1021422-09-2Relevant articles and documents
Synthesis of 2-indolylbenzimidazoles using Fischer's indole method
Dubey,Babu, Balaji,Venkata Narayana
, p. 823 - 828 (2008/09/18)
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 la. 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 lb (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-(α-hydroxy)ethylbenzimidazole 2, which in turn is obtained from o-phenylenediamine la (i.e. 1, where R1=H) and lactic acid under Phillip's conditions.
