Carboxylic Group-Assisted Proton Transfer in Gold-Mediated Thiolation of Alkynes

Combined
experimental and theoretical studies revealed a complex
mechanistic picture in which the carboxylic group-assisted proton
transfer from acetic acid to an alkyne molecule is the key step in
the unique gold-mediated alkyne transformation that leads to the formation
of gem-disubstituted vinyl gold complexes. The structures
of the complexes were unambiguously established using NMR spectroscopy
(in solution) and X-ray diffraction (in the solid state). ESI-MS study
of the reaction mixture revealed multiple gold-containing complexes
and clusters. Investigation of the MS2 fragmentation patterns
of the selected ions suggested the involvement of gold acetylides
in the transformation. Further treatment of the complexes with protic
acid led to the discovery of a novel route for the gold-mediated alkyne
hydrothiolation.