Modular approaches, which allow a systematic variation of heteroaromatic cores and substituents, are crucial for the development of heteroaromatic drug candidates and organic functional materials. A new strategy involving the cyclization of heteroarenes tethered with alkynes through a norbornene bridge was developed. The precursors were readily prepared by a three‐component coupling process of heteroaryl halides, norbornadiene, and terminal alkynes. The Pd catalytic system derived from Pd(OAc)2 and 2‐(pyrazol‐1‐yl)pyridine transformed a variety of five‐membered heteroarenes to the corresponding benzofused products, including (di)benzothiophene, indazole, carbazole, indole, and benzofuran, with aryl and alkyl substituents at the C4(C7) position. During the cyclization process, the norbornene ring underwent a retro‐Diels‐Alder reaction, serving as an acetylene synthon. This approach was used to synthesize naphthalene derivatives from electron‐rich arenes, demonstrating its versatility in the annulation of (hetero)aromatic rings.

In this study, Au(III)-catalyzed cyclization reactions of alkynyl norbornene derivatives were developed to provide benzofused (hetero)arenes with substitutions at the benzocyclic ring. The combination of Au(OAc)3 and AgNTf2 allowed for the annulation of (hetero)arenes by intramolecular hydro(hetero)arylation followed by retro-Diels–Alder reactions to afford fully conjugated benzofused (hetero)arenes in higher yields as compared to the yield obtained using our previously developed Pd(OAc)2-catalyzed protocol. Furthermore, when Au(OAc)3 was replaced with AuCl3, (hetero)arenes with the norbornene bridge installed at the more electron-rich and sterically demanding position underwent a rearrangement to afford the corresponding regioisomeric products in a divergent manner. The result indicates that the rigid norbornene ring creates a steric effect, in addition to placing two reactive sites in proximity and serving as an acetylene synthon. This illustrates the importance of the steric effect in addition to the electronic effects of the catalyst and substrate on the rearrangement.