On the validity of Au-vinylidenes in the gold-catalyzed 1,2-migratory cycloisomerization of skipped propargylpyridines.

A mechanism of the Au-catalyzed cycloisomerization of propargylpyridines has been investigated. Both DFT computational and experimental results strongly support generation of a Au-carbene via a cyclization/proton transfer sequence over the previously proposed path involving a Au-vinylidene intermediate. For the β-Si-substituted Au-carbene (G = SiR3), a 1,2-Si migration was shown to be kinetically favored over a 1,2-H shift. This study highlights the importance of alternative pathways that could explain reactivities commonly attributed to an alkyne−vinylidene isomerization in Au catalysis.