Gold(I)-Catalyzed Conia-ene Cyclization of Internal E-Acetylenic -Ketoesters under High Pressure.

The influence of pressure on the gold(I)-catalyzed Conia-ene cyclization of E-acetylenic--ketoesters bearing an internal alkyne moiety was investigated for the first time. The reaction catalyzed by commercially available PPh3AuNTf2 complex, which is sluggish at ambient pressure owing to steric reasons, proceeds smoothly under high-pressure conditions (6kbar). Mechanistic aspects of the reaction proceeding via 5-exo-dig and 6-endo-dig cyclization pathways were also studied employing DFT methods. Differences in the reactivity of substrates containing terminal and internal alkynes is discussed.