Allylic oxidation and epoxidation of cycloalkenes by iodosylbenzene catalysed by iron(III) and manganese(III) tetra(dichlorophenyl)porphyrin: The marked influence of ring size on the rate of allylic oxidation

Five cis-cycloalkenes, with ring sizes 5, 6, 7, 8 and 10, and a cis-trans mixture of cyclododecene have been oxidised by iodosylbenzene using iron(III) or manganese(III) tetra(2,6-dichlorophenyl)porphyrin as catalysts, Both catalysts give very similar product distributions, although the reactions with the manganese porphyrin are sensitive to the presence of dioxygen whilst those with the iron porphyrin. are not. With all the substrates the dominant or sole reaction is epoxidation. However, with cyclopentene, cyclohexene and cyclododecene a significant amount of allylic oxidation also occurs. The dependence of the product distribution on the structure of the cycloalkene is discussed and attributed to the sensitivity of allylic oxidation rather than epoxidation to changes in ring size.