Oxidation of cyclopentane-1,2-dione: a study with 18O labeled reagents

The asymmetric oxidation of 3-alkyl-cyclopentane-1,2-diones with the Ti(OiPr)4/tartaric ester/t-BuOOH complex, which gives, in a cascade process, highly enantiomerically enriched γ-lactone acids, was studied by 18O isotopic labeling in the substrate and in the oxidant. The path of the labeled atoms was followed by 13C NMR spectroscopy. It was found that the oxidative ring cleavage of 1,2-dione proceeds via a Baeyer-Villiger-type oxidation mechanism.