The Reactions of O2(1Δg) with Anancomeric 1,3-Dithianes. The First Experimental Evidence in Support of a Hydroperoxy Sulfonium Ylide as a Precursor to Sulfoxide on the Sulfide Singlet Oxygen Reaction Surface

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Abstract
The kinetic isotope effects for the formation of anancomeric 1,3-dithiane-1-oxides in the reactions of singlet oxygen with the parent 1,3-dithianes have been determined for a series of 2-protio and 2-deuterio analogues. The substantial isotope effects are used to argue for formation of a hydroperoxysulfonium ylide as a key intermediate in sulfoxide formation. These results confirm an earlier theoretical prediction and force a change in the currently accepted mechanism for this important reaction. The first experimental demonstration of a novel singlet oxygen-induced epimerization of a 1,3-dithiane and a novel intramolecular electron transfer within a hydroperoxysulfonium ylide are also reported.