An intramolecular iodine(III)-mediated keto-oximation of O-alkynyl hydroxylamines offers rapid and straightforward access to 3-acyl Δ2-isoxazolines and 1,2-oxazines. This approach features mild, metal-free, and aerobic reaction conditions with good functional group tolerance. Moreover, the synthetic utility of this method is demonstrated by the synthesis of unique structural motifs such as isoxazolidine, 3-vinyl isoxazoline, and 2,5-diphenylpyrazine derivatives by the conversion of 3-acyl Δ2-isoxazolines, thereby showcasing its efficiency and applicability in synthetic chemistry.