Pseudocyclic benziodoxole triflate as an effective reagent for the catalytic oxidative cycloadditions of aldoximes with nitriles and maleimides

Abstract

A novel hypervalent iodine(III) compound - pseudocyclic benziodoxole triflate (IBAOTf) - was prepared, isolated, identified and tested for its reactivity over various reactions in our previous research. Based on these preliminary results, we investigated the catalytic activity of the in situ generated IBA-OTf in cycloaddition reactions of numerous aldoximes with acetonitrile and maleimide to form 1,2,4-oxadiazoles and pyrrolo-isoxazoles, respectively. The presence of the in situ IBA-OTf species was confirmed by HR-ESI-MS and 1H NMR studies. By the reaction with IBA-OTf, the starting aldoximes were converted into the corresponding unstable nitrile oxides which were the active species reacting with acetonitrile or maleimide to form the corresponding heterocyclic five-membered ring products. Totally, nineteen 1,2,4-oxadiazoles and thirteen pyrrolo-isoxazoles have been successfully synthesized and their structures were authenticated by 1H and 13C NMR. X-ray single crystal diffraction was also performed for a typical pyrrolo-isoxazole to confirm the bicyclic structure of the products.