L-Proline, 3-ethyl-, methyl ester, cis- (9CI) synthesis

Yield:-

Steps:

Multi-step reaction with 5 steps
1.1: LDA; zinc bromide / tetrahydrofuran / -78 - 20 °C
1.2: 74 percent / CuCN*2LiCl / tetrahydrofuran
2.1: 80 percent / mCpBA; TFA / CH₂Cl₂ / 1 h / 0 °C
3.1: 92 percent / LDA; DMPU / tetrahydrofuran / -78 °C
4.1: 84 percent / KH₂PO₄; Na/Hg amalgam / methanol / 1 h / 20 °C
5.1: H₂ / Pd/C / methanol

References:

Karoyan, Philippe;Chassaing, Gérard [Tetrahedron Letters,2002,vol. 43,# 7,p. 1221 - 1223]