| abstract |
A process for preparing enantiopure E-(2S)-alkyl-5-halopent-4-enoic acids and their esters of the formula (I), in which R is a C1-C6-alkyl radical, R1 is H or C1-C4-alkyl and X is chlorine, bromine or iodine, in which the corresponding racemic 2-alkyl-5-halopent-4-enoic acid a) is reacted in a suitable solvent first with (S)-3-Methyl-2-phenylbutylamine, quinine or with N-methyl-D-glucamine, after which b) the corresponding (S)-3-Methyl-2-phenylbutylamine salt, quinine or glucamine salt of the (R)-pentenoic acid is precipitated and removed, and c) the remaining filtrate is mixed with a second chiral base or an inorganic salt, after which the corresponding salt of the (S)-pentenoic acid is precipitated and d) is then converted into the corresponding E-(2S)-alkyl-5-halo-4-pentenoic acid and subsequently where appropriate into the corresponding ester of the formula (I) in which R1 is C1-C4-alkyl. |