Visible-Light Catalyzed Desulfurative Cyclization for Synthesis of 3-Amino-[1,2,4]-triazolo Pyridine.

In this study, we developed a visible light-mediated catalytic system to facilitate the cyclization-desulfurization reaction between 2-hydrazinopyridine and isothiocyanate, enabling the direct synthesis of 3-amino-[1,2,4]-triazolopyridine derivatives through a one-pot method. This protocol allows for the efficient preparation of target products under mild and environmentally friendly conditions utilizing visible light irradiation and demonstrates good compatibility with various functional groups at room temperature. The gram-scale experiment further verified the potential of this method for industrial applications. Furthermore, the reaction process was systematically investigated by electron paramagnetic resonance (EPR) spectroscopy and the reactive oxygen species involved in the reaction were identified. On this basis, a rational reaction mechanism was proposed. This synthetic strategy aligns with the principles of green chemistry, providing a novel and efficient pathway for the construction of triazolopyridine skeletons.