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Toward the Development of a Structurally Novel Class of Chiral Auxiliaries:  Diastereoselective Aldol Reactions of a (1R,2S)-Ephedrine-Based 3,4,5,6-Tetrahydro-2H-1,3,4-oxadiazin-2-one

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journal contribution
posted on 2002-09-17, 00:00 authored by David M. Casper, James R. Burgeson, Joel M. Esken, Gregory M. Ferrence, Shawn R. Hitchcock
Asymmetric aldol addition reactions have been conducted with (1R,2S)-ephedrine-derived 3,4,5,6-tetrahydro-2H-1,3,4-oxadiazin-2-one (2). Diastereoselectivities range from 75:25 to 99:1 for the formation of the crude non-Evans syn adducts 8ah. The facial selectivity of the enolate is directed by the stereogenic N4-methyl substituent. Aldol adduct 8a is readily cleaved by acid hydrolysis to afford (2S,3S)-3-hydroxy-2-methyl-3-phenylpropionic acid (9) in >95% ee.

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