2,3-Dichloro-5,6-Dicyano-1,4-Benzoquinone (DDQ)-Mediated CC Bond Formation: Redox Strategies from Stoichiometric to...

2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) has long been recognized as a versatile organic oxidant that mediates diverse transformations through single-electron transfer, hydride abstraction, and redox cycling. Beyond its classical stoichiometric role in oxidation and dehydrogenation, DDQ now serves as an efficient catalyst for carbon-carbon bond formation across thermal, photochemical, and electrochemical domains. In stoichiometric reactions, DDQ enables benzylic and allylic CH activation to generate oxocarbenium or iminium intermediates that couple with a broad range of nucleophiles, facilitating alkylation, arylation, cyanation, and annulation processes. In catalytic systems, DDQ participates in redox cycles where the DDQ/DDQH₂ couple is regenerated by oxidants such as O₂, nitrites, or MnO₂, offering mild and simple access to complex carbon frameworks. The scope further extends to asymmetric catalysis and radical-mediated cross-dehydrogenative coupling, providing sustainable routes to natural product-like scaffolds and biologically active molecules. This review highlights the progression of DDQ from a stoichiometric oxidant to a redox-active catalyst, emphasizing its growing utility in controlled, metal-free oxidative CC bond formation and its promise for next-generation sustainable synthesis.