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PYRIDINES

PYRIDINES. Synthesis of Pyridines. From 1,5-dicarbonyl and ammonia (c.f. chapt. 3). From 1,3-dicarbonyl and enamine (c.f. chapt. 3). From 2 equivs. 1,3-dicarbonyl , aldehyde and ammonia - Hantzsch Synthesis. Various syntheses from other heterocycles. PYRIDINES.

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PYRIDINES

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  1. PYRIDINES Synthesis of Pyridines From 1,5-dicarbonyl and ammonia (c.f. chapt. 3) From 1,3-dicarbonyl and enamine (c.f. chapt. 3) From 2 equivs. 1,3-dicarbonyl , aldehyde and ammonia - Hantzsch Synthesis Various syntheses from other heterocycles

  2. PYRIDINES • Reaction with electrophiles - react. on N: • Protonation • Nitration • Sulfonation • Amination • Halogenation • Alkylation • Acylation

  3. Reaction with electrophiles - react. on C: Electrophilic Aromatic Substitution Electron defficient / Poor nucleophiles Difficult Electrophiles may react at N } • Not: • FC alkylation • FC acylation • Nitration • Sulfonation • Halogenation React. in 3-pos.

  4. Nitration Bakke: [1,5]-sigmatropic rearrang.

  5. Sulfonation Possible intermediates Halogenation

  6. Reaction with Nucleophiles X=H, Substitution with “hydride” transfer Nu: NaNH2 - amination - Chichibabin reaction Nu: BuLi, PhLi etc - alkylation / arylation Nu: NaOH - “hydroxylation” - NB! High temp }Attack in the 2-pos (not 4-pos) • X=LG, Displacement of good leaving group X: Halogen (F>>Cl,>Br,>I), -OSO2R, -NO2, -OR Via Pyridyne

  7. Metallation and Reactions with Electrophiles

  8. Direct Reactions with Electrophiles: Additions, Substitutions Some examples (c.f. react. with ArLi)

  9. Pd-Catalyzed Coupling reactions a) On metallated pyridines b) On halopyridines Reactivity X=I>X=Br/OTf>X=Cl

  10. Radical Reactions a) Reactions with C-radicals: Minisci React. b) Generation of / Reaction on pyridylradicals

  11. Reductions Photochemistry

  12. Oxy-, Thio- and Aminopyridines Structure - Tautomerism

  13. Reactions on Pyridones - With Electrophiles

  14. Reactions on Pyridones - Deprotonation - O or N-substitution Reactions on Pyridones - Replacement of Oxygen

  15. Thiopyridones

  16. Aminopyridines

  17. Alkyl- and Vinylpyridines Quartenary Pyridinium Salts Add of: -hydrides -dithionite -organometallics -stab. carbanions etc. etc.

  18. Co-enz. NAD+ Hydride add. to NAD+, SubH2 oxidized Nicotine amide: Vit. B3 Adenine: Vit. B4

  19. Pyridine N-oxides More activated for electrophilic and nucleophilic attack

  20. Electrophilic Ar. subst Rearrangements

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