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THIOPHENES

THIOPHENES. Reactions with electrophiles at C Preferably at C-2 / C-5 (cf pyrroles). -Protonation Much more stable under acidic conditions than pyrroles and furans Protonation at C-2 /C-5. Reactions with electrophiles at C. -Nitration Not complete selectivity

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THIOPHENES

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  1. THIOPHENES Reactions with electrophiles at C Preferably at C-2 / C-5 (cf pyrroles) • -Protonation • Much more stable under acidic conditions than pyrroles and furans • Protonation at C-2 /C-5

  2. Reactions with electrophiles at C • -Nitration • Not complete selectivity • Not HNO3 (explotions)

  3. Reactions with electrophiles at C • -Halogenation • ca 108 times more reactive than PhH Chlorination Bromination Iodination

  4. Reactions with electrophiles at C • -Acylation • (FC alkylation not good react) (strong Lewis acid, AlCl3, polym.) • -Condensation with carbonyl comps c.f.

  5. Reactions with electrophiles at C • -Condensation with carbonyl comps, cont. • -Condensation with imines / iminium ions Mannich react. in case of pyrrol, Mannich reag. generated in situ Thiophene (and furan): Preformed reagent generally required

  6. Reactions with electrophiles at Sulfur • Possible for thiophene; S in 3rd row • Not possible for furan / pyrrole; O and N in 2nd row • Probably sp3 S. tetrahedral • Works best for electron rich thiophenes

  7. Reactions with electrophiles at Sulfur React. with carbenes

  8. Reactions with electrophiles at Sulfur React. with carbenes

  9. Reactions with electrophiles at Sulfur Reactions with nucleophiles NB! Electron rich Aryl

  10. Reactions with nucleophiles

  11. C-metallation and further reactions

  12. Pd cat. couplings Reat with radicals Seldom synthetically usefull Cycloadditions Easier with furan

  13. Oxythiophenes c.f. Aminothiophenes c.f. Aminopyrroles -Amino (not iminoform) - unstable

  14. Synthesis of Thiophenes Carbonyl condensations Strategy a

  15. Strategy a, cont. Strategy b Strategy c

  16. Strategy d Hinsberg synth.

  17. Miscellaneous carbonyl reactions

  18. Cycloadditions

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