Synthesis of gem-Diaurated Species from Alkynols

A number of enol ether-derived diaurated species were synthesized directly from different alkynols and cationic gold complexes in the presence of a non-nucleophilic base (proton sponge). The reaction can be easily applied for in situ generation of diaurated species from all common types of hydroalkoxylation substrates: 5-endo, 5-exo/6-endo, 6-exo/7-endo and intermolecular types. Six examples were also synthesized in individual state as stable hexafluoroantimonate salts. Whereas diaurated species are obtained reliably from all conventional mononuclear gold catalysts, application of binuclear ones often gave diaurated species with unusual properties. The preliminary results point to complexities of behavior of binuclear gold catalysts and would require more research in future for this subclass. The formation of diaurated species from various gold-oxo compounds (LAu)2OH+, (LAu)3O+, and LAuOH (L=phosphine ligand) was also studied. Of these three types, only (LAu)2OH+ is reactive, whereas (LAu)3O+ and LAuOH are not reactive alone but require acidic promoters to enable the reaction. These differences in reactivity were explained by ability of these compounds to generate the necessary acetylene -complex intermediate.