STEREOSPECIFIC PREPARATION OF GLYCIDIC ESTERS FROM 2-CHLORO-3-HYDROXYESTERS - APPLICATION TO THE SYNTHESIS OF (2R,3S)-3-PHENYLISOSERINE

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 (2R,3S)-3-phenylisoserine is described.