Gold-catalyzed Cyclization of Non-conjugated Ynone-oxime Derivatives: Incorporation of Solvent Molecule

Au-iii-promoted cyclization reaction of ynone-oxime derivatives furnished 4H-1,2-oxazine ring under mild reaction conditions. When an alcohol is present in the reaction media, it was attached to the oxazine ring by the second activation of cyclic intermediate with a gold catalyst. Cholesterol, propargyl alcohol, phenol, and some of the different alcohol derivatives with alkyl chain were bonded to the oxazine ring in good yields. While amine derivatives did not attach to the ring under optimized reaction conditions, the molecule with the thiol group deactivated the gold catalyst under the same reaction conditions and did not give any cyclic products. With the obtained cyclization protocol, 11 unknown oxazine derivatives were synthesized and characterized. The proposed cyclization mechanism was drawn according to the two independent control experiments, DFT optimization, and NBO charges.