Iridium(I)-Catalyzed Intramolecular Cycloisomerization of Enynes: Scope and Mechanistic Course

We report an Ir­(I)-catalyzed cycloisomerization methodology that provides access to carbocyclic systems bearing exo-alkene moieties from alkynyl-equipped acyclic precursors. The method relies on the C–H activation of olefinic and (hetero)­aromatic C­(sp2)–H bonds, followed by an exocyclization to a tethered alkyne, and provides interesting cyclic diene products that are amenable of further elaboration. Importantly, DFT calculations suggests that, in contrast to related hydrocarbonations of alkenes in which either migratory insertions or C–C reductive eliminations have been suggested to be rate-determining, in our reactions, the energetic barrier of these steps is lower than that of the previous C–H activation.