Recycling Catalyst via Formation of Charge Transfer Complexes

Significance

The use of bis(oxazoline)-type catalysts as recyclable, charge-transfer complexes is a key feature of this report. The authors have nicely attached the bis(oxazoline)-type ligand to an electron-rich anthracene moiety that forms a complex with the electron-deficient trinitrofluorenone. This reusable catalyst was then shown to be effective for the asymmetric Diels-Alder reaction. After the reaction, the complex is precipitated by the addition of pentane and the products removed from the solid showing high enantioselectivity (up to 94%). The catalyst showed retention of reactivity through ˜10 runs.