Stereoselective Gold(I)-Catalyzed Intermolecular Hydroalkoxlation of Alkynes

Abstract

We report the use of cationic gold complexes [Au(NHC)(CH3CN)][BF4] and [{Au(NHC)}2(μ–OH)][BF4] (NHC = N-heterocyclic carbene) as highly active catalysts in the solvent-free hydroalkoxylation of internal alkynes using primary and secondary alcohols. Using this simple protocol, a broad range of (Z)-vinyl ethers were obtained in excellent yields and high stereoselectivities. The methodology allows for the use of catalyst loadings as low as 200 ppm for the addition of primary alcohols to internal alkynes (TON = 35 000, TOF = 2188 h–1).

Hydroalkoxylation of Terminal and Internal Alkynes Catalyzed by Dinuclear Gold(I) Complexes with Bridging Di(N-Heterocyclic Carbene) Ligands

“…Ligand L is instead a spectator ligand that stabilizes the active form of the catalyst and modulates its steroelectronic properties. Among the different available L-type ligand classes, those achieving the best performances are phosphines and N-heterocyclic carbenes (NHCs) [4][5][6].…”

A Triflamide‐Tethered N‐Heterocyclic Carbene–Rhodium(I) Catalyst for Hydroalkoxylation Reactions: Ligand‐Promoted Nucleophilic Activation of Alcohols

“…[4] Whereasmetal-catalyzed intramolecular hydroalkox-ylationsa re well reported, [5] intermolecular reactions between alcohols and alkynes are difficult [6] and often demandt he use of as trong base or harsh conditions. [14] Herein, we report the design, synthesis, and catalytic activity of aR h I -NHC dicarbonylc omplexf eaturing at etheredt riflamide group for the intermolecular addition of alcohols to terminal alkynes and the intramolecular cycloisomerization of alkynols (Scheme 2). [8] A [PdMo 3 S 4 (1,4,7-triazacyclononane) 3 Cl] 3 + cubane cluster with CF 3 SO 3 Ag was reported to catalyze the anti-Markovnikov hydroalkoxylation of alkynica cid esters.…”

“…[7] Kirchner reported the addition of allylic alcohols to phenylacetylene by using the [RuCl{tris(pyrazolyl)borate}(pyridine) 2 ]c atalyst. [14] Herein, we report the design, synthesis, and catalytic activity of aR h I -NHC dicarbonylc omplexf eaturing at etheredt riflamide group for the intermolecular addition of alcohols to terminal alkynes and the intramolecular cycloisomerization of alkynols (Scheme 2). [9] Kakiuchif irst reported the intermolecular anti-Markovnikov hydroalkoxylation of terminal acetylenes by using an 8-quinolinolato-ligated rhodium(I) dicarbonyl complex.…”

“…[11] Computational studies by Wang and co-workersr evealed that the 8-quinolinolato oxygen atom facilitated alcohold eprotonation to am ore potent On ucleophile, which readily added to the Rh-vinylidene followed by protont ransfers. [14] Herein, we report the design, synthesis, and catalytic activity of aR h I -NHC dicarbonylc omplexf eaturing at etheredt riflamide group for the intermolecular addition of alcohols to terminal alkynes and the intramolecular cycloisomerization of alkynols (Scheme 2). [13] We postulated that aN HC with ap endant basic group would be ideallys uited for alcohol activation and promotei ts nucleophilic attack to the metal-vinylidene.…”

The preference for dual-gold(i) catalysis in the hydro(alkoxylation vs. phenoxylation) of alkynes

“…13,14 Well-defined digold pre-catalysts are now used for a number of applications. [15][16][17][18][19][20][21][22][23] Dual gold catalysis might help to overcome the hurdle that Au I has only two coordination sites available, with a linear geometry. 24 Another issue that remains is that understanding how ligand structure affects reactivity in catalysis, although some useful empirical observations have been made.…”