Regioselectivity in the ring opening of epoxides: A metal-free cascade C-S/C-O bond formation approach to 1,3-oxathiolan-2-ylidenes through heteroannulation of α-enolic dithioesters at room temperature

Abstract

An operationally simple and efficient approach to hitherto unreported and synthetically demanding 1,3-oxathiolan-2-ylidenes has been developed. The approach involves a cascade [2+3] heteroannulation of α-enolic dithioesters with epoxides promoted by non-nucleophilic moderate base Cs 2CO3 at room temperature. Typical features of this strategy include metal-free mild reaction conditions, atom-economy, high yields, and efficacy of forming two consecutive C-S and C-O bonds, and one ring in a single stroke. MeSH is the only by-product, and the stereochemistry of the exocyclic α-oxoketene moiety of 1,3-oxathiolane was assigned to have Z-configuration. © Georg Thieme Verlag Stuttgart New York.