Activation of Alkynes With an NXS/DMF System Employing Water as a Green Oxygen Source: An Efficient Route to α,α ‑Dihaloketones

We report an NXS/DMF‐mediated oxyhalogenation of alkynes that furnishes α,α ‐dihaloketones in moderate to excellent yields under mild, metal‐free conditions. The protocol is general for NCS, NBS, and NIS, delivering the corresponding dichloro‐, dibromo‐, and diiodo‐ketones, and it is applicable to internal alkynes with broad functional‐group tolerance. Mechanistic studies indicate activation of the alkyne by the NXS/DMF ensemble, in situ generation of halide species, nucleophilic addition of water, and deprotonation to give the products. Using NXS as a mild halogen source and H 2 O as a green oxygen source, this method provides an environmentally friendly route to α,α ‐dihaloketone derivatives.