Enantioselective synthesis of anti-beta-substituted gamma,delta-unsaturated amino acids: a highly selective asymmetric thio-Claisen rearrangement.

A novel synthesis of optically active anti-beta-substituted gamma,delta-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.