Transition Metal-Catalyzed Cascade C-H Activation/Cyclization with Alkynes: An Update on Sulfur-Containing Directing Group

In light of the extensive applications of sulfur-containing heterocyclic compounds in drug discovery, agrochemicals, and advanced materials, the construction of complex sulfur-containing molecular scaffolds has flourished in recent years. There is a profound interest in synthetic methods for forming carbon-sulfur bonds. Regarding this, transition metal (TM)-catalyzed C-H bond activation has emerged as a valuable means for the rapid formation of C-S bonds, although it is comparatively less explored than C-N or C-C bonds. The research significance of sulfur-directed C-H activation chemistry lies in maintaining a balance between activating and poisoning the catalyst as well as in the diversity and novelty of its properties. This review centers on sulfur-directed TM-catalyzed cascade C-H activation/cyclization with alkyne and encompasses the literature mainly from 2012 to 2024. The widely acknowledged reactivity and versatility of rhodium, ruthenium, and cobalt catalysts have given rise to various captivating cascade processes. For most reactions illustrated in this review, reactivity and selectivity are attained through the flexible synergistic combination of different metal catalysts and additives. Further advancements will be accompanied with the discovery of innovative sulfur-directing groups, chiral catalysis, and ground-breaking experimental techniques. This article will also inspire researchers to gain a deeper understanding of the mechanism, thus undoubtedly leading to innovations and more discoveries in the future.