Access to Functionalized Isocoumarin Via Palladium-Catalyzed Tandem Heck Cyclization/Lactonization

A palladium-catalyzed tandem Heck cyclization/lactonization reaction has been developed for the efficient construction of functionalized isocoumarins. This tandem reaction forms two carbon-oxygen bonds and two carbon-carbon bonds in a single operation. The mechanism of this reaction involves sequential intramolecular Heck cyclization, alkyne coordination, and nucleophilic attack by oxygen. Mechanistic studies indicate that water or the base serves as oxygen source and that the aryl iodide substrate plays a dual role as both a coupling partner and an oxidant.