Gold‐Catalyzed Annulations with Nucleophilic Nitrenoids Enabled by Heteroatom‐Substituted Alkynes.

The combination of a nucleophilic nitrene equivalent, a triple bond and a π‐acid catalyst has underpinned numerous efficient transformations for the preparation of azacycles. This personal account details our efforts in developing an annulation strategy. Adding a nucleophilic nitrenoid to an activated alkyne can generate carbenoid character that is then quenched by a cyclisation onto the nitrenoid substituent. The use and development of N‐acyl and N‐heterocyclic pyridinium‐N‐aminides as 1,3‐N,O and 1,3‐N,N‐dipole equivalents is discussed in the context of oxazole and heterocycle‐fused imidazole formation, respectively. The resulting processes are highly efficient, practically straightforward, and tolerate considerable structural and functional group variation. Our use of heteroatom‐substituted alkynes as enabling tools for reaction discovery is discussed. The reactivity accessed from the strong donor‐like properties of ynamides is complemented by that obtained from alkynyl thioethers, which are emerging as interesting substrates for π‐acid catalysis. [ABSTRACT FROM AUTHOR]