Utilize este identificador para referenciar este registo: http://hdl.handle.net/10284/3292
Título: Unravelling the Reaction Mechanism of the Reductive Ring Contraction of 1,2-Pyridazines
Autor: Silva, Pedro J.
Data: 2012
Editora: American Chemical Society
Citação: Journal of Organic Chemistry. ISSN 1520-6904. 77, 10 (2012) 4653–4659.
Relatório da Série N.º: Journal of Organic Chemistry;77, 10
Resumo: Substituted 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.
Peer review: yes
URI: http://hdl.handle.net/10284/3292
ISSN: 1520-6904
Versão do Editor: The 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/jo300448d
Aparece nas colecções:FCS - Artigos em Revistas Científicas Internacionais com Arbitragem Científica

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