An Improved Gold(I) Catalytic System for the Preparation of Coumarins via Intramolecular Cyclization

A catalytic system comprising a gold(I) complex with an N- heterocyclic carbene (NHC) ligand in an ionic liquid as solvent exhibits higher catalytic efficiency compared to state of the art systems in the title reaction, which enables using down to 0.01 mol % gold. A commercial gold(I) catalyst such as IPrAuNTf2 can be employed for this purpose. In the case of less reactive substrates bearing electron-withdrawing substituents at the phenol moiety, a tailor made NHC-gold(I) precatalyst exhibits improved reactivity and can be advantageously employed compared to the commercial one.