Synthesis of 3‑Sulfenylated Coumarins: BF3·Et2O‑Mediated Electrophilic Cyclization of Aryl Alkynoates Using N‑Sulfanylsuccinimides

A simple and efficient metal-free sulfenylation/​cyclization of aryl alkynoates has been developed, obtaining various 3-sulfenylated coumarins in moderate to excellent yields. In the presence of BF3·​Et2O, the stable and readily accessible N-sulfanyl­succinimides were employed as electrophiles to induce the 6-endo-dig electrophilic cyclization of alkynoates. The reaction using substrates bearing a methoxy group on the phenoxy ring proceeded in an exclusively distinct pathway via either ipso sulfenyl­cyclization or sulfenylation of the phenoxy ring depending on the different locations of the methoxy substituent. The resulting 3-sulfenylated coumarins can be readily transformed to 3-sulfinylated or 3-sulfonylated coumarins under different oxidation conditions.