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Diazines: Reactivity and Applications in Organic Chemistry

Discover the unique reactivity of diazines, their reactions with electrophiles and nucleophiles, as well as their application in synthesis and medicinal chemistry. Diazines are versatile compounds that react differently than pyridines, offering new possibilities in chemical transformations. Learn about key reactions, including protonation, alkylation, and cycloadditions, and explore their significance in drug discovery and organic synthesis. This comprehensive guide covers various aspects of diazines, from basic reactivity to advanced applications in pharmaceuticals and bioactive compounds.

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Diazines: Reactivity and Applications in Organic Chemistry

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  1. DIAZINES Only C-5 in pyrimidine NOT elctron def. Diazines -Reacts even less readily with electrophiles than pyridine -Reacts easily with nucleophiles (additions / substitutions) -Reacts with nucleophilic radicals (Minisci) -Reacts as dienes in DA cycloadd. (less aromatic than pyridine)

  2. Reactions with electrophiles -Protonation -N-alkylation -Ox. to N-oxides (H2O2, peracids) -Pract. no E-fil Ar subst. (C-5 pyrimidine) -Halogenation by add. / elim. mechanisms c.f. pyridines weaker bases than pyridine

  3. Reactions with nucleophiles Addition - Rearomatization RMet: RLi, RMgX [ox]: DDQ, KMnO4 1,2- add 1,4-add Add. av NH2- (Chichibabin)

  4. Substitution on halodiazines Nucleophiles: -ammonia / amines -thiolates -malonates etc. -water / alchohols / alchoxides Leaving groups: -halogen -OMe -SO2Me rel. soft

  5. With hard Nu: Pd-cat. couplings

  6. Metallation

  7. Radical reactions (Minisci) Cycloadditions (DA)

  8. Oxydiazines Structure - Tautomerism React. with E-files More electron rich, reacts easier with E-files than diazines “OH” o/p directing

  9. React. with Nu-files Nu Ar subst More complex mech.:

  10. Undheim - Metaphase Inhibitors Metaphase Prophase Anaphase Telophase

  11. N-Deprotonation / Alkylation O-silylation / N-alkylation

  12. N-Deprotonation / Alkylation N-alkylation / C-alkylation N-alkylation / O-alkylation

  13. C-Deprotonation / Metallation Excess base Because of NH

  14. Replacement of oxygen Halogenation Oxo  thio

  15. Cycloadditions Cancer Psoralenes - Psoriasis

  16. Aminodiazines • Exists as aminodiazines (not imino…) • -NR2 electron donor: Stronger bases • -NR2 electron donor: Participates easier in E-fil Ar subst. • Diazotation reactions • Dimroth rearrangement Dimroth

  17. Synthesis of Pyridazines Carbonyl condensations Cycloadditions

  18. Synthesis of Pyrimidines Carbonyl condensations etc. Cycloadditions

  19. Bioactive Pyrimidines DNA bases Base pairs Double a-helix

  20. Anticancer comp. Antivirals HIV (RT -inhibitors) Barbiturates (old sedatives)

  21. Synthesis of Pyrazines Carbonyl condensations etc. Bioactive Pyrazines/Pyridazines: Pteridines Bacteria synthezize folic acid

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