Recent advances in the total synthesis of coumarin-based natural products

Coumarins represent an important class of oxygenated heterocyclic natural products widely distributed in plants, fungi, and microorganisms. Their remarkable structural diversity ranges from simple oxygenated coumarins to complex fused architectures such as pyranocoumarins, benzocoumarins, coumestans, lamellarins, and other annulated frameworks. Because many naturally occurring coumarins are available only in limited quantities from natural sources, chemical synthesis plays a crucial role in structural confirmation, biological evaluation, and the development of functional analogues. Over the past decades, significant advances have been achieved in the synthesis of coumarin-based natural products through the development of modern synthetic methodologies. These include transition-metal-catalyzed cross-coupling reactions, C-H activation strategies, oxidative annulations, multicomponent reactions, biomimetic transformations, and cascade processes that enable the rapid construction of structurally complex coumarin frameworks. This review highlights and critically examines progress in the synthesis of naturally occurring coumarins, focusing on representative total syntheses and key transformations used to assemble diverse coumarin architectures. Particular emphasis is placed on reaction design, synthetic strategy, and methodological innovations that enable efficient access to biologically significant coumarin natural products and their derivatives.