| Abstract
| - The reaction of singlet oxygen with variously substituted oxathiins 1 affords dicarbonyl compounds4 and/or ketosulfoxides 7 and 8 depending on the nature of the substituent at C3 and on the reactionconditions. The normal fragmentation of dioxetanes 2 to 4 competes with an intramolecular oxygentransfer to ring sulfur, which leads to 7 and 8, presumably via the labile epoxides 5. This newpathway is promoted by electron-withdrawing groups at C3 and, for unsubstituted and monosubstituted amide derivatives 1h and 1i, respectively, by the solvent basicity. Chemical experimentssupport the intermediacy of epoxides 5 for 7, whereas they are not conclusive for 8. However, theformation of the latter compounds appears to be favored by polar solvents and cation-stabilizinggroups at C2 as phenyl or methyl, and these observations may be well accounted for by the suggestedpathway from 5 through charged species as E. Direct oxidation by singlet oxygen to sulfur isunsignificant, except for the amide series and for 1g or when the oxygenation is carried out inmethanol.
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