N-acylaminophenylcyclopropanes in reaction with nitrous acid generated in situ

The reaction of N-acylaminophenylcyclopropanes with HNO₂ proceeds regioselectively with introduction of an N = O fragment into the three-membered ring and formation of the corresponding Δ²-isoxazolines. For ortho-substituted N-acylaminophenylcyclopropanes side processes were observed, caused by the intramolecular participation of the N-acyl group in conversions of the carbenium ions formed on opening the cyclopropane ring under the action of the nitrosating reagent, and by direct insertion of the modified ortho substituent into the three-membered ring.