Cu‐Catalyzed Synthesis of Isoxazolidine/1,2‐Oxazinane‐3‐ylidene Sulfonamide from O‐Alkynyl Hydroxylamines: A Route to Sulfamethoxazole Analogues

Cu‐catalyzed cascade [3+2] azide‐alkyne cycloaddition (CuAAC)/ketenimine/hydroamination reaction of alkynyl hydroxylamines that enables the rapid synthesis of isoxazolidine/1,2‐oxazinane‐3‐ylidene sulfonamides. Notably, this study presents the first examples of 1,2‐oxazinane‐3‐ylidene sulfonamide. The synthetic utility of this transformation is highlighted by the direct conversion of isoxazolidine‐3‐ylidine sulfonamides into 3‐amino isoxazolines and isoxazole derivatives. This strategy was used as a key step in the total synthesis of antibiotic sulfamethoxazole and its analogues.