ASYMMETRIC-SYNTHESIS OF MALIC ACID-TYPE SYNTHONS VIA CHIRAL NOREPHEDRINE-DERIVED OXAZOLIDINES

Polyoxygenated C4 synthons 5-7 are synthesized in enantiomerically pure form starting from ephedrine derived oxazolidines 2,4 and 13. The 1,4-benzylate addition to 2 and 4, the key step in the synthesis of 5 and 6, proceeds cleanly with almost complete diastereoface selection. The key steps in the synthesis of target 7 are the nucleophilic epoxidation of aldehyde 13 and the lithium dimethyl cuprate epoxide opening, both of which proceed with high regio and stereocontrol. This route compares favorably with synthesis from malic acid, in that both enantiomers of ephedrine are available cheaply and it provides three differentiated oxygenated positions directly. © 1990.