Visible‐Light Mediated Metal‐free Synthesis of 3‐Bromo Coumarins Using In situ Generated Transient Non‐Symmetric Bromoiodanes

Abstract We report herein the in situ generated transient non‐symmetric bromoiodanes promoted regioselective intramolecular halocyclization of alkynoates for the first time under visible light irradiation enables the formation of 4‐aryl‐3‐bromocoumarin derivatives. Using this protocol, a broad range of valuable brominated coumarins can be synthesized in moderate to excellent yield using simple household CFL bulb as light source under photocatalyst free condition. In addition, preliminary control studies were conducted to gain more insights to propose the plausible reaction mechanism.