Diastereoselective and Enantioselective Synthesis of α-p-Methoxyphenoxy-ß-Lactones: Dependence on the Stereoelectronic Properties of the ß-Hydroxy-α-p-Methoxyphenoxycarboxylic Acid Precursors.

Treatment of ß-hydroxy-α-p-methoxyphenoxy carboxylic acids derived from the asymmetric glycolate aldol addition reaction with p-nitrobenzenesulfonyl chloride yielded divergent results depending on the nature of the ß-substituent of the carboxylic acid. Substrates bearing either alkyl substituents (R = -n-butyl, -n-octyl, -benzyl, isopropyl, -tert-butyl) or aryl systems bearing electron-withdrawing substituents (R = -p-C6H4Cl, -p-C6H4Br, -p-C6H4NO2) yielded ß-lactones. In contrast, α-p-methoxyphenoxy-ß-hydroxycarboxylic acids bearing electron-donating aryl groups or the sterically demanding 2-naphthyl group formed (Z)-alkenes.