ELECTROGENERATED CHIRAL CATIONIC GLYCINE EQUIVALENTS - PART-2 - CHIRAL 3-METHOXY-2,5-MORPHOLINEDIONES FROM (S)-ALPHA-HYDROXY ACIDS AND DIMETHYL AMINOMALONATE

Chiral 3-methoxy-2,5-morpholinediones which are cyclic N,O-acetals hav e proved to be excellent chiral cationic amino acid equivalents, espec ially if larger nucleophiles are employed. They are easily obtained fr om dipeptolides formed between chiral alpha-hydroxy acids and dimethyl amino malonate via regioselective electrochemical methoxylation follo wed by intramolecular lactonization after decarboxylation. The lactoni zation can be performed quantitatively from the open-chain peptolide b y condenzation under reduced pressure at elevated temperature. The eas y separation of the desired amino acid and the alpha-hydroxy acid bein g the chiral auxiliary by extraction is valuable. (C) 1998 Elsevier Sc ience Ltd. All rights reserved.