An Improved Asymmetric Synthesis of Unusual Amino Acid (2S,3S)‐3‐Hydroxyproline

Abstract An improved three‐steps method for the conversion of N‐benzyl (S)‐3‐hydroxypyrrolidin‐2‐one 6 to (2S,3S)‐3‐hydroxyproline 1 is reported. The key step is the reductive cyanation of 6. The synthesis of 1 constitutes a formal asymmetric synthesis of (2S,3S)‐3‐hydroxyproline betaines 2. Keywords: 3‐Hydroxyproline3‐Hydroxyproline betainesReductive cyanation Acknowledgment We are grateful to the NNSC for financial support.