OXIDATION OF IMINES TO OXAZIRIDINES CATALYZED BY TRANSITION-METAL COMPLEXES USING MOLECULAR-OXYGEN AS THE TERMINAL OXIDANT

The metal-catalysed oxidation of imines using molecular oxygen as the terminal oxidant and aldehydes as co-reductants has been studied. Diff erent transition metal complexes have been tested as catalysts and it is found that cobalt complexes can catalyse the selective oxidation of imines to oxaziridines. The cobalt-catalysed oxidation of imines to o xaziridines is dependent on the aldehyde used as co-reductant; thus, t he presence of aliphatic aldehydes leads to a smooth oxidation, whilst in the presence of aromatic aldehydes there was no reaction. The oxid ation proceeds well for imines with aliphatic and aromatic substituent s attached to the nitrogen and carbon atom, respectively. The electron ic nature of the oxygen atom transferred in these reactions, investiga ted using thianthrene 5-oxide as a probe, was found to be electrophili c in character. The mechanistic aspects of the cobalt-catalysed oxidat ion of imines to oxaziridines, probably involving a peroxyacyl cobalt intermediate, are discussed.