2- Arylbenzimidazoles

Dehydration (cf., 6, 648). A reagent (1), prepared in situ from (C6H5),PO and Tf20 in the molar ratio 2 1, effects dehydration, usually at 25°, of amides or oximes to nitriles in >90% yield. It also effects condensation of acids and amines to form amides. The reaction of an aryl carboxylic acid with an o-phenylenediamine promoted by 1 provides 2-arylbenzimidazoles in >80% yield (equation I). If the... 

Several examples of oxidative ring closures by attack on an azomethine group by an amine have been reported78 thus arylidene-o-phenylenedi-amines (32) have been oxidized to 2-arylbenzimidazoles (33) [Eq. (35)]. 

The electrochemical behavior itself 5(6)-nitrobenzimidazole is investigated depending on media pH by classical polarography [992-994], constantly current, and variable current [995, 996], The reduction 5(6)-nitro-2-arylbenzimidazoles is carried out in DMF and H20/DMF media [997], The polarography was utilized in a study of the influence of 5(6)-nitrobenzimidazole on corrosion-electrochemical behavior of chromos steel [998],... 

Perry RJ, Wilson BD (1993) A novel palladium-catalyzed synthesis of 2-arylbenzimidazoles. J Org Chem 58 7016-7021... 

Savall BM, Eontimayor JR (2008) Synthesis of 2-arylbenzimidazoles via microwave Suzuki-Miyaura reaction of unprotected 2-chlorobenzimidazoles. Tetrahedron Lett 49 6667-6669... 

Arylquinoxalines 28 are obtained in a one-pot condensation reaction of 3-arylisoxazol-5(4f/)-ones and benzene-1,2-diamines in good yields. 2-Arylbenzimidazoles are formed as minor products. ... 

When an o-nitroaniline is acylatcd by ethyl chloroformate and then catalyti-cally reduced, thermolysis of the reduction product (33) gives a 1-substituted 2-benzimidazolone (34) (Scheme 2.1.15) f99J. Presumably the carbamates (33) eliminate ethanol as they cyclize. and so the reactions bear similarities to those which proceed through isocyanates (see Scheme 2.1.18). In the presence of magnesium chloride, which appears to activate the urea carbonyl group to solvolysis and condensation, some benzimidazolones are converted into 2-alkyl- and 2-arylbenzimidazoles [100],... 

A novel palladium-catalysed carbonylation of iodobenzene has recently been linked to base-induced coupling and cyclization with o-phenylenediamine, to give 2-arylbenzimidazoles without having to use an aryl carboxylic acid (Scheme 3.1.13). Provided that bases with pATa values around 6.6 are used, the yields of 2-arylbcnzimidazoles lie in the range 70-98%. This route is tolerant of a variety of functional groups and complements the classical approaches where the required benzoic acids arc not readily available [85]. 

Imines 1110 derived from trifluoromethyl aryl ketones and orT o-phenylenediamines 1109 undergo intramolecular cyclization to afford 2-arylbenzimidazoles 1111. The reaction is carried out under basic conditions and the CF3 group serves as a leaving group (Scheme 268) <1999TL4119>. 

Since the nature of the substituent present at position 2 of a 5(6)-substituted benzimidazole plays a significant role in determining the anthelmintic profile of the resulting molecule, a variety of structural modifications have been carried out at this site to arrive at a definite structure-activity relationship. Consequently, a series of 2-alkyl and 2-arylbenzimidazoles have been synthesized by condensation of o-phenyl-... 

THF models transfer their C-2 fragment in between 1,4- or 1,5-binucleophilic sites to generate five- or six-membered rings. The acid-catalyzed reactions of 2-aryloxazolidines and oxazinanes with o-aminobenzamide, o-aminothiophenol, and o-phenylenediamine give 2-aryl-4( 1 //)-quinazolinones 69, 2-arylthiazoles, and a mixture of 2-arylbenzimidazole and l-benzyl-2-arylbenzimidazole 68, respectively. Whereas benzothiazole and benzimidazole could be formed by air oxidation of their initially formed dihydro derivatives, l-benzyl-2-phenylbenzimidazole, as formulated below, could arise from initially formed diimine, its cyclization, and subsequent 1,3-hydride shift (88JCR(S)322, 89IJC(B)802). It is the sole product when o-phenyl-enediamine and the model are used in 1 2 stoichiometry. 

In the presence of copper(I) chloride in pyridine N-benzylidene-o-phenylenediamines 20 undergo catalytic oxidative dehydrogenation with 0 to afford 2-arylbenzimidazoles 21 or 2,2 -diaryl-1,1 -... 

Joshi, R. S., Mandhane, P. G., Dabhade, S. K. and Gill, C. H. 2010. Tetrabutylammonium fluoride (TBAF) catalysed synthesis of 2-arylbenzimidazole in water under ultrasound irradiation. 7. Chin. Chem. Soc. 57 1227-1231. 

Skraup synthesis. It has now been reported that a convenient and cost effective preparative method results by using silver-loaded titania as the photocatalyst. In a similar way, n-nitroanilines are reduced to 1,2-phenylendiamines on Pt-loaded Xi02. Under these conditions condensation and dehydrogenation ensue leading to 2-arylbenzimidazoles in a convenient one-pot procedure that combines catalysis and photocatalysis (see Scheme 4). °... 

Sahu, D. P. Iodine-mediated synthesis of 2-arylbenzoxazoles, 2-arylbenzimidazoles, and 1,3,5-tiisub-stituted pyrazoles. Synth. Commun. 2006, 36, 2189-2194. 

An efficient and simple synthesis of several 2-arylbenzimidazoles from the reaction of 4-methyl-l,2-phenylenediamine and aromatic carboxyhc acids in the presence of zeolite catalyst is reported. The reactions were performed nnder MW irradiation, and the catalyst could be recycled and used for several times [103] (Scheme 3.43). 

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