6.1 Thiol–Ene/Yne Click Reactions: A Powerful Tool Toward Diversity-Oriented Synthesis

The clickable addition reaction between thiols and unsaturated compounds leading to the generation of (branched/linear) thioethers or (branched/linear) vinyl sulfides is known as the hydrothiolation reaction. Based upon the nature of unsaturation, i.e. double bond or triple bond, hydrothiolation reactions are classified as thiol–ene and thiol–yne click reactions, respectively. These reactions have emerged as a powerful and widely used strategy for the generation of carbon–sulfur bonds due to several associated benefits including versatile synthetic procedures, wide functional-group tolerance, high atom economy with few to no byproducts, and simple purification. The hydrothiolation reactions have numerous trapping applications in the fields of polymer chemistry, nanoengineering, pharmaceuticals, natural products, and perhaps most importantly in medicinal chemistry for the synthesis of many drugs and bioactive molecules.