Uemura, here you go:
Esters are effective co-catalysts in copper-catalyzed methanolysis of aryl bromidesPatrice Capdevielle, and Michel MaumyTetrahedron Letters 34(6), 1007-1010 (1993)
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https://www.thevespiary.org/rhodium/Rhodium/pdf/arylhalide.methanolysis.cu-etoac.pdf)
AbstractAnisole is also quasi-quantitatively obtained from bromobenzene in presence of ethylacetate (10 mmole C6H5Br, 4 mmol EtOAc, 1.4 mmol CuBr in 6 ml 5M MeONa/MeOH, 98% conversion after lh reflux, 100% after 2h, yield of isolated anisole > 95% without detected phenetole).
Copper-catalyzed reaction of sodium methoxide with aryl bromides in methanol is generally a method of value for the preparation of methyl aryl ethers(1) : However, this process is often sluggish or even ineffective in the case of unactivated (devoid of electron withdrawing substituents Z) aryl bromides such as bromobenzene, and various studies have been undertaken to resolve this problem. Several publications and patents claimed that amide co-solvents such as N,N-dimethylformamide (DMF) were very useful,(2a-d) allowing satisfacting solubility and stability of cuprous salts catalysts, which are less soluble and readily disproportionate in methanol alone. Remaining disadvantage was the high cost of such solvents face to methanol, and R. J. Bryant reported that formamides could be replaced by alkyl formates,(3) in relatively small proportions toward methanol solvent. Methoxylation of bromobenzene so proceeds in 56% yield and 2-bromophenol is quantitatively converted into guaiacol.
More recently, H. L. Aalten et al. revisited this chemistry, concluding inter alia that amide co-solvents (DMF) were quite effective to obtain a quantitative bromobenzene + anisole substitution, but methyl formate was curiously found to have no effect on reaction rate in methanol.(4)
Another example, of industrial interest, is the transformation of 5-bromovanilline into syringaldehyde : substrate (5 mmol) is refluxed with EtOAc (3 mmol) and CuBr (1 mmol) in 5 M MeONa / MeOH (10 ml) for 14 h; classical work-up leads to pure syringaldehyde (95%). When starting from more soluble 5-bromovanilline dimethyl acetal, reaction is achieved within two hours (yield 98%).
Hence, the positive influence of esters on the course of these aromatic copper-catalyzed substitutions is well established. and the necessity of high methoxide concentration is checked and explained by the following findings:
Whereas copper(I) bromide (or chloride) catalyst, once added to methoxide solution, gives rise to unsoluble yellow copper(I) methoxide, which decomposes under refluxing to C
0 and C
2, presence of an ester in concentrated (3 to 5 M) methoxide solutions prevents precipitation of copper(I) methoxide, but provides a colorless mixture in which added aryl bromides are readily transformed into methyl aryl ethers. Use of smaller amounts of copper (0.5 mmol CuBr in 15 ml 4M MeONa / MeOH) even leads to colorless clear solutions (copper complex and NaBr are entirely soluble under MeOH refluxing). Lower methoxide concentrations (up to 2.5 M) render esters co-catalysts uneffective, as copper(I)methoxide remains unsoluble; further addition of methoxide to the mixture leads again to clear solutions.
High efficiency of ethyl acetate is not due to any baso-catalyzed condensation into ethyl acetoacetate, since the latter has a negative effect on the reaction: it slows the rate down to c.a. 75% of the blank’s one when added to the 2-bromophenol / CuBr/MeONa system. The observed stabilization and increased solubility of Cu(1) catalyst in presence of esters MeO-CO-R - even unenolixable - can then be attributed to their adduct with methoxide ion, obtained at high concentrations of the latter, and written as follow:
(proposed mechanism here)
Tetrahedral intermediate 1 is well known to be formed in very small amounts during baso-catalyzed methanolysis of esters;(5a,b) it is obviously here a potent ligand for added copper(I), tentatively drawn as complex 2, allowing in turn the substitution ArBr + ArOMe to proceed with a great etBciency. Such a stabilization of primary catalyst, and also probably of various Cu(II) or Cu(III) intermediate species previously proposed to occur in the aromatic substitutioneitself, implies ester to be substantially transformed (CuOMe no more precipitates from 5M MeONa solution).
This work was partly performed with financial support from Rhane-Poulenc Chimie, and industrial applications are patented.(9)
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Patent DE2627874
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Patent US4218567
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Patent GB2089672
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Post 477850
(Rhodium: "ArBr --NaOMe/Cu(I)--> ArOMe", Chemistry Discourse)(5a)Bender, M. L. Chem. Rev. 1960,60,53 - 113.
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(9)Capdevielle, P.; Maumy, M.; Nobel, D. (Rhane-Poulenc Chimie):
Patent FR2669922
1992.