-acetonitriles 4 and related compounds to produce benzo[4,5]imidazo[1,2-b][1,2,6]thiadiazine dioxides 6, 9, 12, and 14, representatives of a new ring system. Reaction of dichlorides 1 with trifluoroacetyl derivative 16 afforded benzo[4,5]imidazo[1,2-c]pyrimidines 19 and 20. An N-acyl and some N-alkyl derivatives of benzimidazo-thiadiazines 6 were prepared to demonstrate the potential of this new ring system as a novel scaffold for synthetic and medicinal chemistry applications. Treatment of the 4-cyano-5-methyl-benzimidazo-thiadiazine 26c with LiAlH4 resulted in an unexpected and remarkable conversion of the nitrile to give the 4,5-dimethyl-benzimidazo-thiadiazine 29.