Synthesis of β,γ‐Unsaturated D ‐α‐Amino Acids from L ‐Cysteine

D-α-Amino acids 2 are accessible in high optical purity by acid hydrolysis of the 5-thiazolidinone 1. Compounds of the type 1 can be prepared in a few reaction steps from L-cysteine; during the conversion of 1 into 2 unsaturated residues R remain intact. Boc = tert-butoxycarbonyl.