Proline as Lewis base catalyst:: Diastereoselective synthesis of isoxazoline-N-oxide through [3+2] cycloaddition

A catalytic cascade synthesis of isoxazoline-N-oxide was developed through proline-catalyzed nitroalkene activation. A large substrate scope was obtained with good to excellent yields. Mechanistic studies revealed intramolecular cyclization as the rate-determining step, giving only trans isomers in all cases.