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Synthesis 2009(23): 4049-4057  
DOI: 10.1055/s-0029-1217071
PAPER
© Georg Thieme Verlag Stuttgart ˙ New York

A New Route to Ring-Fused Pyrazines: Imidazo[4,5-b]Quinoxalines by a Simple Oxidation-Annulation Sequence

Svenja Herzoga, Gunther Buehrdela, Rainer Beckert*a, Susann Klimasa, Ernst-Ulrich Würthwein*b, Stefan Grimmeb, Helmar Görlsc
a Institute of Organic and Macromolecular Chemistry, Friedrich-Schiller-University Jena, Humboldtstr. 10, 07743 Jena, Germany
Fax: +49(3641)948212; e-Mail: C6bera@uni-jena.de;
b Organic-Chemistry Institute, University Münster, Corrensstr. 40, 48149 Münster, Germany
Fax: +49(251)8339772; e-Mail: wurthwe@uni-muenster.de;
c Institute of Inorganic and Analytical Chemistry, Friedrich-Schiller-University Jena, Lessingstr. 8, 07743 Jena, Germany
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Publication History

Received 25 June 2009
Publication Date:
22 October 2009 (online)

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Abstract

Novel tricyclic 4H-imidazo[4,5-b]quinoxalines were synthesized by a new ortho-annulation process starting from 4H-imidazoles and cerammonium nitrate (CAN) as oxidation reagent in the presence of potassium carbonate as base. This reaction is interpreted as a multi-step reaction involving oxidative radical formation, a radical aromatic substitution and a subsequent redox process. The analysis is supported by high level DFT calculations. This novel transformation opens the way for the construction of ring-fused derivatives of pyrazine. The new tricyclic products display strong fluorescence in solution and, in addition, show reversible redox activity.

Key words

amines - heterocycles - oxidations - radical reactions - ring-closure

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