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Dearomatizing spirocyclization reactions are very appealing synthetic strategies to generate functionalized three-dimensional scaffolds from simple two-dimensional precursors. Recently, the field of transition-metal-catalyzed dearomatizing spirocyclization reactions of indolyl ynones has burgeoned, as the construction of synthetically challenging quaternary spirocyclic carbons is easily achieved. In this review, we introduce an overview of advances in the transition-metal-catalyzed dearomatizing spirocyclization reactions of indolyl ynones, with the reactions being categorized according to type of catalyst.

An efficient copper-catalyzed oxidative cyclization of diynes is described. A range of functionalized γ-lactams can be readily constructed by using this protocol. This copper-catalyzed oxidative process proceeds through an alkyne oxidation, carbene/alkyne metathesis, and donor–donor carbene oxidation sequence. The use of readily available substrates, high flexibility, a simple procedure, and mild reaction conditions render the procedure a viable alternative for the preparation of functionalized γ-lactams.

Polycyclic N-heterocycles are important structural motifs commonly found in bioactive compounds, however, their selective construction via the cyclization of allenynes remains challenging yet highly desirable. Here we show a homogeneous copper-catalyzed hetero Diels−Alder (HDA) reaction of allenynes with cis-diazenes (PTAD, 4-phenyl-1,2,4-triazoline-3,5-dione), allowing the practical and efficient synthesis of a diverse array of valuable polycyclic N-heterocycles. A temperature-controlled and stereocontrolled chemoselectivity of the reaction was observed, leading to the chemodivergent synthesis of tetracyclic pyrrolidines, pentacyclic triazepanes and tricyclic pyrrolidines. Compared with related Au-catalyzed cyclization of allenynes, this copper catalysis achieves cyclization of allenynes terminating in C–N bond formation via the HDA reaction.

General access to highly valuable seven-membered rings via Büchner-type reaction remains a formidable challenge. Here we report a Cu-catalyzed intermolecular oxidation of alkynes using N-oxides as oxidants, which enables expedient preparation of valuable benzo[6,7]azepino[2,3-b]quinolines and pyridine-based diones. Importantly, in contrast to the well-established gold-catalyzed intermolecular alkyne oxidation, the dissociated pyridine or quinoline partner could be further utilized to construct N-heterocycles in this system and the reaction most likely proceeds by a Büchner-type ring expansion pathway. A mechanistic rationale for this cascade cyclization is supported by DFT calculations.