Coupling Reactions Between sp Carbon Centers

Compounds containing conjugated diynes or polyynes units continue to attract great attention of organic chemists because of the occurrence of these structural moieties in natural products. In addition, the structural motif of 1,3-diyne has been recognized to play an important functionality in the properties of many functional materials (e.g., macrocyclic annulenes, organic conductors, supramolecular switches, and carbon-rich materials). Thus, over the last decade, the synthesis of conjugated diynes has been a topic of current interest and significant efforts have been directed toward the development of new and efficient methods for their synthesis, especially unsymmetrical diynes. This chapter presents an overview of the most relevant development in this field, with a focus on catalytic systems mediated by copper or by a combination of palladium and copper salts for the efficient homo- and heterocoupling of acetylenic substrates. Reactions involving new protocols such as decarboxylative couplings are also reported, along with miscellaneous transformations.