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Boric Acid‐Catalyzed Direct Condensation of Carboxylic Acids with Benzene‐1,2‐diamine into Benzimidazoles
Author(s) -
Maraš Nenad,
Kočevar Marijan
Publication year - 2011
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.201100064
Subject(s) - chemistry , boric acid , benzene , catalysis , diamine , benzoic acid , phenylboronic acid , organic chemistry , condensation , toluene , xylene , carboxylic acid , medicinal chemistry , physics , thermodynamics
The applicability of boric acid catalysis for the direct condensation of carboxylic acids with benzene‐1,2‐diamine to give 2‐substituted benzimidazoles was investigated. It was found that catalytic amounts (5–10 mol‐%) of boric acid efficiently promote the cyclocondensation of aliphatic carboxylic acids in refluxing toluene. In addition, the relatively neutral conditions allow the use of acid‐sensitive substrates and give rise to specific transformations and selectivities that are not observed with some classical methods. Benzoic acids were found to be less reactive than aliphatic acids and thus require refluxing xylene for better efficiency. Phenylboronic acid was found to be inactive as a catalyst due to its rapid consumption by condensation with benzene‐1,2‐diamine to give a 2‐phenylbenzodiazaborole.