Oxidative Halogenation of Alkenes or Alkynes via Visible Light Induces Singlet Oxygen Production

We report a mild visible light-promoted 1,2-difunctionalization of alkenes or alkynes for the synthesis of α-haloketones. The reaction employs O₂ as the green oxygen source and economically accessible NaBr and MgCl₂·6H₂O as the halogen source. In the mechanism, blue light excitation of the acetonitrile-oxygen complex generates singlet oxygen, which subsequently is converted into the superoxide ion. The halide ion then produces a halogen radical via electron transfer to the arene, thereby initiating the reaction to yield the product.