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Molecules 2010, 15(3), 1722-1745; doi:10.3390/molecules15031722
Review

Reactivity and Synthetic Applications of 4,5-Dicyanopyridazine: An Overview

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Received: 28 December 2009 / Revised: 12 February 2010 / Accepted: 5 March 2010 / Published: 12 March 2010
(This article belongs to the Special Issue Advances in Heterocyclic Chemistry)
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Abstract

Despite the poor reputation of electron-deficient pyridazines in intermolecular Hetero Diels-Alder (HDA) reactions, 4,5-dicyanopyridazine (DCP) showed a surprising reactivity as a heterocyclic azadiene in inverse electron-demand HDA processes with different dienophiles. The use of alkenes, alkynes and enamines as 2p electron counterparts afforded dicyanocyclohexa-1,3-dienes and substituted phthalonitriles, respectively, while the use of suitable bis-dienophiles provides a general strategy for the one-pot synthesis of polycyclic carbo- and hetero-cage systemsthrough pericyclic three-step homodomino processes. HDA reactions with heterocyclic dienophiles allowed direct benzoannelation: in particular, pyrrole and indole derivatives were converted to dicyano-indoles and -carbazoles. In addition an unprecedented reactivity of DCP as a very reactive heterocyclic electrophile at the C-4 carbon was also evidenced: by changing the experimental conditions, cyanopyrrolyl- and cyanoindolyl-pyridazines were obtained through reactions of pyrrole and indole systems as carbon nucleophiles in formal SNAr2 processes where a CN group of DCP acts as leaving group. Thus, careful control of the reaction conditions allows exploitation of both pathways for the synthesis of different classes of heterocyclic derivatives.
Keywords: pyridazine derivatives; Hetero Diels-Alder reactions; nucleophilic aromatic substitutions; cage compounds; phthalonitriles pyridazine derivatives; Hetero Diels-Alder reactions; nucleophilic aromatic substitutions; cage compounds; phthalonitriles
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Alfini, R.; Cecchi, M.; Giomi, D. Reactivity and Synthetic Applications of 4,5-Dicyanopyridazine: An Overview. Molecules 2010, 15, 1722-1745.

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