Imidazoles copper catalyzed synthesis

Regarding the limitations with the copper-promoted systems, palladium-catalysts were explored and applied in benzimidazole synthesis as well. In 2011, You and co-workers developed a palladium-catalyzed synthesis of 1,2-disubstituted (hetero)aiyl fused imidazoles from 1,2-dihaloarenes. This palladium-catalyzed cascade amination allows regiospecific and modular synthesis of a library of structurally diverse 1,2-disubstituted (hetero)aiyl fused imidazoles in good to excellent yields (Scheme 2.18). The prepared... 

N-Arylations of several other heterocycles have also been accomplished, including mono- and diarylation of imidazoles to form N-aryl imidazoles and imidazolium ions, respectively, which was extended to the synthesis of bis (N-heterocyclic) ligands [101, 102]. Pyridinium triazolinone ylides were obtained by a one-pot copper-catalyzed carboxygenation and chemoselective N-arylation of triazolopyridines with aryl(mesityl)iodonium salts (Scheme 6a) [103]. 

A practical copper-catalyzed method for the synthesis of imidazoles with this challenging substitution pattern has been developed [99]... 

Fu et al. developed an efficient Cu(OAc)2-catalyzed synthesis of imidazobenz-imidazole derivatives via aerobic oxidative intramolecular C(sp )-H amination in excellent yields (Scheme 8.55). 1,10-Phenanthroline was chosen as the ligand and NaOAc was used as the base. Molecular oxygen acts as the oxidant to recycle the copper catalyst [95]. Kaliappan and coworkers reported an efficient, one-pot, copper-catalyzed C(sp )-H cascade amination to synthesize various imidazobenzimidazole derivatives from various azoles and aryl bromides or 2-bromopyridines [96]. 

Bromo- and iodoimidazoles are useful intermediates for further functionalization. 4(5)-Aryl- I //-imidazoles 57 can be efficiently and selectively prepared by palladium-catalyzed Suzuki-Miyaura reaction of commercially available 4(5)-bromo-l//-imidazole 56 with arylboronic acids under phase-transfer conditions, which then underwent highly selective palladium-catalyzed and copper(I) iodide mediated direct C-2-arylation with a variety of aryl bromides and iodides under base-free and ligandless conditions to produce 2,4(5)-diaryl-l//-imidazoles 58 in modest to good yields <07JOC8543>. A new procedure for the synthesis of a series of substituted 2-phenylhistamines 60 utilizing a microwave-promoted Suzuki... 

Arylations. Copper(II) acetate catalyzes the reaction of arylboronic acids with phenols and amines (including imidazole and amides) to provide diaryl ethers (e.g., for synthesis of thyroxine) and arylamines, respectively. The reactions are quite erratic, although some preparatively useful cases have been found. 

Metal-mediated approaches to the synthesis of imidazoles have been reported. PaUadium(ll)-catalyzed intermolecular 1,2-diamination of conjugated dienes with ureas led to 4-alk enyl-2-imidazolones in good yields rmder mild conditions <05JA7308>. Palladium-catalyzed cyclization of O-pentafluorobenzoylamidoximes 74 furnished l-benzyl-2-substituted-4-methylimidazoles 75 <050L609>. Direct copper(I)-chloride mediated reaction of nitriles 76 with a-amino acetals 77 followed by acidic reaction led to a variety of 2-substituted imidazoles 78 <05TL8369>. 

Reddy VP, Kumar V, Rao KR (2010) Copper oxide nanoparticles catalyzed vinylation of imidazoles with vinyl halides under ligand-free conditions. Tet Lett 51 3181-3185 Dandia A, Parewa V, Rathore KS (2012) Synthesis and characterization of CdS and Mn doped CdS nanoparticles and their catalytic application for chemoselective synthesis of benzimidazoles and benzothiazoles in aqueous medium. Catal Comm 28 90-94 Itoh T, Nagata K, Ishikawa H, Ohsawa A (2004) Synthesis of 2-arylbenzothiazoles and imidazoles using scandium triflate as a catalyst for both a ring closing and an oxidation steps. Heterocycles 63 2769-2783... 

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