Herstellung vonerythro‐2‐Hydroxybernsteinsäure‐Derivaten aus Äpfelsäureester. Vorläufige Mitteilung
Preparation for erythro ‐2‐Hydroxy‐succinic Acid Derivatives from Malic Esters As a contribution to the much discussed diastereoselective synthesis of enantiomers of open chain compounds, > 90% erythro ‐selective branching of malic esters by alkylation of the doubly deprotonated derivative 2 (alkoxide‐enolate) with methyl, allyl, and benzyl halides in THF at −78° (→ 3aa, 3ba, 3bb, 3bc , Table 1 ) is described. A second alkylation (→ 4 ) and addition of 2 to acetone (→ 5 ) are also possible. Cyclization of 2 to the enantiomerically pure trans ‐epoxides 6 is achieved by treatment with iodine. Cuprate opening of 6b furnishes the same product 3ba obtained from the methylation of 2b , establishing the configurational assignment.