Investigation of UV Light-Promoted Synthesis of α‑Sulfonyl Amides from N‑Sulfonyl Ynamides

UV light-promoted synthesis of α-sulfonyl amides from N-sulfonyl ynamides without any additives is reported. The reaction proceeds through a radical chain mechanism involving the photoinduced cleavage of the nitrogen–sulfur bond and addition of an electrophilic sulfonyl radical to the triple bond of the ynamide followed by β-fragmentation of the sulfonyl group leading to a ketenimine hydrated upon workup. This highly efficient rearrangement leads, after acidic treatment, to a wide range of α-sulfonyl amides in high yields.