Copper benzimidazole

Benzimidazole was iodinated at the 2-position to form a copper-benzimidazole complex 246 by treatment with Cul and KI in aqueous ammonium hydroxide (Scheme 59) <2005CE0514>. 

Table 3 Stereochemistries of copper(II) complexes of benzimidazole-based chelating ligands.

Whereas pyrrole was reported not to give N/H insertion by ketocarbenoids, such a reaction mode does occur with imidazole Copper-catalyzed decomposition of ethyl diazoacetate at 80 °C in the presence of imidazole gives ethyl imidazol- 1-ylacetate exclusively (93 %) small amounts of a C-alkylated imidazole were obtained additionally under purely thermal conditions 244). N/H insertion also takes place at benzimidazole 245 a). The reaction is thought to begin with formation of an N3-ylide, followed by N1 - C proton transfer leading to the formal N/H insertion product. Diazomalonic raters behave analogously however, they suffer complete or partial dealkoxycarbonylation under the reaction conditions 244) (Scheme 34). N-alkylation of imidazole and benzimidazole by the carbenoids derived from co-diazoacetophenone and 2-(diazoacetyl)naphthalene has also been reported 245 b>. 

Scheme 7.21 Copper(ll)-mediated N-arylation of polymer-bound benzimidazole.

Arylations of amines and nitrogen-containing heterocycles require the presence of a copper catalyst, usually 10% copper(ll) acetate. For example, the reaction of 4-MeC6H4Pb(OAc)3 with the benzimidazole 20 affords the arylation product 21 in 98% yield.39 40 Similarly, the arylation of the amino groups of heteroaromatic compounds 22 and 23 gives rise to the corresponding products 24a and 25 in good to excellent yields (Equations (7)-(9)).41 42... 

Azole compounds such as benzotriazole, benzimidazole, indazole and imidazoles are efficient anti-corrosion agents for copper and copper-base alloys [1-10]. Many experimental techniques [11-15] have been used to study the corrosion inhibition mechanisms, however, the mechanisms are still not well understood. It is believed that the complex formation between copper and nitrogen atoms would inhibit oxygen adsorption on copper surface [16-20]. 

Photolysis as well as thermolysis (150°C, copper-catalyzed) of (79) results in quantitative loss of CO2 (Scheme 29). The 1,3-dipole (80) cyclizes to the benzimidazole (81) or is intercepted by dipolarophiles like benzonitrile or by an alcohol (Scheme 29) <68TL325>. Other oxadiazolones of type (79) fragment to CO2, a nitrile, a nitrene, and a carbene finally leading to a host of products <79JCS(P1)483>. 

Numerous other examples of reactions of this type have been described and a particularly dramatic example of a product derived from oxygen atom transfer to a co-ordinated ligand is seen in the reaction of the benzimidazole ligand 9.16 with dioxygen in the presence of a copper(i) catalysts. The isolated product of the reaction is the copper(n) complex of the benzimidazole-3-carboxylic acid, 9.17. 

N-Arylation of various azoles (or their anions) was readily accomplished with p-tolyllead triacetate in the presence of copper(II)acetate [95JOC5678] however, die applicability of this procedure to other aryllead triacetates was not discussed. Solvent-dependent palladium-mediated allylations [95JHC1325] and Mitsunobu-based asymmetric alkylations [95JOC2008] of imidazoles and benzimidazoles have also been reported. 

More recently, Iiu et al. reported that a variety of non-chiral amphiphilic diacetylenes, non-chiral barbituric acids or amphiphilic aryl-benzimidazoles self-assemble into chiral clusters at the air/water interface or on aqueous solutions containing Ag+ ions, as demonstrated by CD measurements [108-111]. The chiral macroscopic conformational morphology of the polymers generated from copper salts of non-chiral monomers was imaged after their transfer onto solid support [ 112,113]. 

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D-Xylo-benzimidazole has also been prepared20 by the usual reaction at 135°, although the product was not identified correctly until later.22 Its isolation was first accomplished through precipitation as the copper salt, a procedure described by Moore and Link18 that is adaptable to the isolation of other readily water-soluble benzimidazoles. 

The benzimidazoles, as we have seen, are weak bases that are soluble in aqueous acids but may be precipitated from them by the addition of a stronger base such as ammonium hydroxide. The benzimidazoles are amphoteric substances, with acidic properties also, as shown by the formation of copper, silver, and other insoluble salts they are soluble in an excess of a strong base such as sodium hydroxide and may be precipitated from solution in that base by the addition of carbon dioxide. 

Copper (11) benzimidazole Azide, [Cu(C7H6N2)]-(N3)2 brn solid, decomposes explosively at... 

A variety of azole derivatives reacted with />-tolyllead triacetate 58 in the presence of copper diacetate to afford the iV-monoaryl derivatives in good to excellent yields (Equations (82)—(84)). 106 106a 109 109a 110 Benzimidazole 80 was arylated in 98% yield by />-tolyllead triacetate. In the case of the 5-aminobenzimidazole 81, excellent chemoselec-tivity was observed in favor of the primary aromatic amine with exclusive formation of the iV-/>-tolylaminobenzimi-dazole 82 in 50% yield.110... 

Direct palladium-catalyzed GG bond formation can be achieved between A -methy 1 imidazo 1 e and an aryl halide with selectivity for the more electron-rich C(5) position (Scheme 162) if C(5) is already substituted, then C(2) is preferred. iV-Methylbenzimidazole can be similarly arylated by various aryl iodides at the 2-position when catalyzed by copper(I) iodide to give excellent yields <1998BCJ467>. Rhodium can also catalyze direct C(2) arylation of N-alkyl benzimidazoles <20040L35>. 

Several different methods of synthesis of benzimidazoles have been reported. Intramolecular aryl guanidinylation of aryl bromides 103 with copper- and palladium-catalyzed methods led to... 

The utility of microwaves in the copper catalysed protocol for N-arylation using high molecular weight poly(ethylene glycol) (PEG 3400) as a solvent was explored by Colacino et al. [17] for accessing the N-arylated benzimidazole (vi) in presence of cuprous oxide, cesium carbonate and PEG 3400 under microwave activation, with no supplementary ligands. 

Oxidation (with such reagents as iron(III) chloride, potassium dichromate, silver oxide or nitrous acid) of 4,7-, 6,7-, and 5,6-dihydroxy-, and 5,6-dimethoxy-benzimidazoles gives the corresponding quinones. A 5-methyl group is oxidized by permanganate to carboxy (74CRV279). In the presence of copper(II)-piperidine or -dimethylamine complexes oxygen... 

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