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

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