Synthesis of Diazaheterocyclic Ring‐Fused 1,2,4‐Benzothiadiazine 1,1‐Dioxides by a Sequential Aza‐Wittig/NH‐Addition Cyclization/Nucleophilic Ring‐Closure Methodology with N‐Alkenyl‐2‐carbodiimidobenzenesulfonamides as Key Intermediates

Treatment of N‐alkenyl‐2‐azidobenzenesulfonamides with triphenylphosphane and subsequent subjection of the resulting 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 diazaheterocyclic ring‐fused benzothiadiazine dioxides. In one case a methano‐bridged benzothiatriazabicyclotridecanone was obtained. The scope and limitations of these cyclizations are reported. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)