In Clayden, Greeves, & Warren: Organic Chemistry Second Edition, it is said that indolizine (pyrrocoline) reacts in electrophilic aromatic substitution at the C3 of the pyrrole ring, as shown. enter image description here

I understand that it reacts at the pyrrole ring because the pyrrole ring is more nucleophilic than the pyridine-like ring, but I don't understand why it doesn't react at the C5 position of the pyrrole ring (like pyrrole does); the sigma complex at the C5 position has more extensive delocalization, whereas the sigma complex at C3 is less stable cross-conjugation.

  • $\begingroup$ Meh, it's not like things like that can be reliably explained like this, in general. $\endgroup$ – Mithoron Aug 19 '19 at 22:59
  • $\begingroup$ @Mithoron Then what would you say are the concepts which explain this? $\endgroup$ – Cyclopropane Aug 19 '19 at 23:33

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