State-of-the-art transition metal-catalyzed approaches to quinoline frameworks via multicomponent reactions

Quinoline derivatives are vital nitrogen-containing heterocycles that are widely utilized in pharmaceuticals, agrochemicals, and materials science. Recent advancements have highlighted the effectiveness of multi-component reactions (MCRs) as efficient and versatile strategies for constructing these complex molecules, offering high atom economy, operational simplicity, and broad structural diversity. Transition metal catalysts such as palladium, copper, iron, and silver have been instrumental in optimizing quinoline synthesis via MCRs, significantly enhancing the reaction efficiency, selectivity, and scope. These catalysts facilitate key transformations, including cyclization, C-C and C-N bond formation, and oxidative coupling under mild conditions. This review offers a comprehensive overview of the state-of-the-art transition metal-catalyzed MCR approaches for quinoline construction, emphasizing the reaction mechanisms, catalytic performance, and developments in sustainable methodologies. Additionally, it discusses future directions for catalyst design and expands on the synthetic potential of these methodologies to meet emerging scientific and industrial needs.