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IJC-B Vol.46B [2007] >
IJC-B Vol.46B(05) [May 2007] >
| 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 |
| Source: | IJC-B Vol.46B(05) [May 2007]
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