Abstract: The first examples of sulfene formation by thermal rearrangement of allyl vinyl sulfones-the" sulfo-Cope" rearrangement-are described. In ethanol-pyridine solution the N- ethylpyridinium salt of the corresponding sulfonic acid is ob-tained in good yields (70-95%); the reaction is therefore a potentially useful process for making a new carbon-carbon bond. The rearrangement takes place also on flash thermolysis to give a poor yield of the ...