A Convenient Synthetic Approach to Phenazone Derivatives Containing a 1,2,4-Triazine or Pyridine Fragment

An efficient synthetic approach to phenazone derivatives containing a 1,2,4-triazine or pyridine fragment has been proposed on the basis of successive nucleophilic substitution of hydrogen ( $${\rm{S_N^H}}$$ ) in 1,2,4-triazine 4-oxides and aza-Diels-Alder reaction with norbornadiene as dienophile.