Chapter 5. Heterocycles

Table of Contents
Pyridin
Pyron

Pyridin

Hantzsch

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Table 5-1. Hantzsch synthesis of pyridin

Molecular structuresReaction description
1,3-Dicarbonyl (e.g. beta-ketoester)if no other reagents are used and we work in a basic medium, we will obtain alpha-pyrone by condensation (the Section called Pechmann synthesis of Aplha-Pyron)

    • +NH3

    • +HCHO/Base

    • +Formaldehyd

    • imin formation (Retro Step: r1a)

    • The imin will be formated only on the reactive keto group, because the carbonyl-carbon atom of the ester is less electrophil caused by the +M effect of the alkoxy group.

  • imin-enamin-tautomerism, the enamin is more stable, because the formated conjugated system.

  • Attack of the enamin under michael-addition (the Section called Michael-Addition in Chapter 7)

  • nucleophilic attack to vinyl-like carbon-carbon double bond (Retro Step: r2)

 

  • enamin formation

  • keto-enol tautomerism

  • 6-exo-trig ring closure (Retro Step: r3)

  • imin-enamin tautomerism

1,4-Dihydropyridin

  • oxidation

  • HNO3 or DDQ

 

Breitmeier

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Guareshi-Thorpe

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Kroehnke

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Hetero-Diels-Alder

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Boennemann-Cycle

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Pyrrol and Dichlorcarben (weak basic medium)

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