**3. Gold(III) asymmetric transformations**

Opposite to gold(I), gold(III) complexes have a square-planar geometry that allows ancillary ligands to be closer to the substrate, what made them good candidates for the development of asymmetric transformations. However, its enormous tendency to be reduced, have hampered it use in catalysis. Some recent studies have found the way to stabilize gold(III) centers, while maintaining its catalytic activity, placing them into cyclometalated frameworks. NHC-biphenyl gold(III) complexes with a cyclometalated structure, showed enough stability to catalyze an enantioconvergent kinetic resolution of 1,5-enynes (**Figure 17**, Ec. 1) [56]. In this reaction racemic 1,5-enynes are converted to bicyclo[3.1.0]hexenes with enantiomeric ratios up to 88%. Each enantiomer of the starting 1,5-enyne led to the same bicyclo with different enantioselectivity, making the overall enantioselectivity decrease with the conversion. Because of the latter, the conversions were maintained below, 50%. A related NHC-biphenylene gold(III) catalyst has been applied to enantioselective γ,δ-Diels-Alder reactions. In this occasion enantioselectivities reached 97% and yields were up to 87%. Detailed mechanistic studies revealed that the enantio- discrimination come from non-covalent π-π interactions between the substrate and an aromatic group of the complex (**Figure 17**, Ec. 2) [57].

Other cyclometalated complexes, such as cyclometalated oxazoline gold(III) complexes incorporating a biphenol ligand, have shown to be able to catalyze the asymmetric carboalkoxylation of alkynes. The corresponding 3-alcoxyindanones are obtained with moderate to good enantioselectivities. Remarkably, in this reaction camphorsulonic acid (CSA) activate the gold complex avoiding the need of adding silver salts as activators. Mechanistic studies suggested that the active catalytic specie is formed through protodeauration of one of the oxygens of the biphenol ligand (**Figure 18**) [58].

**Figure 17.** *Asymmetric transformations with chiral NHC-biphenyl gold(III) complexes.*

**Figure 18.**

*Asymmetric carboalkoxylation of alkynes with gold(III) complexes.*
