Chapter 19, Problem 19.54SP

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

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