Bifunctional Ruthenium Catalysts for <i>endo</i>-Selective Cycloisomerization of Nucleophile-Functionalized Terminal Alkynes

The catalytic cycloisomerization of nucleophile-functionalized alkynes is a useful method for the synthesis of heterocyclic compounds with 100% atom economy. Group 8 catalysts give high endo-selectivity in these transformations due to their ability to invoke metal-vinylidene intermediates. However, all known group 8 catalysts have relatively low activities and require high temperatures. Here, we report bifunctional ruthenium catalysts that enable the cycloisomerization of a large variety of substrates at low catalyst loadings and ambient temperature with turnover frequencies as high as 200 s–1.