Abstract
Alkyne hydrothiolation – that is, the addition of the SH bond of a thiol across the carbon-carbon triple bond of an unactivated alkyne – belongs to the ample class of hydrofunctionalization reactions whose main feature is their occurrence with total atom economy. Hence this reaction is emerging as a valuable tool for the preparation of sulfur-containing compounds such as vinyl thioethers, which are of interest for their own biological properties and for their use as intermediates in total synthesis. Thus, the first part of this review deals with the various efforts directed towards the preparation of vinyl thioethers in a regio- and diastereoselective manner by metal-catalyzed approaches in recent years. The number of methods employed, with use of a variety of catalysts and reaction conditions, allow the synthesis of vinyl thioethers to be carried out with high efficiency and selectivity. The second part of the article is based on the use of the photoinduced free-radical approach to hydrothiolation, which allows the introduction of two thiol fragments across the carbon-carbon triple bond, thereby leading to the formation of dithioethers. This approach turned out to be especially useful as a ligation tool for the installation of densely functionalized arrays on various scaffolds and complex biomolecular systems. Concluding remarks emphasize the role of the photoinduced free-radical strategy as a complementary tool to copper-catalyzed azide-alkyne cycloaddition.