ERYTHRO-SELECTIVE ALDOL CONDENSATION USING DIRECTLY GENERATED TI-ENOLATES - APPLICATION TO THE SYNTHESIS OF PURE (1R,2S)-CHLORAMPHENICOL BASE AND (2R,3R) ALLO-THREONINE

The directly generated ((EtO)(3)TiCl/NEt(3), 0 degrees C or rt) titani um enolate of the ethyl iminoglycinate derived from (1R,2R,5R)-hydroxy pinanone undergoes erythro- and enantio-selective aldol condensations. Pure (1R,2S)-chloramphenicol base and pure D-allo-threonine were thus obtained in 5 steps and, respectively, 40% and 71% overall yields. Us ing X-ray diffraction analysis, the structure of the starting imino es ter and of the imino ester derived from threonine after aldolisation h ave been shown to be respectively E and E-2R,3R.