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Novel Synthesis of 2-Alkylquinolizinium-1-olates and their 1,3-Dipolar Cycloaddition reactions with Acetylenes


Gebert, Andreas; Barth, Max; Linden, Anthony; Widmer, Ulrich; Heimgartner, Heinz (2012). Novel Synthesis of 2-Alkylquinolizinium-1-olates and their 1,3-Dipolar Cycloaddition reactions with Acetylenes. Helvetica Chimica Acta, 95(5):737-760.

Abstract

Several 2-alkylquinolizinium-1-olates 9, i.e., heterobetaines, were prepared from ketone 11, the latter being readily available either from pyridine-2-carbaldehyde via a Grignard reaction, followed by oxidation with MnO2, or from 2-picolinic acid (= pyridine-2-carboxylic acid) via the corresponding Weinreb amide and subsequent Grignard reaction. Mesoionic heterobetaines such as quinolizinium derivatives have the potential to undergo cycloaddition reactions with double and triple bonds, e.g., 1,3-dipolar cycloadditions or Diels-Alder reactions. We here report on the scope and limitations of cycloaddition reactions of 2-alkylquinolizinium-1-olates 9 with electron-poor acetylene derivatives. As main products of the reaction, 5-oxopyrrolo[2,1,5-de]quinolizines (= '[2.3.3]cyclazin-5-ones') 19 were formed via a regioselective [2+3] cycloaddition, and cyclohexadienone derivatives, formed via a Diels-Alder reaction, were obtained as side products. The structures of 2-benzylquinolizinium-1-olate (9a) and two '[2.3.3]cyclazin-5-ones' 19i and 19l were established by X-ray crystallography.

Several 2-alkylquinolizinium-1-olates 9, i.e., heterobetaines, were prepared from ketone 11, the latter being readily available either from pyridine-2-carbaldehyde via a Grignard reaction, followed by oxidation with MnO2, or from 2-picolinic acid (= pyridine-2-carboxylic acid) via the corresponding Weinreb amide and subsequent Grignard reaction. Mesoionic heterobetaines such as quinolizinium derivatives have the potential to undergo cycloaddition reactions with double and triple bonds, e.g., 1,3-dipolar cycloadditions or Diels-Alder reactions. We here report on the scope and limitations of cycloaddition reactions of 2-alkylquinolizinium-1-olates 9 with electron-poor acetylene derivatives. As main products of the reaction, 5-oxopyrrolo[2,1,5-de]quinolizines (= '[2.3.3]cyclazin-5-ones') 19 were formed via a regioselective [2+3] cycloaddition, and cyclohexadienone derivatives, formed via a Diels-Alder reaction, were obtained as side products. The structures of 2-benzylquinolizinium-1-olate (9a) and two '[2.3.3]cyclazin-5-ones' 19i and 19l were established by X-ray crystallography.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Chemistry
Dewey Decimal Classification:540 Chemistry
Language:English
Date:21 May 2012
Deposited On:22 May 2012 07:28
Last Modified:05 Apr 2016 15:49
Publisher:Verlag Helvetica Chimica Acta
ISSN:0018-019X
Funders:Swiss National Science Foundation, F. Hoffmann-La Roche AG
Publisher DOI:10.1002/hlca.201200038
Permanent URL: http://doi.org/10.5167/uzh-62448

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