"Silver effect" in gold(I) catalysis: an overlooked important factor.

Clear experimental evidence from X-ray photoelectron spectroscopy and (31)P NMR spectroscopy has been obtained for the first time to confirm that the combination of Ag(+) cation with [L-Au](+) results in the formation of different complexes in solution. Re-evaluation of literature-reported gold-catalyzed reactions revealed a significant difference in the reactivities with and without silver. In extreme cases (more than "rare"), the conventional [L-Au](+) catalysts could not promote the reaction without the presence of silver. This investigation has therefore revealed a long-overlooked "silver effect" in gold catalysis and should lead to revision of the actual mechanism.

Ligand-controlled gold-catalyzed cycloisomerization of 1,n-enyne esters toward synthesis of dihydronaphthalene.

We describe herein a gold-catalyzed rearrangement of propargyl esters followed by allene-ene cyclization to afford substituted bicyclic [4.4.0] dihydronaphthalene compounds. This method is also applied to vinylethers and vinylamines of 1,7-enyne esters to form dihydroquinoline and dihydrobenzopyran structures. The basis of this transformation is the ligand-controlled preferential activation of the alkene over the allene, affording the desired aromatic bicyclic structures in moderate to excellent yields.