*2.1. Arene-Diyne Substrates*

In 2012, Hashmi and colleagues reported a double gold(I)-activated cyclization of arene-diynes to construct benzene rings for the synthesis of *β*-substituted naphthalene derivatives, which was achieved through an unexpected reaction pathway (Scheme 1) [22]. First, one terminal alkyne of arene-diyne (**1**) was activated by a gold catalyst to form a Au– C-σ bond through catalyst transfer, and the other terminal alkyne was activated to produce a double-activated intermediate (**2**). Subsequently, the activated triple bond was attacked by the *β* carbon of gold acetylide due to π coordination, which induced the formation of a five-membered ring to generate gold–vinylidene (**3**). Next, intermediate **4** was formed by a solvent attack (benzene) and a *1,3-H* shift, which was subsequently transformed into intermediate **5** via a ring expansion. Finally, after the elimination of the gold(I) catalyst and protonation, a *β*-substituted naphthalene product (**6**) was obtained. The reaction pathway was clearly verified through X-ray crystal structure analysis of the key intermediates and controlled experiments. The strategy of double gold activation had a significant influence on the later development of gold chemistry.

**Scheme 1.** Double gold(I)-catalyzed syntheses of *β*-substituted naphthalene derivatives.

In the same year, the Ohno group described a gold(I)-catalyzed tandem approach to 1,3 disubstituted naphthalenes using arene-diynes with 14 examples, achieving a quantitative yield (Scheme 2) [23]. This strategy mainly involves intermolecular nucleophilic addition and intramolecular nucleophilic addition reactions. Gold(I)-activated terminal alkyne was first attacked by nucleophilic reagents, such as ROH, RR'NH, and Ar-H, to generate intermediates (**8**) that were immediately converted to enolether/enamine-type intermediates (**9**) by protodeauration. A subsequent 6-*endo*-dig cyclization yielded intermediates (**10**) that underwent subsequent aromatization and protonation to provide naphthalene derivatives (**11**). The above reaction path was verified in detail by the syntheses of silyl enolether intermediates (**9**) and related deuteration experiments.

**Scheme 2.** Gold(I)-catalyzed syntheses of substituted naphthalene derivatives.
