Recent advances in transition metal-free annulation toward heterocycle diversity based on the C–N bond cleavage of enaminone platform

Enaminones and analogous stable enamines are well known as platform building blocks in organic synthesis for the construction of heterocyclic compounds, especially N-heterocycles. To date, enaminones have been successfully employed in the synthesis of various 5- or 6- membered heterocycles. Recently, synthetic protocols accomplished by diversity-oriented annulation reactions based on the C-N bond cleavage of enamines have gained notable success. In this review, the development of the transition metal-free heterocyclic product synthesis based on the annulation reactions of enaminones or analogous enamines featuring a C-N bond cleavage is reviewed.