Benzimidazole 2-amino-, oxidation

Mit dem Dinatriumsalz von Cyanamid wird 3-Amino-1,2,4-benzotriazin-l,4-bis-oxid (81 %)320 gebildet, mit Cyan-acetamid hingegen 2-Aminocarbony -l-hydroxy-benzimidazol-3-oxid (78%)321 [analog reagieren 1-Nitro-alkane322-324 und (3-Oxo-alkyl)-sulfone]325 ... 

The reaction of iV-(2,4-dinitrophenyl)amino acids with base in aqueous dioxane has been shown to give benzimidazole iV-oxides (7). The rate-determining step is likely to be formation of an iV-alkylidene-2-nitrosoaniline intermediate (6), which is followed by rapid cyclization and decarboxylation.19 The loss of carbon dioxide from perbenzoate anions has been investigated by mass spectrometry and electronic structure calculations. The results, including isotopic labelling experiments, support a mechanism involving initial intramolecular nucleophilic attack at either the ortho- or ipso-ring positions. They also indicate that epoxides may be intermediates en route to the phenoxide products.20 There has also been a theoretical study of the formation of trichlorinated dibenzo-/ -dioxins by reaction of 2,4,5-trichlorophenolate ions with 2,4-dichlorophenol.21... 

Benzimidazoles, 2,3-dihydro-, by Nu addition at C-2, 56, 203 Benzimidazole, 2-fluoro-, 59, 272 Benzimidazole, 1-methyl-, ring expansion to chloroquinoxalines, 59, 305 Benzimidazole, l-methyl-2-(5 -methyl-2 -thienyl)-, bromination, 57, 319 Benzimidazole 3-oxides, chloro-deoxygenation, 59, 270 Benzimidazoles, 2-perfluoroalkyl-, 60, 25 Benzimidazoles, 2-(l-pyridinio)-, 60, 204 Benzimidazoles, 2-(2-pyridinioethyl)-, elimination reactions, 60, 246 Benzimidazoles, tetrafluoro-, 59, 14 Benzimidazole-2-carboxylic ester 3-oxide, 7-nitro-5-trifluoromethyl-, 60, 17 Benzimidazolium salts, l-amino-3-alkyl-, reaction with activated acetylenes, 56, 138... 

Benzimidazol-3-oxid 2-Cyan-5-nitro-E8c, 227 [(2,4-(N02)2—Ar] — NH — CH2— CN/Base 2,1-Benzoxazol 3-Amino-5-cyan-... 

Benzimidazol-3-oxid 2-Ethoxycarbo-nyl-5-methoxy- E8c, 227 [(4-OCH3 - 2-N02 - Ar) - NH -CH2-COOR + Na-OR] 2-Benzofuran 5-Amino-l-(l-nitro-propyl)-3-oxo-l, 3-dihydro-iV/lc, 513... 

H). The use of sodium borohydride in the presence of platinum, palladium or Raney nickel [96] has been shown to give greater than 50% yields of benzimidazole )V-oxides, but even this reagent is capable of reducing a nitro group to amino, and combined with product loss on work-up, yields of the Af-oxides are often disappointing [97]. Sulfide reduction procedures (c.g. ammonium sulfide) seem better for 1-substituted benzimidazole 3-oxides than for benzimidazole 1-oxides [88, 92]. 

There are a number of methods which cyclize o-amino- or o-nitroarylamincs to benzimidazoles or benzimidazole A -oxides. These include cases where one of the amino groups is a secondary or a tertiary amine. 

In view of the observation that A-o-nitrophenyl derivatives of glycine and other a-amino acids could be converted into benzimidazolones by the action of heat, and the assumption that iV-oxides were intermediates in the thermolysis [156], it was thought tliat flash vacuum pyrolysis with a very short reaction time might allow isolation of the IV-oxides. This approach, however, did not turn out to be as synthetically efficient as the base treatment method [97]. Indeed, heating such compounds in sand at 200° C is probably of more use for making benzimidazoles or benzimidazolones [156]. Benzimidazole iV-oxides can be made from acid-catalysed thermal or photochemical reactions of AyV-dialkyl-o-nitroanilincs, but not from purely thermal reactions. 

Dinitro-r-anilines constitute a major group of pre-emergent herbicides. The photodecomposition of these herbicides has been simulated by studying the photolysis of one typical example, Trifluralin 47 (74MI1). The major product from the action of sunlight in aqueous alkaline media was the benzimidazole 48, and the by-products included the dihyroxybenzimidazo-line 49, the benzimidazole Y-oxide, and benzimidazoline derivatives of 48, all being derived by r-amino-effect chemistry (Scheme 17). 

There are general reviews on heterocyclic syntheses by cycloaddition reactions of isocyanates and on the use of heterocyclic cations in preparative organic chemistry. More specific topics are 5-hydroxymethylfuran-2-carb-aldehyde, isobenzofurans and related ort/io-quinonoid systems, the conversion of 2//-cyclohepta[Zj] furan-2-one (1) into derivatives of azulene, the synthesis of indoles from o-alkylphenyl isocyanides, and abnormal Fischer indolization reactions of o-methoxyphenylhydrazones. Two reviews on isoindoles have appeared and a lecture on highly conducting charge-transfer complexes that are based on heterocyclic selenium and tellurium donors has been reprinted.Recent advances in the chemistry of imidazole and in the use of nitro-imidazoles as radiosensitizers have been summarized. There have been reviews on benzimidazole A -oxides and on dihydrobenzimidazoles, benzimidazolones, benzimidazolethiones, and related compounds. Other topics are synthetic applications of 1,3-dithiolium and 1,3-oxathiolium salts and of isoxazoles, the chemistry of benzisoxazoles, 2-amino-oxazoles, 5-oxazolones (2), furoxans, benzofuroxans, and related systems, the synthesis of five-membered meso-ionic compounds, and tetrazoles. ... 

H-Benzimidazole, 2,2-pentamethylene-reduction, 5, 423 Benzimidazole-2-carbaldehyde oximes, 5, 436 Benzimidazolecarbaldehydes oxidation, 5, 437 Benzimidazole-2-carbamates 5-substituted as anthelmintics, 1, 202 Benzimidazole-1-carboxylic acid, 2-amino-methyl ester reactions, 5, 453... 

Carbodiimides are rapidly and conveniently obtained from thioureas (Table 10.14) [19], whereas 2-amino- and 2-hydroxyphenylthioureas are oxidatively cyclized to benzimidazoles and benzoxazoles, respectively (Scheme 10.2). 

Photolytic. Irradiation of trifluralin in hexane by laboratory light produced a,a,a-trifluoro-2,6-dinitro-A-propyl-jo-toluidine and a,a,a-trifluoro-2,6-dinitro-p-toluidine. The sunlight irradiation of trifluralin in water yielded a,a,a-trifluoro-A, 7 -dipropyl-5-nitrotoluene-3,4-diamine, a,a,a-trifluoro-A/ ,A/ -dipropyltoluene-3,4,5-triamine, 2-ethyl-7-nitro-5-(trifluoromethyl)benzimidazole, 2,3-dihydroxy-2-ethyl-7-nitro-l-propyl-5-(trifluoromethyl)benzimidazoline, and 2-ethyl-7-nitro-5-(trifluoromethyl)benzimidazole. 2-Amino-6-nitro-a,a,a-trifluoro-p-toluidine and 2-ethyl-5-nitro-7-(trifluoromethyl)benzimidazole also were reported as major products under acidic and basic conditions, respectively (Crosby and Leitis, 1973). In a later study, Leitis and Crosby (1974) reported that trifluralin in aqueous solutions was very unstable to sunlight, especially in the presence of methanol. The photodecomposition of trifluralin involved oxidative TV-dealkylation, nitro reduction, and reductive cyclization. The principal photodecomposition products of trifluralin were 2-amino-6-nitro-a,a,a-trifluoro-jo-toluidine, 2-ethyl-7-nitro-5-(trifluoromethyl)benzimida-zole 3-oxide, 2,3-dihydroxy-2-ethyl-7-nitro-l-propyl-5-(trifluoromethyl)benzimidazole, and two azoxybenzenes. Under alkaline conditions, the principal photodecomposition product was 2-ethyl-7-nitro-5-(trifluoromethyl)-benzimidazole (Leitis and Crosby, 1974). 

Substituenten in 2-Stellung bestimmen bei der Blei (IV)-acetat-Oxidation von 1-Amino-benz-imidazolen, welche Produkte entstehen. Das intermediar gebildete Nitren dimerisiert entweder zum Tetrazen oder lagert sich zura 1,2,4-Benzotriazin um. Nur heim unsubstituierten 1-Amino-benzimidazol selbst lauft die Oxidation weiter und das Tetrazen wird zu 1-Acetyl-benzimidazol gespalten534 z.B. ... 

Die Oxidation von 1-Amino-5,6-dimethy]-l,5-dihydro- mit Blei (IV)-acetat fiihrt unter Abspaltung von Stickstoff zu l, 2-DimethyI-5,6-dehydro-benzimidazol, das mit verschiedenen Dienen abgefangen werden kann655 z.B. ... 

Oxidation of 1-aminobenzimidazoles with manganese dioxide or lead tetraacetate can give either 1,1 -azobenzimidazoles (735) or 3-substituted benzo-l,2,4-triazines (736). Electrochemical measurements have shown that the first step in this reaction is removal of an electron from a ir-orbital of benzimidazole rather than from the A-amino group. Because the cation radical which is formed must be stabilized by loss of a proton, for (736) to form the 2-substituent must contain an NH or OH group. This is unnecessary for the formation of the azo product (735) which may form via a nitrene intermediate. 

Crystalline benzimidazoles have been obtained from all aldonic acids so far tested with only one exception that is known to the writer. Lohmar and Link29 reported that the condensation of D-glucosaminic acid (= 2-amino-2-desoxy-D-gIuconic acid) with o-phenylenediamine under a variety of conditions failed to yield a crystalline product. The direct oxidative condensation of D-glucosamine hydrochloride with o-phenylenediamine in the presence of cupric acetate yielded only the known 2-(D-arofro-tetrahydroxybutyl)quinoxaline (III) and not the desired benzimidazole. 

Oxidation of 2-amino-3-cyanobenzodiazepinium chloride with hydrogen peroxide in the presence of peroxidase as a catalyst gave benzimidazole, which, unlike the benzodiazepine, was fluorescent, and this reaction has been applied to the determination of hydrogen peroxide by fluorimetry (80CPB2325). 

Oxidation of 2-amino-3-cyanobenzodiazepinium chloride with hydrogen peroxide in the presence of peroxidase as a catalyst gave a benzimidazole (80CPB2325). 

Pyrimidin 6-Amino-2,4-dioxo-3-phenyl-l,2,3,4-tetrahydro- E15/2, 2228 [ —R—OH(Cyclokond.)] lH- 6-Nitro-2,3-dihydro- IV/la, 182 Quinolin 4-Hydrazino-6,7-methylen-dioxy- E16a, 700 (Cl - NH-NH2) Quinolin-l-oxid 2-Amino-3-aminocarbonyl- E7a, 504 [2-N02 - Ar -CH = C(CN) -CO —NH2/Pt]... 

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