Practical Synthesis of Natural Amino Acid Derivatives: Hf(OTf)4-Catalyzed Mannich-Type Reaction of Ketene Silyl Acetals or Enol Silyl Ethers with N,O-Acetals as a Glycine Cation Equivalent

The authors demonstrated the Hf(OTf)(4)-catalyzed Mannich-type reaction of an enol silyl ether and a ketene silyl acetal with an NO-acetal leading to the preparation of amino acid derivatives. In particular, use of the N,O-acetal having a bis(trimethylsilyl)amino group directly produced N-unprotected aspartic acid derivatives after a standard aqueous workup.