Synthesis of Diazaheterocyclic Ring-Fused 1,2,4-Benzothiadiazine 1,1-Dioxides by a Sequential Aza-Wittig/NH-Addition Cyclization/Nucleophilic Ring-Closure Methodology withN-Alkenyl-2-carbodiimidobenzenesulfonamides as Key Intermediates
iminophosphoranes to aza-Wittig reactions with isocyanates generated functionalized carbodiimides, which spontaneously underwent cyclization to form 2-alkenyl-3-(R2-substituted amino)-2H-1,2,4-benzothiadiazine 1,1-dioxides by internal nucleophilic addition. Subsequent (tandem) cyclizations through iodoamination or hydroamination with HgII/NaBH4 produced a variety of diazaheterocyclicring-fused benzothiadiazine