Photoisomerization of sultams derived from saccharin; Part 4: Generation of cyclic sulfine hydroxamic acids

Various areno[d]annulated 3-mono- and 3,3-disubstituted 2,3-dihydro-[1,2]be nzisothiazole 1,1-dioxides undergo a facile rearrangement into the correspo nding 2,3-dihydro-2-hydroxy[1,2]benzisothiazole 1-oxides upon irradiation a t 254 nm in methanol. The latter represent a new, but labile functional gro up, i.e. the cyclic version of the sulfine hydroxamic acid. When C-3 in the starting materials is substituted by one methyl or phenyl only, that photo isomer is formed preferentially which has the sulfoxide O atom in an anti-o rientation to the said substituent. 2-Alkoxymethyl substituted starting mat erials show the same type of formal oxygen shift. The structures of all pho toproducts have been assigned largely from H-1 NMR data and unambiguously c orroborated by X-ray crystal structure analyses of two photoproducts.