*3.3. Aryne-Enolether Substrates*

In 2017, a strategy of synthesizing indeno[1,2-*c*]quinoline derivatives was developed by the Liu group through gold(I)-catalyzed cascade cyclization with 18 examples and up to 99% yield (Scheme 19) [29]. The coordination of gold species to the *β* position of the triple bond initiated an attack of the enolether to generate indene intermediates (**86**). Intermediates (**87**) were produced by the activation of double bonds in the conjugated enolether with [Au]+, which were converted to aromatic intermediates (**88**) via intramolecular condensation with the release of MeOH after protodemetalation. In oxygen, the intermediates (**88**) were further oxidized to a more stable indeno[1,2-*c*]quinoline product (**89**). Notably, the electrondonating effect of the amine on the right benzene ring played a crucial role in the initiation of the above transformation.

**Scheme 19.** Gold(I)-catalyzed syntheses of indeno[1,2-*c*]quinoline derivatives.

In 2018, Liu et al., used 1,5-enyne substrates to synthesize a series of 2-aryl indenone derivatives in the catalysis of a gold catalyst (Scheme 20) [53]. Intermediates (**92**) were formed via a gold-catalyzed cycloisomerization. An O2-mediated radical addition to intermediates **92** afforded intermediates (**93**) that underwent aromatization to yield peroxy intermediates (**94**), which were subsequently transformed into oxonium intermediates (**95**) through the cleavage of the peroxide bond with the coordination of [Au]+. Finally, indenone products (**96**) were achieved by the hydrolysis of oxonium with the release of MeOH. The above free radical reaction process was verified via control experiments and heavy atom labeling.

**Scheme 20.** Gold(I)-catalyzed syntheses of 2-aryl indenone derivatives.
