Reactions with electrophiles at C

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Presentation transcript:

Reactions with electrophiles at C 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 Not HNO3 (explotions)

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

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

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

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

Reactions with electrophiles at Sulfur React. with carbenes

Reactions with electrophiles at Sulfur React. with carbenes

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

Reactions with nucleophiles

C-metallation and further reactions

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

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

Synthesis of Thiophenes Carbonyl condensations Strategy a

Strategy a, cont. Strategy b Strategy c

Strategy d Hinsberg synth.

Miscellaneous carbonyl reactions

Cycloadditions