For the preparation of 3, the well-known Fischer indole synthesis [8] starting from the symmetrical diethyl 4-oxopimelate was chosen. Direct indolisation with phenylhydrazine hydrochloride in acidic medium led to a mixture of diester 3, phenylhydrazone 4, and pyridazinone 5, whereas a two step procedure, taking advantage of the smooth formation of pyridazinone 5, [9] followed by treatment with saturated HCl/MeOH solution at reflux, proved to be efficient (73% ...