*3.1. Arene-Diyne Substrates*

In 2012, the Hashmi group achieved the preparation of benzofulvene derivatives based on their previous strategy of double activation of diynes containing terminal alkynes (Scheme 14) [48]. Under the catalysis of a gold catalyst, dual σ/π-activated intermediates (**58**) were formed, which were rapidly transformed into gold vinylidenes (**59**) as a result of double activation. A *1,5-H* shift to electrophilic vinylidene carbon occurred, leading to intermediates (**60**). After the trapping of the carbocation by the vinyl–gold species, benzofulvene products (**61**) were synthesized in association with the elimination of the gold catalyst. The applicability of the strategy was examined by 10 examples and up to 92% yield. The above strategy was characterized by easy preparation of the substrate and a novel reaction mechanism.

**Scheme 14.** Gold(I)-catalyzed syntheses of benzofulvene derivatives.

In 2017, the Hashmi group the construction of aryl-substituted dibenzopentalene derivatives using terminally aromatic substituted 1,5-diyne substrates under gold-catalyzed conditions (Scheme 15) [49]. One of the triple bonds was coordinated by [Au]+, resulting in the attack of another electron-rich triple bond to form vinyl cation intermediates (**63**). The vinyl cation was trapped by the neighboring electron-rich benzene to produce intermediates (**64**), followed by rearomatization and protodeauration to yield intermediates (**65**). Ultimately, dibenzopentalene products (**66**) were obtained by ligand exchange of gold species. It is worth noting that benzene as a solvent was not involved in the above process to trap the vinyl cation.

In 2021, the Hashmi group developed a gold-catalyzed cycloisomerization of substituted 1,5-diynes to synthesize indeno[1,2-*c*]furan derivatives. The functional group tolerance was systematically examined using 29 examples with 16–81% yields (Scheme 16) [50]. Vinyl cationic intermediates (**68**) were formed through similar paths a those described previously in Schemes 14 and 15. Subsequently, a second annulation occurred immediately to yield oxonium intermediates (**69**). Intermediates (**71**) were produced via the release of benzyl carbocation, followed by [5,5]-sigmatropic rearrangement. Finally, indeno[1,2 *c*]furan derivatives (**73**) were obtained by rearomatization, the elimination of gold species,

and proton transfer mediated by *p*-toluenesulfonic acid (PTSA). The authors fully explained the above reaction mechanism using DFT calculations, and the high regioselectivity of [5,5]-sigmatropic rearrangement was also reasonably illustrated.

**Scheme 15.** Gold(I)-catalyzed syntheses of aryl-substituted dibenzopentalene derivatives.

**Scheme 16.** Gold(I)-catalyzed syntheses of indeno[1,2-*c*]furan derivatives.
