Onium ions. X. Structural study of acyclic and cyclic halonium ions by carbon-13 nuclear magnetic resonance spectroscopy. Question of intra- and intermolecular equilibration of halonium ions with haloalkylcarbenium ions
An Efficient Chemoenzymatic Approach to (S)-γ-Fluoroleucine Ethyl Ester
摘要:
An asymmetric synthesis of (S)-gamma-fluoroleucine ethyl ester 1 is described. The key transformation involves a lipase-catalyzed dynamic ring-opening of 2-(3-butenyl)azlactone 7b with EtOH to give amide ester (S)-6b in 84% enantiomeric excess. Removal of the N-pentenoyl group with N,N-dibromodimethylhydantoin in the presence of trifluoroacetic acid afforded the titled compound, which was isolated as its hydrogen sulfate salt in 75% yield and > 97% ee.