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.