Studies on synthesis of 2-acetylbenzimidazole and related benzimidazole derivatives

Department of Chemistry, College of Engineering, J. N. T. University, Kukatpally, Hyderabad-500 072, India

Department of Chemistry, Dalhousie University, Halifax, N.S., B3H 4J3, Canada

Munuscript received 10 February 1998, revised 7 August 1998, accepted 18 November 1998

Condensation of a-phenylenediamine (1) with propanoic acid under Phillips' conditions gives 2-ethylbenzimidazole (2). Attempts to oxidise 2 to 2-acetylbenzimidazolc (3) using H₂O₂, SeO₂, KMnO₄ acetonc were unsuccessful. Condensation of 2 with benzaldehyde yields 2-(α-methybtyryl)benzimidazole (4) which on oxidation with KMnO₄ gives benzimidazole-2-carboxylic acid (5) as the sole product. Reaction of 1 with pyruvic acid results in 3-metbylhenzo-1H-dihydropyrazine-2-one (7) rather than 3 as the major product. Treatment of 1 with formic acid gives the known compound benzimidazole (9) which with acetic anhydride in the presence of NaOAc does not yield 3. Reaction of 1 with lactic acid under Phillips conditions gives 2-(α-hydroxyethyl)benzimidazole (10) which on oxidation with add dichromate, however, yields 3. Studies on syntheses and spectral properties of related benzimidazoles are reported.