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. Keywords: Isoxazole, cyclization, copper-mediated, antiinflammatory, pharmaceuticals, antibiotic, ketoxime, anhydrous, Beckmann rearrangement, olefin-tethered substrate