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.
Gopalakrishnan et al. (Fri,) studied this question.