Reaction products and mechanism of the regioselective oxidation of N-phenylmorpholine by ozone

The regioselective oxidation of N-phenylmorpholine by ozone in dichloromethane or acetonitrile produced a lactam and a diformylderivative. These products derive from the selective attack of ozone at the heterocyclic ring in one of the two non-equivalent reactive carbons. The reaction mechanism has been investigated by DFT calculations, which show that the reaction occurs through the insertion of ozone at the carbon-hydrogen bond of a methylene group of the morpholine ring. The regioselectivity is due to the significantly lower energy barrier calculated for the attack of ozone α to nitrogen than α to oxygen. In addition, the energy barrier decreases with increasing the polarity of the solvent, explaining the higher conversions observed for the reaction carried out in acetonitrile than in dichloromethane.