react with compounds 3 thus avoiding their isolation which is troublesome and yield lowering because imines are known to be rather instable compounds the method of the present invention is superior because of the simplicity of the procedure which does not require any isolation of the intermediates as well as of troublesome chromatographic purifications mild conditions are needed to deprotect both the hydroxy and the carboxy groups this is important because the risk of racemization is fully avoided good yields and diastereselection are a further essential advantage the present process affords a racemic mixture of isoserine derivatives which can be separated by conventional procedures however if desired the resolution step is easily avoided and enantiopure compounds are obtained directly if enantiopure protected glycidic acid 10 is used incl 3 was previously anhydrified at 200 u00b0 c under vacuum for 2 h 2 3 butandione 4 6 ml 46 22 mmol and glycolic acid 3 07 g 40 40 mmol were dissolved in ethyl orthoformate 40 ml and a catalytic amount of h 2 so 4 was added the reaction mixture was stand at 25 u00b0 c for 1 h a saturated solution of nahco 3 10 ml was added and the mixture was extracted with acoet 3 u00d7 30.