Pyrrole undergoes electrophilic aromatic substitution more readily than benzene, and mild reagents and conditions are sufficient. These reactions normally occur at the 2-osition rather than the 3-position, as shown in the following example.

(a) Propose a mechanism for the acetylation of pyrrole just shown. You may begin with pyrrole and the acylium ion, CH3 - C ‰¡ O+. Be careful to draw all the resonance structures of the intermediate.
(b) Explain why pyrrole reacts more readily than benzene, and also why substitution occurs primarily at the 2-position rather than the 3-position.

Transcribed Image Text:

SnCl + CH3CO-C CH3 ,CH3 CH3-C-OH acetic anhydride H O pymole 2-acetylpyrrole