Oxonium ion-mediated synthesis of 4-substituted spiro-isoxazolines

The stereoselective synthesis of 4-bromo-spiro-isoxazolines was achieved in one step through the bromination of various isoxazoles that contain a pendant alcohol or carboxylic acid functional group. Isoxazole bromination leads to a bromonium ion intermediate, which opens either by neighboring oxygen lone pair electrons or by intramolecular nucleophilic attack. Single X-ray crystal data provide evidence that the two Contiguous stereocenters of the spiro-isoxazoline are formed by the anti intramolecular attack of the nucleophile relative to bromine, since there is air anti stereochemical relationship between the spirocyclic ring oxygen and the bromine atom. Published by Elsevier Ltd.