Asymmetric synthesis of α-amino acids from α,β-(Z)-didehydroamino acid derivatives with 1,2,3,6-tetrahydropyrazin-2-one structure

Chiral (Z)-α,β-didehydroamino acid (DDAA) derivatives 14, 15 and 16 are obtained from a new chiral iminic cyclic glycine template with 1,2,3,6-tetrahydropyrazin-2-one structure 10 by condensation with carbonyl compounds, Eschenmoserʹs salt and Bredereckʹs reagent, respectively. The didehydroalanine derivative 15 and the enaminone 16 can give DDAA derivatives 14 using Heck olefination and vinylic nucleophilic substitution. These DDAA derivatives 14 and 15 undergo diastereoselective cyclopropanation, 1,3-dipolar and Diels–Alder cycloaddition reactions giving, after hydrolysis, the corresponding cyclic and bicyclic α-amino acids.