The SC, SN, and NC bonds in the five‐membered ring do not undergo cleavage when the sulfonamide 1 is irradiated. Instead, the sulfinehydroxamic acid 2 is formed, which is stable in crystalline form but isomerizes back to 1 in solution. An intermolecular hydrogen bond is of critical importance for the stability of crystalline 2.

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Various areno[d]annulated 3-mono-and 3,3-disubstituted 2,3-dihydro-[1,2]benzisothiazole 1,1-dioxides undergo a facile rearrangement into the corresponding 2,3-dihydro-2-hydroxy-[1,2]benzisothiazole 1-oxides upon irradiation at 254 nm in methanol. The latter represent a new, but labile functional group, 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 photoisomer is formed preferentially which has the sulfoxide O atom in an anti-orientation to the said substituent. 2-Alkoxymethyl substituted starting materials show the same type of formal oxygen shift. The structures of all photoproducts have been assigned largely from 1 H NMR data and unambiguously corroborated by X-ray crystal structure analyses of two photoproducts.

A 2 I-coz MEOH/HCL i o CO Me Me02C-4 JI 0 [**I Schwefelverbindungen, 106. Mitteilung. Diese Arbeit wurde von der Deutschen Forschungsgemeinschaft und vom Fonds der Chemischen lndustrie gefbrdert. -105. Mitteilung: R. Steudel, D. Jensen, B. Plinke, Z. Naturforsch.. im Druck. Angew. Chem. 99 (1987) Nr. 2 0 VCH Verlagsgesellschaji mbH. 0-6940 Weinheim. 1987 W44-8249/87/0202-0143 $ 0 2 . 5 0~~

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