Preparation of optically pure enatiomers of Corey lactone by resolution of the racemate

Abstract

Racemic hydrogen butanedioates (IIa, IIb) and hydrogen pentanedioates (IIIa, IIIb), prepared by reaction of racemic Corey alcohols Ia, Ib with the corresponding acid anhydride, were resolved by optically active bases [(1R,2S)-(-)-ephedrine, (S)-(-)-1-phenylethylemine, quinine] to give the optically pure diastereoisomeric salts from which the individual enantiomers of hydrogen butanedioate IIa and IIb and hydrogen pentanedioate IIIa and IIIb were liberated. Acid-catalyzed transesterification with methanol converted these optically pure enantiomers into pure(-)-enantiomer Ia and (+)-enantiomer Ib of the Corey lactone.