22609-96-7Relevant academic research and scientific papers
Influence of a very bulky N- Heterocyclic Carbene in Gold-Mediated Catalysis
Gomez-Suarez, Adrian,Ramon, Ruben S.,Songis, Olivier,Slawin, Alexandra M. Z.,Cazin, Catherine S. J.,Nolan, Steven P.
scheme or table, p. 5463 - 5470 (2011/12/13)
The syntheses of the free carbene IPr* (IPr* = 1,3-bis(2,6-bis(diphenylmethyl)-4-methylphenyl)imidazol-2-ylidene) and related gold complexes [Au(IPr*)Cl] (C1) and [Au(IPr*)(NTf2)] (C2) were achieved in high yields. The % VBur of IPr* for both gold complexes was measured, revealing IPr* as one of the bulkiest NHCs on gold complexes reported to date. In addition, the catalytic activity of C1 and C2 in several reactions, typically catalyzed by AuI complexes, was investigated. Examples include the tandem alkoxylation/lactonization of γ-hydroxy-α,β-acetylenic esters, the [3,3]-rearrangement of propargylic acetates leading to the formation of conjugated enones and substituted indenes, and the rearrangement of allylic acetates. These studies revealed a strong solvent effect on the catalytic activity with 1,2-dichloroethane as the solvent of choice. The screening of C1 and C2 demonstrated only slightly diminished activities in comparison to [Au(NHC)(L)] complexes bearing bulky ligands such as IPr and SIPr.
Gold(I)-catalyzed tandem alkoxylation/lactonization of γ-hydroxy- α,β-acetylenic esters
Ramon, Ruben S.,Pottier, Christophe,Gomez-Suarez, Adrian,Nolan, Steven P.
, p. 1575 - 1583 (2011/08/04)
The formation of 4-alkoxy-2(5H)-furanones was achieved via tandem alkoxylation/lactonization of γ-hydroxy-α,β-acetylenic esters catalyzed by 2 mol% of [2,6-bis(diisopropylphenyl)imidazol-2-ylidine]gold bis(trifluoromethanesulfonyl)imidate [Au(IPr)(NTf2)]. The economic and simple procedure was applied to a series of various secondary propargylic alcohols allowing for yields of desired product of up to 95%. In addition, tertiary propargylic alcohols bearing mostly cyclic substituents were converted into the corresponding spiro derivatives. Both primary and secondary alcohols reacted with propargylic alcohols at moderate temperatures (65-80 °C) in either neat reactions or using 1,2-dichloroethane as a reaction medium allowing for yields of 23-95%. In contrast to [Au(IPr)(NTf2)], reactions with cationic complexes such as [2,6-bis(diisopropylphenyl)imidazol-2-ylidine] (acetonitrile)gold tetrafluoroborate [Au(IPr)(CH3CN)][BF4] or (μ-hydroxy)bis{[2,6-bis(diisopropylphenyl)imidazol-2-ylidine]gold} tetrafluoroborate or bis(trifluoromethanesulfonyl)imidate - [{Au(IPr)} 2(μ-OH)][X] (X=BF4, NTf2) - mostly stop after the alkoxylation. Analysis of the intermediate proved the exclusive formation of the E-isomer which allows for the subsequent lactonization. Copyright
[(NHC)AuCl]-catalyzed Meyer-Schuster rearrangement: scope and limitations
Ramón, Rubén S.,Marion, Nicolas,Nolan, Steven P.
experimental part, p. 1767 - 1773 (2009/06/18)
An efficient catalytic system allowing for the synthesis of a variety of α,β-unsaturated ketones has been developed. [(NHC)AuCl] (NHC{double bond, long}N-heterocyclic carbene) in the presence of a silver(I) salt was found to catalyze the Meyer-Schuster rearrangement, leading to α,β-unsaturated ketones from easily accessible propargylic alcohols in high yields. Catalysis was performed in a 2:1 mixture of methanol and water at 60 °C and afforded good yields even for tertiary alcohols and sterically demanding substrates. Thorough evaluation of the present catalytic system uncovered that it was unsuitable for terminal alkynes and primary alcohols. In these cases low yields of the target molecules were obtained due to the formation of unexpected by-products.
β- and α-LITHIATION OF METHYL β-METHOXYACRYLATE: EFFICIENT SYNTHESIS OF α,γ-SUBSTITUTED METHYL TETRONATES - STRUCTURE OF ASPERTETRONINS AND GREGATINS
Miyata, Okiko,Schmidt, Richard R.
, p. 1793 - 1796 (2007/10/02)
Methyl β-methoxyacrylate (1) can be lithiated succesively in β- and α-positions.Reaction with two electrophiles (at first a carbonyl compound) leads to α,γ-substituted methyl tetronates in a two step synthesis.Application of this method to the synthesis of methyl tetronate whose structure was assigned as that of gregatin B indicates that the gregatins and aspertetronins have the isomeric structures 17.
