Enantioselective Synthesis of anti-β-Substituted γ,δ-Unsaturated Amino Acids: A Highly Selective Asymmetric Thio-Claisen Rearrangement.

A novel synthesis of optically active anti-1β-substituted γ,δ-unsaturated amino acids via a thio-Claisen rearrangement has been achieved. A 2,5-diphenylpyrrolidine was used as a C2-symmetric chiral auxiliary to control the stereochemistry, giving good yields and excellent diastereoselectivities and enantioselectivities.