Benzimidazol‐Derivate und verwandte Heterocyclen V. Die Kondensation von o‐Phenylendiamin mit aliphatischen und alicyclischen β‐Ketoestern

The products of the condensation of o‐phenylenediamine with ethyl acetoacetate were re‐investigated. Depending on the reaction conditions, 2‐methylbenzimidazole (II), 2‐isopropenyl‐benzimidazole‐2‐one (VI) and 4,7‐dihydro‐5‐methyl‐1H‐2,3‐benzo‐1,4‐diazepin‐7‐one (IV) were obtained. 2‐Acetonylbenzimidazole, which had erroneously been described in the literature, could not be isolated from the above mentioned reaction; it was prepared by condensing o‐phenylenediamine with the ketal of ethyl acetoacetate followed by hydrolysis of the ketal group. The investigation was extended to the reaction of o‐phenylenediamine with 2‐carbethoxycyclohexanone and 2‐carbethoxycyclopentanone as well as with N‐substituted 3‐carbethoxy‐4‐piperidones.