Syntheses of Benzimidazoles, Quinoxalines and 3,3‐Dihydro‐1H‐1,5‐benzodiazepines Starting from o‐Phenylenediamine

A series of benzo‐fused heteroaromatic compounds with 5‐, 6‐ and 7‐membered rings, such as benzimidazole, quinoxaline and 1H‐1,5‐benzodiazepine derivatives, were synthesized through condensation reaction of o‐phenylenediamine with aryl aldehydes or ketones. The experimental conditions were carefully examined, and the products were characterized by 1H NMR, 13C NMR, MS, IR and elemental analyses. In addition, the structure of a benzodiazaepine derivative with 7‐membered ring was confirmed by single crystal X‐ray diffraction analysis.