Recent Advances on the Synthesis of Nine-Membered N-Heterocycles

Nine-membered N-heterocycle scaffolds are widely found in natural products and biologically active molecules.The rigid structure of the medium-sized ring plays important roles in the regulation of their biological and pharmacological activities.Therefore, nine-membered N-heterocycle is one of the most attractive medium-sized ring compounds.Because of the increasing entropy and ring extension of nine-membered ring skeleton, the synthesis of nine-membered N-heterocycles is still difficult; especially the effective control of substituent stereoselectivity for the nine-membered ring is one of the greatest challenging topics This review summarizes the novel synthetic strategies of nine-membered N-heterocycles and their applications in the synthesis of natural products and pharmaceutically active molecules containing nine-membered ring scaffold in recent years.Keywords nine-membered N-