Reactions of Cationic Gold(I) with Allenoates: Synthesis of Stable Organogold(I) Complexes and Mechanistic Investigations on Gold-Catalyzed Cyclizations

The reaction of allenoates with cationic gold (I)-generated in situ from a phosphine gold chloride and a silver salt-formed unusual, room temperature stable vinyl gold(I) lactones under very mild conditions. The scope and limitations for the synthesis of this novel organogold complex was investigated. DFT calculations oil the highest occupied molecular orbitals (HOMOs) of allenoates and the natural bond orbital (NBO) charge densities provided an explanation for the limitations. A plausible mechanism for its formation was proposed based on in situ H-1 and P-31 NMR spectroscopic analyses. Controlled experiments for the cleavage of the gold-carbon bond by electrophiles indicated that this vinyl gold(I) complex is the likely intermediate in the gold-catalyzed reaction of carboncarbon multiple bonds.