In connection with the abnormal reaction of ethyl 1-methyl-2-benzimidazolecarboxylate 3-oxide (1) with piperidine, aminolyses of several related esters were investigated. The esters: 1, 2-ethoxycarbonyl-1, 3-dimethylbenzimidazolium iodide (11), 2-methoxycarbonylmethyl- 1, 3-dimethylbenzimidazolium iodide (17), ethyl 2-benzothiazolecarboxylate 3-oxide (26) and 2-ethoxycarbonyl-3-methylbenzothiazolium perchlorate (34) under went abnormal aminolysis partly or predominantly, not only with secondary amine (piperidine) but also with some primary amines, to give the corresponding carbamates. Ethyl tribromoacetate (57) also underwent abnormal cleavage with some primary amines.
On the other hand, ethyl 1-methyl-2-benzimidazolecarboxylate (21), ethyl 2-benzothiazolecarboxylate (37), ethyl 2- and 4-pyridinecarboxylate N-oxide (44, 45) 4-ethoxycarbonyl- 1-methylpyridinium iodide (55) reacted with both primary and secondary amines to yield only normal products, amides.
Mechanisms accounting for the different behavior of the esters towards amines have been discussed from electronic and steric points of view.