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2,3-Dihydro-1H-benzo[c]pyrazolo[1,2-a]cinnolines and derived radical cations

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Neugebauer,  Franz A.
Department of Organic Chemistry, Max Planck Institute for Medical Research, Max Planck Society;

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Fischer,  Hans
Department of Organic Chemistry, Max Planck Institute for Medical Research, Max Planck Society;

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Citation

Neugebauer, F. A., & Fischer, H. (1989). 2,3-Dihydro-1H-benzo[c]pyrazolo[1,2-a]cinnolines and derived radical cations. Journal of the Chemical Society-Perkin Transactions 2, (9), 1349-1353. doi:10.1039/P29890001349.


Cite as: https://hdl.handle.net/21.11116/0000-000A-B556-9
Abstract
A series of 2,3-dihydro-1H-benzo[c]pyrazolo[1,2-a]cinnolines (3a–f) has been prepared via alkylation of the benzo[c]cinnolines (1a–f) with 1,3-dibromopropane and subsequent reduction of the formed benzo[c]pyrazolo[1,2-a]cinnolinium bromides (2a–f) with sodium borohydride. The dark-red intermediate in the synthesis, reported to have a 2,3-dihydrobenzo[c]pyrazolo[1,2-a]cinnolinium structure (6a), is shown to be (2a) contaminated with some radical cation (3a)+·. The radical cations (3a–f)+·, readily generated in the oxidation of (3a–f), have been studied using e.s.r. and ENDOR spectroscopy. Relative signs of the 1H-coupling constants have been obtained by general triple resonance. This has led to full assignments in all cases.