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Electrophilic Reaction on Nitrogen

Electrophilic Reaction on Nitrogen. R = H: pKa 5,23. pKa - 0.27. pKa 6.95. Electrophilic Reaction on Carbon: Electrophilic Aromatic Substitution. 6-membered rings - electron deficient -  reactivity. Both C and N may react 3/5 pos. most reactive C Diazines less reactive.

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Electrophilic Reaction on Nitrogen

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  1. Electrophilic Reaction on Nitrogen R = H: pKa 5,23 pKa - 0.27 pKa 6.95

  2. Electrophilic Reaction on Carbon: Electrophilic Aromatic Substitution 6-membered rings - electron deficient -  reactivity • Both C and N may react • 3/5 pos. most reactive C • Diazines less reactive Benzo ring most reactive Much slower react. than naphthalene

  3. 5-membered rings - electron rich - reactive i E-fil. Ar subst. React. in a-position generally preferred Selectivity not always good React.: Pyrrole > thiophene > furan

  4. Nucleophilic Reaction on Carbon: Nucleophilic Aromatic Substitution • SNAr • SN1: Via diazonuim salts and arylic cation • Benzyne • SRN1: Involves radicals • VNS: Vicarious nucl. Subst.

  5. 6-membered rings - electron deficient - reactive in Nu-fil. Ar subst. 2 / 4 Pos. reactive; electron def. C, neg. charge partly on N in intermed 3 / 5-Pos. much less reactive (benzenoid pos.) 5-membered rings - electron rich - not reactive in Nu-fil. Ar subst.

  6. Radical Reactions 6-membered rings Electron rich radical Electron deficient heterocycle 5-membered rings Electron rich heterocycle Electron def. radical

  7. Deprotonation NH C-metallation C-Litiation: a) Direct litiation (C-H C-Met) (“Metal-Hydrogen exchange”) b) Metal-Halogen exchange (C-X C-Met) C-Met a) Transmetallation (C-LiC-Met) (Met≠Li) b) Insertion (C-X C-Met-X)

  8. Direct Litiation • Reactivity / Acidity / Anion Stability • Other subst - Directed ortho metallation • R-Li: Alkyllithium and lithium amides

  9. Metal - Halogen Exchange R-Li: Alkyllithium, NOT LDA etc. Metall - halogen exchange favored over direct litiation, low temp. Formation of R-X may be avoided; 2 equivs. t-BuLi

  10. 5-Membered rings - examples

  11. 6-Membered rings

  12. Magnesium Derivatives Zinc Derivatives Boron / Silicon / Tin Derivatives Transmetallaton

  13. Reactions on Metallated Heterocycles Pd-Catalyzed coupling reactions (C-C bond): Zn, Sn, B Ipso Substitution (react with E+): Si, Sn

  14. Metallation in Alkyl Side Chains

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