Silver‐Catalyzed [5+2] Cycloaddition of Terminal Alkynes With Imidazolidines: Access to 1,4‐Diazepines

Herein, we report a silver‐catalyzed [5+2] cycloaddition of terminal alkynes with imidazolidines, enabling the efficient synthesis of 1,4‐diazepines under mild conditions. The imidazolidine substrate acts as a novel 5‐atom synthon, undergoing silver‐mediated cyclization with terminal alkynes to deliver diverse 1,4‐diazepines in up to 92% yield with excellent functional group tolerance. This method provides a convenient route to access the privileged seven‐membered diazacyclic core, which is widely found in pharmaceuticals and bioactive molecules. Notably, the catalytic system is also applicable to the formal [6+2] cycloaddition of terminal alkynes with hexahydropyrimidines, allowing the construction of synthetically challenging eight‐membered diazacycles.