Bifunctional Ruthenium\nCatalysts for <i>endo</i>-Selective Cycloisomerization of\nNucleophile-Functionalized Terminal\nAlkynes

The catalytic cycloisomerization of nucleophile-functionalized\nalkynes is a useful method for the synthesis of heterocyclic compounds\nwith 100% atom economy. Group 8 catalysts give high <i>endo</i>-selectivity in these transformations due to their ability to invoke\nmetal-vinylidene intermediates. However, all known group 8 catalysts\nhave relatively low activities and require high temperatures. Here,\nwe report bifunctional ruthenium catalysts that enable the cycloisomerization\nof a large variety of substrates at low catalyst loadings and ambient\ntemperature with turnover frequencies as high as 200 s<sup>–1</sup>.