Gold-catalyzed Hydroalkoxylation Research Articles

Thiolate Bridged Gold(I)–NHC Catalysts: New Approach for Catalyst Design and its Application to Trapping Catalytic Intermediates

New dinuclear N-heterocyclic gold complexes with bridging thiolate ligands have been designed as catalytic precursors with desired properties such as stability, recyclability and that do not require additives. The dinuclear compound [(AuNHC)2 (μ-SC6 F5 )]OTf could slowly release the active catalytic species [Au(NHC)]+ and the precursor [Au(SC6 F5 )(NHC)] in solution, which means that both species would remain stable throughout the catalytic cycle and the pre-catalyst could easily be recovered. The properties exhibited by the complexes have been taken advantage of to gain new insights on the gold-catalyzed hydroalkoxylation of alkynes, with the aim of clarifying all the steps of the catalytic cycle, together with the characterization of intermediates and final products. Isolation and characterization of the pure final spiroketals and the thermodynamic intermediate have been achieved for the first time. Moreover, the kinetic intermediate has also been detected for the first time.

Ortho-Oxygenative 1,2-Difunctionalization of Diarylalkynes under Merged Gold/Organophotoredox Relay Catalysis.

Reported herein is an ortho-oxygenative 1,2-difunctionalization of diarylalkynes under merged gold/organophotoredox catalysis to access highly functionalized 2-(2-hydroxyaryl)-2-alkoxy-1-arylethan-1-ones. Detailed mechanistic studies suggested a relay process, initiating with gold-catalyzed hydroalkoxylation of alkynes, to generate enol-ether followed by a key formal [4+2]-cycloaddition reaction. The successful application of the present methodology was also shown for the synthesis of benzofurans.

Explanation of “Silver Effects” in Gold(I)-Catalyzed Hydroalkoxylation of Alkynes

An extensive experimental NMR study of gold-catalyzed hydroalkoxylation was conducted to explain the influence of a silver salt additive on the gold-catalyzed process (silver effect). Addition of silver salt may have no effect or a negative or positive effect on gold-catalyzed hydroalkoxylation. However, silver was shown to be essentially innocent (plays no role) with regard to the mechanism of the catalytic process itself. The effect occurs only if silver induces variations in the fraction of in-cycle organogold intermediates and H+. This is associated with the formation of the argento vinyl gold species G, which was shown to be an off-cycle intermediate. This species is formed by trapping the vinyl gold species B with Ag+; in the same way, the diaurated species D (another possible off-cycle intermediate) is formed by trapping B with LAu+. The argento vinyl gold species G1 was extensively characterized in solution by various NMR techniques at different temperatures. Furthermore, bringing together our res...

Platinum- and gold-catalyzed hydroalkoxylation and tetramerization of propiolate esters

PtCl2 was found to efficiently catalyze intermolecular additions of propiolate esters with alcohols. The reaction of propiolate esters and alcohols in the presence of PtCl2 gave (E)-vinyl ethers as the major products at 60°C, whereas alkyl 3,3-dialkoxypropanoates were predominantly obtained when the reaction temperature was set to 80°C. On the other hand, a novel regioselective tetramerization of propiolate esters catalyzed by AuCl3 under mild conditions afforded 1,2,5,6-tetrasubstituted-cyclooctatetraene (1,2,5,6-COT) in moderate yields.

The Mechanism of Gold(I)‐Catalyzed Hydroalkoxylation of Alkynes: An Extensive Experimental Study

An extensive experimental study of the mechanism of gold(I)-catalyzed hydroalkoxylation of internal alkynes has been conducted by using NMR spectroscopy. This study was focused on the organogold intermediates, observations of actual catalytic intermediates in situ, and the reaction kinetics that are involved in this reaction. Based on the experimental results, a complete mechanistic picture was established, including on- and off-cycle processes that explain the role of diaurated species. We have shown that gold-catalyzed hydroalkoxylation of internal alkynes is a reaction that requires only one gold atom for the catalytic cycle, disproving a recent hypothesis regarding the involvement of cooperative gold catalysis.

An Alternative Synthesis of 2-Alkylidene-3,4-dihydro-2H-1,4-benzoxazines by Intramolecular Gold-Catalyzed Hydroalkoxylation of 2-(Prop-2-yn-1-ylamino)phenols

An efficient gold-catalyzed procedure to synthesize 2-alkylidene-3,4-dihydro-2H-1,4-benzoxazines has been developed starting from 2-alkynyl-substituted phenols. This is an intramolecular hydroalkoxylation reaction on alkynes tethered to a phenol moiety that represents a valuable alternative to the already reported transition-metal-catalyzed procedures.

Gold-Catalyzed Hydroalkoxylation of Alkoxyallenes

We report synthesis of allylic acetals via gold-catalyzed hydroalkoxylation of alkoxyallenes with alcohols containing primary and secondary alcohols in good to excellent yields under mild condition.

Gold-catalyzed intermolecular hydroalkoxylation of allenes; difference in mechanism between hydroalkoxylation and hydroamination

A wide range of alcohols 2 react with various allenes 1 in the presence of ClAuPPh 3/AgOTf catalyst at ambient temperature without solvent to produce allylic ethers 3. Contrary to the hydroamination, which proceeds through high chiral-face selectivity for chiral allenes to give the corresponding chiral allylic amines, transfer of chirality is not observed in the hydroalkoxylation, suggesting that the mechanism of the gold-catalyzed hydroalkoxylation is different from that of hydroamination.