Recent Developments in Transition-Metal-Catalyzed Tandem C─H Activation/Cyclization of α,ω-Diynes

Transition-metal-catalyzed C-H activation has emerged as a powerful tool for constructing diverse heterocycles and efficiently increasing molecular complexity in a single operation. Compared with the well-studied diyne [2 + 2 + 2] cycloaddition, diyne-involved C-H functionalization represents a promising evolution of this field. The inherent reactivity of diynes enables sequential participation of both alkyne units in relay processes, a feature central to their utility. Recent years have witnessed remarkable progress in diyne-based C-H functionalization/cyclization with exquisite site- and chemoselectivity, spanning substrate control strategies, catalysis design, reaction development, mechanistic insights, substrate scope, and practical applications. Organized by the type of diyne and reaction patterns, this review highlights recent advances in transition-metal-catalyzed tandem C-H functionalization/cyclization reactions of 1,6-diynes, 1,5-diynes, 1,4-diynes, and other tethered diyne substrates, with a focus on the assembly of 1,3-dienes, polycyclic aromatic hydrocarbons, π-conjugated polymers, polyheterocycles, and related structures. Notably, this review focuses exclusively on reactions where both alkyne units participate in tandem processes, excluding cases where only one alkyne acts as a π-coupling reagent.