Benzimidazole acetylation

Benzimidazo[2,1 -a]isoquinolines synthesis, 5, 161 Benzimidazole, 1-acetyl-reactions... 

Treatment of 2-acetyl- or 2-formyl-benzimidazole 587 with hydrazines gave the corresponding hydrazones 588, which cyclized with ethyl chloro-formate to give [84JCR(S)384] triazinobenzimidazoles 589. 

With a-keto-N-arylhydrazidoylchlorides. The thiazolo[3,2-/z benzimidazole 373 was obtained by treating the 2-mercap-tobenzimidazole 371 with a-acetyl-iV-arylhydrazidoyl chloride 372 and NaOEt in refluxing ethanol (Equation 167)... 

Das UV-Spektrum von Benzimidazol weist drei Absorptionsbanden auf. Elektronen-Iiefcrnde Alkyl-Substituenten u. a. wirken bathochrom, derselbe Effekt wird auch im Basischen bei De-protonierung beobachtet. Protonierung sowie Elektronen-Akzeptor-Substituenten (z. B. Acetyl- oder Nitro-Gruppen) verursachen Hypsochromie667-677-695. 

Ausgehend von l-Acetyl-benzimidazol-5,6-dicarbonsaure-anhydrid isoliert man bei dcr Thermolyse mit Azido-trimethyl-silan ein 1 1-Isomcrengcmisch 1-Acetyl-6,8-dioxo-1,5,6,8-tetrahydro-( 1,3-oxazino[4,5-f benzimidazol )ll-Acetyl-5,7-dioxo-l,5,7 8-tetrahydro-(l,3-oxazino[5,4-f]benzimidazol, das ohne Reini-gung direkt mit Amiden (z. B. Formamidinacetat) umgesetzt werdcn kann540. 

Befindet sich das Acylierungsmittel allerdings in sterisch giinstiger Position, so kann der Angriff auch im Aryl-Teil stattfinden. Entsprechend cyclisiert das Benzimidazol I thermisch intramo-lekular zu 8-Acetyl-9-oxo-3-(4-chlor-phenyl)-6,9-dihydra-3H-(Jmidazo[4,5-f -chinolin) (II 63%) Schmp. > 360°)542 ... 

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. ... 

Habib and co-workers observed the rearrangement of 2-quin-oxalinone 4-oxides (219) on treatment with acetic anhydride to 1,3-diacetyl- or l-acetyl-3-acyl-2-benzimidazolones (220).219 Recently, the ring contraction of 2-azidoquinoxaline 1-oxide to 2-cyano-l-hydroxy-benzimidazole has been reported.220... 

In the reaction of a mixture of E- and Z-isomers of l-methyl-2-acetyl-benzimidazole oxime (31) in the KOH/DMSO system (90-95°C, atmospheric acetylene pressure, mass oxime 31/KOH/DMSO ratio 1 1 20, 3 hr), the pyrrole ring is formed only from the Z-isomer. Recovered oxime... 

The acetylation of 2-(D-ara6o-tetrahydroxybutyl)benzimidazole is reported to yield a tetraacetate 7 2-(D-paiacto-pentahydroxypentyl)-benzimidazole, on the other hand, apparently forms a hexaacetyl derivative,30 and the dibenzimidazole from D-mannaric acid, which contains four hydroxyl and two imino groups, forms a hexaacetyl derivative.22,28 It is not clear from these isolated cases whether N-acetylation as well as O-acetylation is to be expected or not. 

Some selected examples of 7c-barriers are given in Table XII. Conformational states of N-acetyl derivatives of pyrazole, imidazole, 1,2,3-triazole, 1,2,4-triazole, indole, benzimidazole, benzotriazole, indazole, and tetrazole have been studied by 13C NMR (78JCS(P2)99). In some cases, the occurrence of only one isomer precludes the determination of the barrier, as for 1-acetylpyrazole (74BSF1137) and 1-acetylindoles (750MR445). 

Preparation of /G(+)-3-A,-acetyl-2,3-dihydro-7-methyl-lH-pyrrolo[l,2-a] benzimidazole... 

Potential, chemotherapeutic activity of this class of compounds stimulated the synthesis313,337,352 of a series of benzimidazole-, pyrimidine-, and purine-substituted nucleosides of D-glucuronic acid derivatives, using, as the starting sugar-component, bromide 1 and methyl (2,3,4-tri-0-acetyl-D-glucopyranosylamine)uronate, respectively. 

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