Enantioselective Catalytic Synthesis of α-Halogenated α-Aryl-β-amino Acid Derivatives.

The enantioselective synthesis of a broad variety of novel differently functionalized α-halogenated α-aryl-β-amino acid derivatives by means of an ammonium-salt-catalyzed asymmetric α-halogenation of isoxazolidin-5-ones was accomplished. Key to success to obtain high levels of enantioselectivities was the use of Maruoka's spirocyclic binaphthyl-based ammonium salts, and detailed accompanying mechanistic studies using density functional theory methods revealed the key features for the catalyst-substrate interactions.