Copper Induced Cyclization of α,β-Unsaturated Carbonyl Compounds to Isoxazoles

An unusual synthesis of isoxazoles from α,β-unsaturated ketoximes is reported. Using very inexpensive reagents, isoxazoles are isolated in good yields. Notably, a mixture of E and Z oxime isomers is employed. Initial studies indicate the oxidative cyclization reaction does not proceed via radical route; a copper insertion/elimation route is proposed.