4-Chloro-3-formylcoumarin as a multifaceted building block for the development of various bio-active substituted and fused coumarin heterocycles: a brief review

This paper reviews the research data available in the literature on the chemistry of 4-chloro-3-formylcoumarins reported over the last two to three decades. It covers the synthetic applicability of 4-chloro-3-formylcoumarins in the development of 3,4-substituted coumarins as well as 5-, 6- and 7-membered ring fused coumarin derivatives via classical reaction protocols, microwave-mediated reactions, organo-catalyzed reactions, transition metal-catalyzed reactions, and green reaction protocols. This review presents the diverse synthesis of 3,4-substituted coumarins and 5-, 6- and 7-membered ring fused coumarins using 4-chloro-3-formylcoumarin as the precursor via classical reactions including metal-catalyzed and green reaction protocols.