Mechanistic Study of Gold(I)-Catalyzed Hydroamination of Alkynes: Outer or Inner Sphere Mechanism?

An experimental mechanistic study of the gold(I)catalyzed hydroamination shows the formation of conformationally flexible auro-iminium salts Au-Im, which originate from the protonation of a vinyl gold species. Rotation around the C-CAu bond is the reason for the loss of stereospecificity of protodeauration, which explains the stereochemical result of the Stradiotto reaction. The ambiguity about inner or outer sphere mechanism is thus resolved in favor of the outer sphere mechanism.