A Concise Route to Pyridines from Hydrazides by Metal Carbene N-H Insertion, 1,2,4-Triazine Formation, and Diels-Alder Reaction

simple, new three-step sequence for the conversion of hydrazides into pyridines is reported in which the key steps are N-H insertion by a copper carbene intermediate derived from alpha-diazo-beta-ketoesters into the hydrazide, reaction with ammonium acetate to give 1,2,4-triazines, followed by Diels-Alder reaction with norbornadlene.