A quarter-century journey into 4-chromone derivatives: synthesis, reactions, and pioneering applications thereof

Chromone derivatives are a large family of bicyclic six-membered oxygenated heterocycles. Also, they are bioactive, naturally occurring scaffolds with unique chemical and physical features. Additionally, chromone frameworks have been utilized in various applications, ranging from drug discovery to supramolecular chemistry. This review systematically summarizes the literature on synthetic methodologies for formylchromones, cyanochromones, chromene-3-carboxylic acids, and chromene-3-malononitrile derivatives, focusing on construction strategies involving Vilsmeier-Haack and palladium-catalyzed formylation. Moreover, this report outlines advancements in chromone chemistry, highlighting recent developments, discussing substrate scope, reaction conditions, and proposed mechanistic pathways, where available. Additionally, this review covers substantial common reactions involving Diels-Alder, Prins-Nazarov, aza-Friedel-Crafts, Biginelli, Mitsunobu-triggered, and Beckmann rearrangement. Correspondingly, this review focuses on ring opening, ring expansion, heteroannulation, and the ring-closing of chromone derivatives with various heterocyclic motifs, such as pyrroles, pyridines, pyrimidines, indoles, and pyran derivatives. These collective findings underscore the potential of chromone scaffolds as promising candidates for organic synthesis and therapeutic development. Accordingly, researchers in this domain will find this overview valuable for understanding the chemistry of chromone hybrids, as it covers the literature of the last two decades.