Insights into the Metal-catalyzed Alkyne Hydroarylation Reactions and Related Processes for the Synthesis of Coumarins

Coumarin derivatives play an important role in many different biomedical and technological applications. As “privileged” scaffolds, coumarin derivatives display interesting biological and important optoelectronic properties. The practical significance of coumarin molecules has encouraged extensive efforts toward their synthesis. Although classical methods, such as the Perkin, Pechmann and Knoevenagel reactions for the synthesis of a wide variety of substituted coumarins, are still actively used, these methods suffer several limitations. Nowadays, alternative new efficient syntheses of coumarin derivatives are constantly evolving and being of considerable interest. The hydroarylation reaction of alkynes, using transition metals catalysts, is considered one of the most prospective tools for rapid accessing to coumarin scaffolds in an efficient and atom-economical manner. This coumarin construction could be achieved through inter- or intramolecular reactions of respective phenols and alkynes or aryl alkynoates. The present review mainly covers recent studies on new methods for the synthesis of coumarin derivatives via alkenylation of phenols with alkynes, aryl alkynoates and related reagents or direct functionalization of alkynoates. The information provided should furnish a fresh insight for organic chemists in the design of novel molecules that contain the coumarin skeletons.