Chlorination of 2, 1-benzisothiazoline 2, 2-dioxides (benzosultams) with hexachloroethane under phase-transfer catalysis condition in the presence of 50% aqueous NaOH and tetraalkylammonium salt gives 3, 3-dichlorobenzosultams in good yields. Thermal extrusion of SO2 from 3, 3-dichloropyridosultams generates dichloro derivatives of aza-ortho- xylylenes which do not enter [4+ 2] cycloaddition reactions, but add amines to form ...