Chiral ( Z)-α,β-didehydroamino acid derivatives from a new chiral glycine equivalent with a 1,2,3,6-tetrahydropyrazin-2-one structure: applications to the synthesis of 1-aminocyclopropanecarboxylic acids and bicyclic α-amino acids

Abstract

The new chiral glycine equivalent 9, easily obtained from (+)-α-aminoisovalerophenone and glycine, afforded chiral ( Z)-α,β-didehydroamino acid (DDAA) derivatives 13 and 14 with a 1,2,3,6-tetrahydropyrazin-2-one structure. Compounds 13 and 14 were synthesised by reaction of 9 with Eschenmoser’s salt and by condensation reactions with aldehydes or acetone under PTC conditions, respectively. The diastereoselective cyclopropanation of 14, followed by hydrolysis, furnished (−)- allo-norcoronamic acid with high ee, whilst diastereoselective Diels–Alder reaction of dienophile 13 and cyclopentadiene afforded, after double bond hydrogenation and hydrolysis, (−)-2-aminonorbornane-2-carboxylic acid.