The document discusses the development of metal-catalyzed carbon-carbon and carbon-heteroatom cross-coupling reactions as important synthetic methods. Specifically, it mentions the development of copper-based catalysts for cross-coupling reactions as an alternative to traditional palladium-based systems. Copper-assisted Sonogashira coupling reactions, which form carbon-carbon bonds between aryl halides and terminal alkynes, are highlighted as valuable transformations for producing substituted internal alkynes that are useful building blocks in many applications.