Abstract Reaction of o-azidobenzenesulfonamides with ethyl carbonochloridate afforded the corresponding amide derivatives, which gave 3-ethoxy-1, 2, 4-benzothiadiazine 1, 1- dioxides through an intramolecular aza-Wittig reaction. The reaction was found to be general through the synthesis of a number of benzothiadiazine 1, 1-dioxides. Acid-catalyzed hydrolysis of 3-ethoxy-1, 2, 4-benzothiadiazine 1, 1-dioxides furnished the 2-substituted ...