Unexpected results in the heterocyclization of 5-acetylenylpyrazole-4-carboxylic acid hydrazides under the influence of CuCl: formation of a diazepinone and dehydrodimerization into the corresponding bis(pyrazolo[4,3-d][1,2]diazepinone)

The simple reaction of cyclization of hydrazides of vic-acetylenylbenzoic and acetylenylpyrazole carboxylic acid can lead to four different compounds: five-membered N-aminolactams, six-membered N-aminolactams, six-membered diazinones and diazepinones, but only the first three have been described. In this paper we report the unexpected formation of a bis(pyrazolo[4,3-d][1,2]diazepinone, the structure of which has been established by X-ray crystallography.