Intramolecular sulphonyl-amidomethylation. Part I. Cyclization of benzylsulphonamides

Cyclization of benzylsulphonamides with aldehydes in strong acid media is a synthetically useful route to 3,4-dihydro-1H-2,3-benzothiazine 2,2-dioxides III. With insufficient acid strength or reaction time, kinetic products IV and VI are obtained; the latter compounds can be converted into the thermodynamic products III under stronger conditions. The reactions proceed via imine VII or iminium VIII compounds as common intermediates.