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Title: Synthesis of 2-indolylbenzimidazoles using Fischer’s indole method
Authors: Dubey, P K
Babu, Balaji
Narayana, M Venkata
Keywords: Indoles;Benzimidazoles;Philip’s conditions;TEBAC;PTC
Issue Date: May-2007
Publisher: CSIR
IPC Code: Int.Cl.⁸ C07D
Abstract: Condensation of phenylhydrazine 5a (i.e. 5, R²=H) with 2-acetylbenzimidazole 3 in the presence of catalytic amount of acetic acid in refluxing methanol gives phenylhydrazone derivative 6a (R²=H) of 2-acetylbenzimidazole, which on heating with the polyphosphoric acid (PPA) yields 2-(1H-2-indolyl)benzimidazole 7a (i.e. 7, R²=H). 7 is alkylated using different alkylating agents under phase transfer catalyzed conditions using K₂CO₃ as a base and DMF as a solvent to give 2-(1H-indolyl)-1-substituted benzimidazoles 9. The latter can also be prepared by alkylation of 3 giving 4, followed by condensation with phenylhydrazine 5, yielding 8 and the subsequent cyclization with PPA. Alternatively, 9 can also be prepared by treating indole-2-carboxylic acid 10 with o-phenylenediaminosulphate 1a. H₂SO₄ (i.e. 1, where R¹=H) in refluxing ethylene glycol yielding 7a, followed by alkylation of the product under DMF/ K₂CO₃ /TEBAC conditions. Once again, treatment of N-substituted o-phenylenediaminosulphate 1b (i.e. 1, R¹=Me) with 10a/10b in refluxing ethylene glycol results in the formation of 9a/9d. 3 itself is obtained by acidic dichromate oxidation of 2-(⍺-hydroxy)ethylbenzimidazole 2, which in turn is obtained from o-phenylenediamine 1a (i.e. 1, where R¹=H) and lactic acid under Phillip’s conditions.
Page(s): 823-828
ISSN: 0376-4699
Appears in Collections:IJC-B Vol.46B(05) [May 2007]

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