Pyridines with leaving groups in position 3 do not give nucleophilic substitutions, but can undergo elimination in the presence of strong bases, leading to an intermediate called pyridine (equivalent to benzyne), which is attacked by the nucleophile in the middle.

pyridine 01


Stage 1. Formation of pyridine

pyridine 02

Stage 2. Nucleophilic attack

pyridine 03

Stage 3 . Protonation.

pyridine 04