The SRN1 reactivity of halobenzenesulfonamides and related compounds

An investigation of the application of nucleophilic aromatic substitution by the SRN 1 mechanism of halobenzenesulfonamides and related compounds towards the synthesis of 1,2-benzothiazine I,I-dioxides is reported. 3-Substituted and 3,4- disubstituted 2H-l,2-benzothiazine l,l-dioxides were prepared in moderate to good yields via the photostimulated reaction of 2-halobenzenesulfonamides with ketone enolates. It was observed that with certain ketone enolates reduction to yield benzene sulfonamide competed with the substitution reaction. The presence of β-hydrogen atoms was a common structural feature of ketones used in reactions in which reduction competed with substitution. It was also observed that the amount of reduction product isolated increased as a function of the number of β-hydrogen atoms present on the ketone enolate. It was found that 2-bromo and 2-iodobenzenesulfonamide exhibit comparable reactivity with ketone enolates that do not possess β-hydrogen atoms. However, a marked decrease in the reactivity of 2-bromobenzenesulfonamide was observed when β-hydrogen atoms were present on the ketone enolate.