Direct Coumarin Synthesis by Gold Catalyzed Hydroarylation of Alkynoic Acids/Esters

The combination of a gold(I) catalyst with a small amount of ionic liquid as solvent creates a catalytic system able to efficiently promote the direct synthesis of coumarins from phenols and alkynoic acids/esters, through a reaction sequence involving gold-catalyzed intermolecular direct alkyne hydroarylation followed by intramolecular thermal/acid catalyzed (trans)esterification. The reaction is highly atom economical and works well under mild conditions, relatively short reaction times and < 1% Au, particularly in the case of phenols substituted with electron-donating groups and propiolic acid as substrates. Furthermore, the gold/IL catalytic system proved recoverable and recyclable.