N -Arylethynylsulfonamides are oxidized into N -sulfonyl-2-aryloxoacetamides directly and efficiently with dimethyl sulfoxide (DMSO) as both an oxidant and solvent with microwave assistance. DFT calculations indicate that DMSO nucleophilically attacks the ethylic triple bond and transfers its oxygen atom to the triple bond to form zwitterionic anionic N -sulfonyliminiums to trigger the reaction. Then it nucleophilically attacks the generated iminium intermediates to accomplish the oxidation via the second oxygen atom transfer. The current method provides a straightforward and efficient strategy to transform various N -arylethynylsulfonamides into N -sulfonyl-2-aryloxoacetamides, sulfonyl oxoacetimides, without any other electrophilic activators or oxidants.