Mechanism of Au(III)-Mediated Alkoxycyclization of a 1,6-Enyne

Gold-mediated homogeneous catalysis is a powerful tool for construction of valuable molecules and has lately received growing attention. Whereas Au­(I)-catalyzed processes have become well established, those mediated by Au­(III) have so far barely been explored, and their mechanistic understanding remains basic. Herein, we disclose the combined NMR spectroscopic, single-crystal X-ray crystallographic, and computational (DFT) investigation of the Au­(III)-mediated alkoxycyclization of a 1,6-enyne in the presence of a bidentate pyridine-oxazoline ligand. The roles of the counterion, the solvent, and the type of Au­(III) complex have been assessed. Au­(III) is demonstrated to be the active catalyst in alkoxycyclization. Alkyne coordination to Au­(III) involves decoordination of the pyridine nitrogen and is the rate-limiting step.