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6926993 
Journal Article 
Boric Acid-Catalyzed Direct Condensation of Carboxylic Acids with Benzene-1,2-diamine into Benzimidazoles 
Maras, N; Kocevar, M; , 
2011 
Yes 
Helvetica Chimica Acta
ISSN: 0018-019X 
WILEY-V C H VERLAG GMBH 
WEINHEIM 
94 
10 
1860-1874 
English 
WOS:000297245500016 
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.