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

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