Oxidation of limonene catalyzed by MnIII(Salen)Cl-H2O

The cationic Mn^III(Salen) complex was proved to be an effective catalyst for the oxidation of limonene with iodosobenzene as terminal oxidant. For reactions conducted in CH₂Cl₂ at rt, with molar ratio of 1 0.05 1 (limonene: catalyst: iodosobenzene) limonene oxidation does occur with an optimal conversion of 60%. The major products according to HRGC-MS and HRGC-IR analyses were cis- and trans-l,2-epoxylimonene (30% and 16.7%, selectivity, respectively), the two diastereoisomers of 1p-menthen-9-al (20% selectivity), and carvone (10% selectivity). A turnover of 60 was observed at 1 0.01 1 ratio. The higher selectivity toward epoxide formation supports the rebound oxygen mechanism.