Sulfur- and Selenium-Decorated Coumarins: Synthetic Strategies Involving Cyclization and Late-Stage Functionalization.

Chalcogen-containing coumarins have attracted considerable attention as a versatile class of heterocyclic compounds because sulfur- and selenium-substituted derivatives can significantly influence molecular reactivity, electronic characteristics, and biological activity. Over the past decades, synthetic approaches toward these compounds have advanced through two main strategies: direct construction of the coumarin framework through cyclization processes and late-stage functionalization of preformed coumarin scaffolds. This review provides a comprehensive survey of the methodologies reported over the past two decades for the preparation of chalcogen-substituted coumarins, with particular emphasis on derivatives functionalized at the C-3 and C-4 positions. Special attention is given to substrate scope, regioselectivity, mechanistic insights, and the use of modern enabling technologies as well as a literature-based quantitative analysis.