Imidazoles cross-coupling reactions

Apart from imidazol-2-ylidene carbenes, other electron-rich carbenes such as (L27)—generated by deprotonation of a 4,5-dihydroimidazole—have been tested for cross-coupling reactions, but gave much poorer results. The only reported exception is in the cross-coupling of arenediazonium salts with arylboronic acids, in which (L27) (used as hydrochloride) proved to be efficient.369... 

The synthesis and chemistry of pyrazoles, imidazoles, and 1,2,3-triazoles were actively pursued in 2006. A review on the cross-coupling reactions on azoles with two and more heteroatoms for pyrazoles and imidazoles has been published <06EJO3283>. Publications relating to 1,2,4-triazole and tetrazole chemistry were not particularly well represented this year. The solid-phase and combinatorial chemistry of these ring systems have not been investigated compared to past years. No attempt has been made to incorporate all the exciting chemistry or biological applications that have been published this year. 

Major advancements in the chemistry of pyrazoles, imidazoles, triazoles, tetrazoles, and related fused heterocyclic derivatives continued in 2000. Solid-phase combinatorial chemistry of pyrazoles and benzimidazoles has been particularly active. Synthetic routes to all areas continue to be pursued vigorously with improvements and applications. Notably, metal-promoted and cross-coupling reactions of all classes seemed to be a dominant theme in 2000. Applications of pyrazole-, imidazole-, and 1,2,3-benzotriazole-containing reagents to a wide array of synthetic applications remained active. 

For example, via cross-coupling reactions arylated imidazoles, which are otherwise difficult to prepare from imidazoles, can be prepared in a direct reaction. 

Nevertheless, there are certainly a number of painful limitations. There is no simple and efficient method for the synthesis of unsymmetrical N,N -diaryl-substituted imidazolium salts, very desirable compounds. Furthermore, the Buchwald-Hartwig-like cross-coupling reaction of N-monosubsti-tuted imidazoles with arylhalides, which would result in the formation of imidazolium salts, has not been reported yet. However, unsymmetrical N,N -... 

Other heteroaryl halides may be used in the Pd-catalyzed cross coupling reaction. Senanayake and co-workers reported the reaction of a chlorobenz-imidazole and a primary amine to synthesize the antihistamine norastemizol [34, 87]. The key Pd-catalyzed coupling reaction proceeded in 85% isolated yield using 0.5 mol% Pd, Eq. (160). During these investigations, the Sepracor group also noted that primary amines reacted preferentially over secondary amines. 

Deleuze-Masquefa et al. [15] showed that the microwave assisted bimolecular condensation of 2-imidazole carboxylic acid, followed by coupling with ortho-fluoroaniline and subsequent substitution on imidazole ring by Suzuki cross-coupling reaction gave the imidazo[l,2-a]quinoxaline (xiii) analogues in good yields. All the synthesized compounds showed high activities when evaluated for antitumor activities. 

Imidazoles and fused-derivatives have participated in a myriad of cross-coupling reactions. 2-Thiomethylrmidazolm-5-one 102 underwent efficient palladium-catalyzed cross-coupling reactions with boronic acids in the presence of copper(l)thiophene-2-carboxylate (CuTC) to give... 

Diarylimidazoles were prepared by Suzuki cross-coupling reactions of imidazole halides with arylboronic acids <05H(65)1975>. Suzuki cross-coupling reactions of 6-bromoimidazo[l,2-a]pyridines have been developed <05H(65)2979>. Cul-catalyzed iV-arylation of imidazoles and benzimidazoles with aryl bromides was achieved in a near-homogeneous system that utilized tetraethylammonium carbonate as base, 8-hydroxyquinoline as ligand and water as cosolvent <05JOC10135>. 

Boronic acid 137h was generated and used directly in Pd-catalyzed cross-coupling reaction leading to an imidazole-substituted indole... 

Zhang, C., Huang, J., Trudell, M.L., Nolan, S.P., PaIladium-imidazol-2-yhdene complexes as catalysts for facile and efficient Suzuki cross-coupling reactions of aiyl chlorides with aiylboronic acids, J. Oig. Chem. 1999, 64 3804-3805. 

Cross-coupling reactions and direct C—H arylations of imidazoles were disclosed. 2-Imidazolylpyridines 67 were synthesized from 2-bromopyridines 66 in the presence of potassium carbonate neat at high temperatures... 

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