A new strategy for gold and palladium dual-catalytic reactivity and turnover, called catalyzed catalysis, enhanced the synthetic usefulness of vinylgold intermediates by providing dual-catalytic carbon-carbon cross-coupling as an alternative to protodemetalation. This protocol enabled the synthesis of substituted butenolides and isocoumarins from allyl esters. Kinetic and spectroscopic experiments support a mechanism in which the Lewis acidic gold complex catalyzes both an initial rearrangement step and a subsequent Lewis basic palladium oxidative-addition step.

The relative kinetic basicities of a series of differentially substituted and hybridized neutral organogold compounds were examined through competitive protodeauration experiments and were found to span 2.2 orders of magnitude. The effect of electron-withdrawing and electron-donating substituents on the rate of protodeauration of alkenylgold and arylgold compounds was explored. An acid counterion effect indicated the presence of a gold-mediated substrate preequilibrium before protodemetalation, and hybridization effects and a Hammett correlation with F þ = -0.41 indicated the involvement of the C-C π system in the protodeauration of vinylgold, alkynylgold, and arylgold complexes.

A vinyl aziridine activation strategy cocatalyzed by palladium(0) and a gold(I) Lewis acid has been developed. This rearrangement installs a C–C and a C–N bond in one synthetic step to form pyrrolizidine and indolizidine products. Two proposed mechanistic roles for the gold cocatalyst were considered: (1) carbophilic gold catalysis or (2) azaphilic gold catalysis. Mechanistic studies support an azaphilic Lewis acid activation of the aziridine over a carbophilic Lewis acid activation of the alkene.

Double-label crossover, modified-substrate, and catalyst comparison experiments in the gold and palladium dual-catalytic rearrangement/cross-coupling of allenoates were performed in order to probe the mechanism of this reaction. The results are consistent with a cooperative catalysis mechanism whereby 1) gold activates the substrate prior to oxidative addition by palladium, 2) gold acts as a carbophilic rather than oxophilic Lewis acid, 3) competing olefin isomerization is avoided, 4) gold participates beyond the first turnover and therefore does not serve simply to generate the active palladium catalyst, and 5) single-electron transfer is not involved. These experiments further demonstrate that the cooperativity of both gold and palladium in the reaction is essential because significantly lower to zero conversion is achieved with either metal alone in comparison studies that examined multiple potential gold, palladium, and silver catalysts and precatalysts. Notably, employment of the optimized cocatalysts, PPh3AuOTf and Pd2dba3, separately (i.e., only Au or only Pd) results in zero conversion to product at all monitored time points compared to quantitative conversion to product when both are present in cocatalytic reactions.

A new Heck-type reaction accessed the migratory insertion chemistry of palladium from organogold complexes. Observation, isolation, and characterization of a palladium intermediate established the role of gold/palladium transmetalation in this reaction. Recent reports of combining the reactivity of organogold compounds with palladium in organic synthesis generally assume a gold-to-palladium transmetalation step, although this step had not been directly observed in these reactions. The results herein furnish experimental evidence for the mechanisms of reactions mediated or catalyzed by both gold and palladium and reveal a migratory insertion strategy for outcompeting homocoupling pathways.