Sustainable Access to Coumarin Derivatives: Photochemical, Electrochemical, and Biochemical Strategies Beyond Classical and Metal‐Based Methods

Coumarins are privileged scaffolds in medicinal chemistry, chemical biology, and functional materials, yet their synthesis remains dominated by classical condensations and metal‐dependent methods that limit structural diversity and sustainability. This review reframes coumarin construction through energy‐driven activation, highlighting photochemical, electrochemical, and biochemical strategies as sustainable alternatives. Visible‐light processes enable access to three‐dimensional, sp 3 ‐rich, and fused architectures that are inaccessible by conventional routes, while electrochemical methods replace stoichiometric oxidants with electrical input under metal‐free conditions. Biocatalytic and biosynthetic platforms further extend coumarin synthesis into aqueous, selective, and renewable regimes. Collectively, these paradigms align molecular innovation with modern sustainability and design principles.