Transition-Metal-Free Synthesis of Pyridine Derivatives by Thermal Cyclization of N-Propargyl Enamines

Abstract

A transition-metal-free synthesis of pyridine derivatives by 6-endo-dig cyclization of N-propargyl enamines was developed. This method is environmentally friendly and is a high atom economy reaction that is easily accessed to provide pyridine derivatives in moderate to good yield by heating N-propargyl enamines in solvent without additives. The total synthesis of onychine was achieved in 51% yield in only two steps by using this method.