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Unravelling the reaction mechanism of the reductive ring contraction of 1,2-pyridazines

dc.contributor.authorSilva, Pedro J.
dc.date.accessioned2012-08-02T13:56:27Z
dc.date.available2012-08-02T13:56:27Z
dc.date.issued2012
dc.description.abstractSubstituted pyrroles may be synthesized from selected 1,2-pyridazines through a reductive ring contraction involving the addition of four electrons and four protons. Our density functional theory computations of this reaction mechanism show that the first reduction event must be preceded by the uptake of one proton by 1,2-pyridazine and that the reaction proceeds through a 2e–/3H+-bearing intermediate. In the absence of electron-withdrawing groups able to resonate charge away from the ring, this intermediate lies too high in energy, making the reaction sequence thermodynamically inaccessible. After another two-electron reduction and the addition of two more protons, the original 1,2-pyridazine ring opens. Ring contraction and ammonia elimination then proceed with very small barriers, irrespective of the substituents present in the original 1,2-pyridazine. By establishing the need for electron-withdrawing resonant groups in the 3- and 6-positions to stabilize the critical intermediate in the initial stages of the reaction, this work suggests that the scope of the reductive ring contraction of 1,2-pyridazines may be expanded to pyridazines bearing COCH3 groups, amides or aryls in these positions. We also explain the lack of reactivity of unsubstituted 1,2-pyridazine and analyze the feasibility of bypassing the high energy 2e–/3H+-intermediate through disproportionation of earlier 2e–/2H+-bearing intermediates.por
dc.identifier.citationSilva, Pedro J. (2012). Unravelling the Reaction Mechanism of the Reductive Ring Contraction of 1,2-Pyridazines. The Journal of Organic Chemistry, 77 (10), 4653-4659. DOI: 10.1021/jo300448d. ISSN 1520-6904.por
dc.identifier.issn1520-6904
dc.identifier.urihttp://hdl.handle.net/10284/3292
dc.language.isoengpor
dc.peerreviewedyespor
dc.publisherAmerican Chemical Societypor
dc.relation.publisherversionThe definitive version is available at: http://pubs.acs.org/doi/abs/10.1021/jo300448d/ A versão definitiva está disponível em: http://pubs.acs.org/doi/abs/10.1021/jo300448dpor
dc.titleUnravelling the reaction mechanism of the reductive ring contraction of 1,2-pyridazinespor
dc.typejournal article
dspace.entity.typePublication
oaire.citation.endPage4659por
oaire.citation.issue10
oaire.citation.startPage4653
oaire.citation.titleJournal of Organic Chemistrypor
oaire.citation.volume77
person.familyNameSilva
person.givenNamePedro
person.identifier.orcid0000-0001-9316-9275
person.identifier.scopus-author-id55310885700
rcaap.rightsopenAccesspor
rcaap.typearticlepor
relation.isAuthorOfPublicationf4a9230e-0a0e-45b6-b894-e71ded186ef2
relation.isAuthorOfPublication.latestForDiscoveryf4a9230e-0a0e-45b6-b894-e71ded186ef2

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