Rhodium- and Non-Metal-Catalyzed Approaches for the Conversion of Isoxazol-5-ones to 2,3-Dihydro‑6H‑1,3-oxazin-6-ones

Two approaches were developed for the conversion of isoxazol-5-ones to 2,3-dihydro-6H-1,3-oxazin-6-ones. The first involves dirhodium-catalyzed reaction of aryl diazoacetates, leading to rhodium carbene intermediates that undergo insertion into the N–O bond of isoxazol-5-ones. The second approach involves conversion of the aryldiazoacetates to the corresponding tosylates, followed by reaction with the isoxazol-5-one in a metal-free one-pot procedure. These studies illustrate an alternative method to achieve a carbene-like transformation without requiring a metal catalyst.