AbstractAddition of phenyl‐, alkyl‐, alkenyl‐ and alkinyl‐Grignard reagents to pyridine‐N‐oxide in THF leads to 5‐substituted (2Z, 4E)‐pentadien‐aldoximes 6 having (E) (syn)‐configuration of the C, N‐double bond. The unsaturated oximes are shown to arise through an electrocyclic ring opening reaction from the primary Grignard adducts 5. These can be trapped by protonation at low temperature.