Benzimidazole N-oxides

Tab. 10 Benzimidazol-N-oxide aus N-Alkyl-2-nitro-anilinen durch Cyclisierung...

D.M. Smith, Benzimidazole-N-Oxides, in P.N. Preston, Benzimidazoles and Congeneric Tricyclic Compounds, Kap.2, Wiley Interscience, New York 1981. 

Cyanations of benzimidazolium or benzimidazole N-oxides have been reported (93CHE127). Cyanopyrazoles are formed by irradiation of pyrazoles in the presence of cyanide ions in photosubstitution reactions. 

The chemistry of imidazole and benzimidazole N-oxides has been reviewed, and methods of preparation have been summarized (88JCS(Pi)68i, 93CHE127). The oxides are thermally unstable and may be explosive (84CB30, 89S773). 

Although the direct oxidation of the parent compounds with organic peracids has not proved fruitful, benzimidazole N-oxides can be made by the action of boiling hydrochloric acid on o-nitro-N, A-dialkylanilines, although prolonged treatment results in the formation of a chloro-substituted benzimidazole (B-73MI40800). 

Benzimidazol-N-oxide entstehen bei der Hydrierung von 2-Nitro-N-acyI-anilinen in aquimolarer athanolischer Salzsaure iiber Platin(IV)-oxid als einziges Reaktionsprodukt. Offensichtlich katalysiert die Saure die Cyclisierung des intermediar gebildeten Hydroxyl-amins derart, daB eine Rcduktion zum primaren Amin nicht stattfinden kann (ohne Sau-re-Zusatz werden primare aromatische Amine erhalten) ... 

S5mthesis of benzimidazole N-oxides on SynPhase Lanterns was discovered by Wu et al. [34] via tin(ll)-pro-moted reduction-cyclization of aryl nitro 3-keto methyl esters. The focal point of this synthesis involves the reduc-hon of an aryl nitro to a hydroxyamino intermediate, which subsequently condenses with an internal carbonyl group to produce benzimidazole N-oxide with minor quantity of benzimidazole as a side product (Scheme 12). 

SCHEME 12 SoKd-phase synthesis of benzimidazole N-oxides on SynPhase Lanterns. 

Z. Wu, N.J. Ede, M.N. Mathieu, Solid-phase synthesis of benzimidazole N-oxides on S)mPhase Lanterns, Tetrahedron Lett. 44 (2003) 2293-2296. 

Alternativ konnen derartige N-Oxide elektrochemisch reduziert werden71,448. Im Falle von 2-Cyan-benzimidazol-3-oxid wird durch verlangerte Elektrolysedauer zusatzlich eine Reduktion der Cyan-Gruppe erreicht448. 

Benzofurazan-l-oxid reagiert mit C,N-Diphenyl-nitron unter Bildung von l-Hydroxy-2-phe-nyl-benzimidazol-3-oxid (80%)334 ... 

In what appears to be a related reaction, benzimidazole Af-oxides give rise to ben-zimidazolinones as by-products when treated with an acyl halide in the presence of alkali. With tosyl chloride the sole product is the benzimidazolinone (111) which may be formed as in Scheme 50. The N rearrangement could also take place via the oxaziridine (112) <73JCS(P 1)705). 

In a Study of the formation of benzimidazoles by the peroxy acid-catalyzed cyclization of o-acylamino-iV,lV-dialkylaniIines, it has been demonstrated that the reaction proceeds via an iV-oxide intermediate, since it has proved possible to synthesize this N-oxide and cyclize it under the reaction conditions (B-73MI40800). Both ortho-N-acylated and -N-... 

Benzimidazole 3-oxides, e.g. (189), react with phosphorus oxychloride or sulfuryl chloride to form the corresponding 2-chlorobenzimidazoles. The reaction sequence involves first formation of a nucleophilic complex (190), then attack of chloride ions on the complex, followed by rearomatization involving loss of the N -oxide oxygen (191 192). 

A number of different A-oxides have been investigated polarographically, such as N-oxides of quinoline [421], acridine [422], pyrazine [423], benzimidazole [424], quinoxaline [415], phenazine [416], and adenine [425], and the influence of substituents was discussed. 

Chichibabin reaction, 5, 409-410 sulfonation, 5, 429 synthesis, 5, 160, 161, 457-498, 496 tautomerism, 5, 365 toxicity, 1, 139 UV spectra, 5, 356, 357 2H-Benzimidazoles 3,3-dioxides synthesis, 6, 407 JV,N -dioxides reactions, 5, 456 Benzimidazoles, aryl-oxidation, 5, 433 Benzimidazoles, nitro-mass spectra, 5, 359 reduction, 5, 441 Benzimidazole-2-sulfonic acids reactions... 

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