Abstract:

Preparation of olefins with a rigorous regio- and stereochemical control is of great interest. Many protocols leading to vinyl chalcogenides are described in the literature. The most frequently employed method for preparation of (Z)-vinyl chalcogenides (anti-Markovnikov isomer) is the hydrochalcogenation of terminal and internal alkynes using nucleophilic organyl chalcogenolate anions, generated in situ from diorganyl dichalcogenide in the presence of a reducting agent (as NaBH4, Li, Sn, Cu, In and Zn) or from elemental chalcogen in the presence of alkyl lithium. On the other hand, Markovnikov regioisomers can be achieved by adding PhSeBr to terminal olefins under rigid kinetic conditions (-78°C) followed by the dehydrohalogenation. Nevertheless, anti- Markovnikov E and Z stereoisomers adduct were obtained at high temperatures. In this study, we describe a new chemo- regio and stereoselective hydrochalcogenation of terminal alkynols mediated by zinc organyl chalcogenolate generated in situ, affording preferentially Markovnikov adducts in mild reaction conditions (Scheme 1).