Stereospecific preparation of glycidic esters from 2-chloro-3-hydroxyesters. Application to the synthesis of (2R,3S)-3-phenylisoserine

Abstract

Abstract Cis - and trans -glycidic esters may be synthesized in high enantiomeric purities by cyclisation with potassium carbonate in DMF of the corresponding syn - or anti -2-chloro-3-hydroxyesters, prepared by microbial reduction of 2-chloro-3-oxoesters. In contrast, more basic media such as sodium ethylate afford exclusively the trans -isomer, whatever the stereochemistry of the starting 2-chloro-3-hydroxyester is. Cyclisation of deuterated compounds showed that this result was due to a rapid isomerisation of the syn esters into anti isomers before cyclisation. An application of this reaction to the synthesis of (2 R ,3 S )-3-phenylisoserinc is described.