Lewis-Acid-Promoted Divergent Synthesis of Cyclopentenes and Butanolides from Allyl Sulfides and Electron-Deficient Alkynes

A Lewis-acid-promoted cascade reaction between allyl sulfides and electron-deficient alkynes has been developed for the synthesis of cyclopentenes and butanolides under mild Lewis acidic conditions. The transformation proceeds through thia-Michael addition followed by a [3,3]-sigmatropic rearrangement and intramolecular cyclization. The nature of the ester substituent on the allyl sulfide governs pathway divergence, selectively producing either cyclopentenes through all-carbon cyclization or butanolides via oxa-cyclization with excellent diastereoselectivity.