*3.2. Arene-Enyne Substrates*

In 2016, Sanz et al., reported a gold(I)-catalyzed tandem reaction using *β,β*-diaryl-*o*- (alkynyl)styrenes to synthesize dihydroindeno[2,1-*a*]indene derivatives (Scheme 17) [51]. A 5-*endo*-cyclization was induced by the activation of [Au]+ to the alkyne, which produced carbocationic intermediates (**75**). After proton elimination and protodeauration, benzofulvene intermediates (**77**) were generated. The diene units in intermediates (**77**) were then activated by the gold species to generate allylic carbocationic intermediates (**78**), which were trapped by the neighboring electron-rich aryl group to access products (**79**). In addition, under the condition of 0 ◦C in DCM, benzofulvene intermediates (**77**) were isolated as products.

In 2022, the Sanz lab disclosed a gold-catalyzed domino method for the syntheses of indeno[2,1-*b*]thiochromene derivatives with 21 examples and 70–88% yields (Scheme 18) [52]. Activation of S/Se-substituted alkynes by [Au]<sup>+</sup> triggered the cyclization of alkene to afford cationic intermediates (**81**), the carbocations of which were trapped by the vinyl–gold to produce cyclopropyl gold carbenes (**82**). The cyclopropanes of **82** were attacked by

electron-rich aromatic groups to form ring-opening intermediates (**83**) after rearomatization. Indeno[2,1-*b*]thiochromene derivatives (**84**) containing sulfur or selenium were ultimately obtained by protodeauration. Importantly, when *(S)*-DM-SEGPHOS(AuCl)2, a chiral ligand, was used in the gold-catalyzed reaction, an enantioselective transformation was achieved in up to 80% *ee*.

**Scheme 17.** Gold(I)-catalyzed syntheses of dihydroindeno[2,1-*a*]indene derivatives.

**Scheme 18.** Gold(I)-catalyzed syntheses of indeno[2,1-*b*]thiochromene derivatives.
