Organic Halogenation using Inorganic Halides and Visible-Light Photocatalyst Perylenediimide

Halogenation reactions are fundamental in organic synthesis. While halogenation with fragile N-X (nitrogen-halogen) bonds is well-known in the literature, metal halide salts often require electrolysis. In this study, we unveil a novel and efficient visible-light-driven technique to utilize cheap metal salts, more specifically alkali metal salts, as an effective halogen precursor for the generation of halogen radicals using perylene bisimide (PDI) as a photocatalyst and N-fluorobenzenesulfonimide (NFSI) as the stoichiometric oxidant. To demonstrate the applicability further, the generated halogen radicals were scavenged in the alkyne systems to synthesize a library of α,α-dihaloketones in a polar solvent, overcoming challenges associated with the poor solubility of inorganic salts in organic media. Beyond alkali metal salts, this radical-mediated strategy is compatible with numerous other inexpensive halogenated salts, including those derived from transition metals, lanthanides, organohalogens, or organic amine-based salts with varying reaction yields. This synthetic protocol offers a sustainable and cost-effective alternative to conventional halogenation techniques, paving the way for broader applications in green and scalable synthetic methodologies.