Pyrrole, Furan And Thiophene

Question 1

Reactivity towards EAS and why?

Answer 1

Pyrrole > furan > thiophene > benzene
More electronegative the heteroatom = more able to stabilise positive charge in intermediate

Question 2

Pyrrole EAS

Answer 2

Attack at C2 preferred = more resonance stabilisation

Question 3

Pyrrole/furan in strong acid

Answer 3

Unstable = polymerises

Question 4

Vilsmeiner Reagents

Answer 4

Pyrrole + DMF with 1. POCl3 2. Na2CO3, H2O gives aldehyde attached to pyrrrols C2

Question 5

Mannich reaction

Answer 5

Pyrrole with secondary amine, CH2O and acid catalyst gives secondary amine added to Pyrrole C2

Question 6

Reactivity of furan thiophene reactivity

Answer 6

Less reactive than Pyrrole so need LA catalyst for acylation

Question 7

Thiophene cycloadditions

Answer 7

Doesn’t undergo Diels-Alder as oxidation to sulfone destorys aromaticity

Question 8

Indole reactivity towards EAS

Answer 8

Sub at C3 as it doesn’t disrupt benzene aromaticity