Boric Acid-Catalyzed Direct Condensation of Carboxylic Acids with Benzene-1,2-diamine into Benzimidazoles

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 a...

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Bibliographic Details
Published in:Helvetica chimica acta 2011-10, Vol.94 (10), p.1860-1874
Main Authors: Maraš, Nenad, Kočevar, Marijan
Format: Article
Language:English
Subjects:
Benzimidazoles
Boric acid
Catalysis
Cyclocondensation
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Summary: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.
ISSN:0018-019X
1522-2675
DOI:10.1002/hlca.201100064