Isoxazolines are a class of five-membered heterocyclic chemical compounds, containing one atom each of oxygen and nitrogen which are located adjacent to one another.

The relatively weak N-O bond makes isoxazolines prone to ring-opening and rearrangement reactions.

A number of naturally occurring isoxazolines with possible anti-cancer activity are produced by marine sponges.

[6] 3-isoxazolines are prepared from 2-isoxazolines via their N-methylation to form 2-isoxazolinium salts, followed by nucleophilic attack and deprotonation.

[8] This can be considered an extension of the more common nitrone-olefin (3+2) cycloaddition used for creating isoxazolidines.