Benzimidazole 3-oxides

The reactivity of these compounds is somewhat similar to that of the azolonium ions, particularly when the cationic species is involved. However, although the typical reaction is with nucleophiles, the intermediate (20) can lose the iV-oxide group to give the simple a-substituted azole (21). Benzimidazole 3-oxides are readily converted into 2-chloroben-... 

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 fV-oxide oxygen (191 -> 192). 

Nitro-l-isothiocyanato-benzol wird reduktivzu2-Mercapto-benzimidazol-3-oxid cy-clisiert3 ... 

Ethyl-7-nitro-5-(trifluoromethyl)benzimidazole-3-oxide, see Trifluralin 5-Ethyl parathion, see Parathion 0,0-Ethyl-O-phosphorothioate, see Chlorpyrifos, Diazinon. Ronnel... 

Die UV-Spcktren der tautomeren Benzimidazol-3-oxide sind pH- und Losungsmittel-abhangig. Die charakteristische Absorption der neutralen oder kationischen Benzimidazol-3-oxide wird im Bereich von 280-300 nm (c = 7000-20000) beobachtet, die Anionen absorbieren bei hoheren Wcllcnlangen (330-400 nm)696. 

Nitro-anilin Reaktionsbe-. .. -benzimidazol-3-oxid Ausbeutc Schmp. Lite-... 

R = ch3 /-(l-Carboxy-ethyl)-5-chlor-benzimidazol-3-oxid 81% Schmp. 197-202° r = ch2—CH2—sch, l-(l-Carboxy-3-methylthio-propyl)-... 53% Schmp. 218-222 ... 

Die analoge Umsetzung von Benzaldehyd-phenylnitronen mit Benzofuroxanen ergibt 2-Aryl-l-hydroxy-benzimidazol-3-oxide. Aufgrund der l-Hydroxy-3-oxid-Tautomerie sind 5/6-Substituenten im Aryl-Teil nicht unterscheidbar185. 

Benzimidazol-3-oxide (s. S. 219, 227) liegen in einem tautomeren Gleichgewicht mit 1-Hydroxy-benzimidazolen vor. Ihre Reduktion gelingt u.a. mit Phosphor(III)-chlorid195 ... 

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. 

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 ... 

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

Benzimidazole 3-oxides, e.g., 276, react with phosphorus oxychloride or sulfuryl chloride to form the corresponding... 

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... 

Oxidation of certain heteroaromatic Y-oxides has been reported to give dimers of type C, e.g., the dimer (135b) obtained on heating an aqueous solution of benzimidazole 3-oxide in a sealed tube in the presence of oxygen.219 A similar 2,2 -dimer was formed when 2-(2-naphthyl)thioindoxyl-1,1 -dioxide was oxidized with bromine or potassium ferricyanide.220... 

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... 

Benzimidazol-3-oxid l-(l-Carboxy-3-methylthio-propyl)-5-chlor E8c, 292 [4-C1 — 2-NO -phenol/ CH20 + RS-(CH2)2-CH(NH2)-COOH]... 

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]. 

Tricyclic benzimidazole 3-oxides (60) made by heating various (59) in acid ... 

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