Synthesis of Isoxazoline Derivatives through Boulton-Katritzky Rearrangement of 1,2,4-Oxadiazoles

The base‐induced rearrangement of 1,2,4‐oxadiazoles into isoxazoline derivatives is reported. This represents the first example of a three‐atom side‐chain rearrangement that involves a saturated CCO side chain at C‐3 of the oxadiazole. Nonaromatic 3‐amino‐isoxazoline derivatives are obtained in good yields. Interestingly, this reaction occurs through the rearrangement of aromatic oxadiazoles to form less stable bonds than those that are broken. The first example of a Boulton‐Katritzky Rearrangement that involves an oxadiazole ring with a saturated CCO side chain is reported. From a mechanistic point of view, the results present a new and interesting feature of this reaction. Because of the presence of a stable intermediate, this rearrangement affords nonaromatic isoxazolines.