Simple Silver Salts and Palladium Bis(N-heterocyclic carbene) Complexes As Complementary Catalysts for the Nazarov Cyclization

Simple silver salts and dicationic palladium bis(N-heterocyclic carbene) complexes were found to be effective and complementary catalysts for Nazarov cyclizations of divinyl β-keto esters. A sterically hindered palladium bis(NHC) catalyst provided remarkable endo:exo selectivity in cyclizations of cyclohexenyl β-keto esters, whereas AgSbF₆ gave improved yields with electron-deficient substrates. The high activities observed with silver salts are significant, given their widespread use as additives in catalytic Nazarov reactions.