Gernot A. Eller,1* Qian Zhang,1,2 Daniela Habicht,1 Barbara Datterl1 and Wolfgang Holzer1*
1 Department of Drug and Natural Product Synthesis, Faculty of Life Sciences,
University of Vienna, A-1090 Vienna, Austria
2 Department of Medicinal Chemistry, School of Pharmacy, Fudan University,
200032 Shanghai, PR China
* Corresponding author: E-mail: gernot.eller@univie.ac.at; wolfgang.holzer@univie.ac.at
Abstract
Derivatives of a novel tricyclic ring system,
pyrazolo[4’,3’:5,6]pyrano[2,3-b]pyrazin-4(1H)-one, were prepared by reaction
of either 1-substituted or 1,3-disubstituted 2-pyrazolin-5-ones and
3-chloro-2-pyrazinecarbonyl chloride in the presence
of Ca(OH)2 in refluxing 1,4-dioxane. In some cases the corresponding title
compounds thus were obtained directly
due to a spontaneous intramolecular nucleophilic substitution reaction of the
intermediate 4-pyrazinoylpyrazol-5-ols. In other cases mixtures of the latter intermediates and the target
compounds were obtained, which were completely
converted into the desired tricycles upon treatment with HCl in a
chloroform/methanol mixture. The parent system carrying
no substituent in positions 1 and 3 was prepared by treatment of the 1-PMB
(p-methoxybenzyl) protected congener
with trifluoroacetic acid. Detailed NMR spectroscopic data (1H, 13C,
15N) are
presented for the title compounds.
Keywords: Pyrazolones, cyclizations, NMR spectroscopy, fused heterocyclic systems.