Construction of Versatile N-Heterocycles from in situ Generated 1,2-Diaza-1,3-dienes

N-Heterocyclic architectures are omnipresent in many bioactive natural products, synthetic drugs, and materials science, thus have evoked a vast research interest of academic, as well as industrial chemists. Recently, several efficient methods have been developed for the preparation of various nitrogen-containing compounds with in situ generated 1,2-diaza-1,3-dienes from the easily available precursors including α -haloketohydrazones, α-hydroxyl ketohydrazones, thiadiazole dioxides or their analogues, and other simple hydrazones. These methods are considered powerful tools in the synthesis of five-, six- and seven-membered ring heterocyclic compounds with good to excellent levels of conversions and selectivities. This review mainly summarizes recent advances on the chemistry of construction of versatile N-heterocycles from in situ generated 1,2-diaza-1,3- dienes and presents an extensive summary of the application scopes and limitations of the corresponding cyclization reactions. Moreover, enantioselective approaches are also covered.