Palladium(II)-catalyzed oxidation of cyclopentene in the presence of copper(II) chloride and molecular oxygen

Abstract

The oxidation of cyclopentene to cyclopentanone with alcoholic palladium(II) salt has been investigated. PdCl 2 coupled with CuCl 2 or FeCl 3 as co-catalyst afforded cyclopentanone with high yield in alcoholic solvents at moderate temperatures. Under atmospheric pressure of oxygen, use of FeCl 3 as co-catalyst resulted in high selectivity to cyclopentanone, >90%, at ~50% cyclopentene conversion. An increase in oxygen pressure to 490.3 kPa favored the selective oxidation with PdCl 2-CuCl 2 catalyst, to afford the almost complete conversion of cyclopentene to cyclopentanone. The PdCl 2—CuCl 2 couple catalyzed the mono-oxygenation of cyclopentene to cyclopentanone with dioxygen, the reaction rate depending greatly on the oxygen pressure. These results cannot be accounted for by the conventional Wackertype catalysis; a hydroperoxopalladium(II) species coupled with Cu(II) is most likely the active species.