α,β-Unsaturated Carboxylic Acid Derivatives. XIX. The Convenient Synthesis of α-Alkoxy-, α-Hydroxy-α-amino Acid, and Its Cyclic Dipeptide from α-Dehydroamino Acid
The facile conversion of α-dehydroamino acid into α-alkoxy-α-amino acid and its cyclic dipeptide is described. The reaction of t-butyl 2-acetylamino-2-alkenoate or 1-benzyl-3-ethylidene-2,5-piperazinedione with alcohol, water, or acetic acid in the presence of NBS or NGS, followed by reduction with 10% Pd–C, gives t-butyl 2-alkoxy-, 2-hydroxy-, and 2-acetoxy-2-(acetylamino)alkanoates, and 3-alkoxy-3-ethyl-2