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 H₂O as a green oxygen source, this method provides an environmentally friendly route to α,α-dihaloketone derivatives.