Lewis Acid-catalyzed Asymmetric Fluorinations of β-Keto Esters: Dramatic Improvement in Enantioselectivity by Changing the Operation Sequence

Efficient Lewis acid-catalyzed asymmetric fluorination and chlorination of β-keto esters were achieved using hybrid chiral oxazoline ligand 1. The enantioselectivity of the halogenated products dramatically increased when the reaction procedure was changed.