C–H Sulfidation of heterocycles: A decade update

Direct C–H sulfidation offers a step-economical approach for constructing heteroaryl sulfides by converting native C–H bonds into C–S bonds without prior substrate functionalization. This review summarizes advances reported from 2015 to 2025 in the C–H sulfidation of heterocycles, focusing on different catalytic and promoter systems rather than a single protocol. The covered methodologies include transition-metal catalysis, copper- and palladium-based systems, iodine-mediated and metal-free reactions, oxidative cross-dehydrogenative coupling, photoredox catalysis, electrochemical methods, and recyclable heterogeneous or nanocatalytic platforms. The discussion is organized according to catalyst type, sulfur source, heterocycle class, regioselectivity, and synthetic applicability. Representative substrates include indoles, imidazopyridines, pyrroles, quinolines, pyridines, thiophenes, benzothiazoles, purines, and pyrazoles. Key challenges include substrate-dependent selectivity, limited scalability, metal recovery, oxidant requirements, and sulfur-source compatibility. Future directions emphasize safer sulfur donors, earth-abundant catalysts, electrochemical or oxidant-free methods, recyclable systems, and broader site-selective protocols.