Overriding the alkynophilicity of gold: catalytic pathways from higher energy Au(I)-substrate complexes and reactant deactivation via unproductive complexation in the gold(I)-catalyzed propargyl Claisen rearrangement.

Computational and experimental analysis of unusual substituent effects in the Au-catalyzed propargyl Claisen rearrangement revealed new features important for the future development of Au(I) catalysis. Despite the higher stability of Au-alkyne complexes, they do not always correspond to the catalytically active compounds. Instead, the product emanates from the higher energy Au(I)-oxygen complex reacting via a low barrier cation-accelerated oxonia Claisen pathway. Additionally, both intra and intermolecular competition from other Lewis bases present in the system, for the Au(I) catalyst, can lead to unproductive stabilization of the substrate/catalyst complex, explaining hitherto unresolved substituent effects.