4 pagesInternational audienceWe have developed a tandem conjugate addition-elimination sequence for the diastereoselective synthesis of protected allylic syn 1,3-diols, starting from vinyl sulfones. The sulfonyl group was then reduced with sodium amalgam to furnish the E olefin as the major isomer. This method was applied to the synthesis of a trisubstituted alkene modeling the C21-C25 fragment of Dolabelide C