Transition-Metal-Free Synthesis of Substituted Pyridines via Ring Expansion of 2‑Allyl‑2<i>H-</i>azirines

A new strategy to open the 2-allyl-2<i>H</i>-azirines by 1,8-diazabicyclo[5.4.0]­undec-7-ene (DBU) promotion in metal-free conditions affording 1-azatrienes that <i>in situ</i> electrocyclize to the pyridines in good to excellent yields is reported. The reaction displays a broad substrate scope and good tolerance to a variety of substituents including aryl, alkyl, and heterocyclic groups. In addition, one-pot synthesis of pyridines from oximes via <i>in situ</i> formation of 2<i>H</i>-azirines was achieved