The surprising photochemistry of sultams related to saccharin

摘要

The known light induced reactions of sulfonamides and sultams are in most (but not all) casesinitiated by S–N homolysis. Sulfur dioxide release may be a consequence of this primary process. In theauthor's laboratory three hitherto unexplored photoreactions of saccharin-derived sultams have been investigated:(i) a novel formal oxygen shift from sulfur to nitrogen generating upto now unknown cyclicN-hydroxysulfinamides; (ii) a condensative dimerization of 2,3-dihydro-1,2- benzoisothiazole 1,1-dioxidegenerating a new cleft molecule, and (iii) a facile allylic skeletal rearrangement of a pyrrolo-anellated dihydro-1,2-benzoisothiazole. At least in the latter two cases an initial S–N-homolysis seems to be vital for the processesobserved, whereas in the first case some ambiguity remains with respect to the first step. Scope andlimitations are discussed and rationales for the conversions observed are presented, with special emphasison structure proof by X-ray crystal structure determinations. All reactions discussed have to be treatedwithin the wider context of current sulfonamide and sultam photochemistry.