Stereoselective Synthesis of Z -Styryl Sulfides from Nucleophilic Addition of Arylacetylenes and Benzyl Thiols.

The stereoselective synthesis of Z-anti -Markovnikov styryl sulfides via an anionic thiolate-alkyne addition reaction was achieved when the terminal alkynes and benzyl mercaptans were reacted using t BuOLi (0.5 equiv) in EtOH under ambient conditions. Exclusive stereoselectivity (ca. 100%) was achieved by stereoelectronic control via anti -periplanar and anti -Markovnikov addition of benzylthiolates to phenylacetylenes. Solvolysis of lithium thiolate ion pairs in ethanol significantly suppresses the competing formation of the E- isomer. A remarkable enhancement of the Z -selectivity under a longer reaction time was observed.