Einfache Umwandlung von (-)-(R)-3-Hydroxybuttersaeure in das (+)-(S)-Enantiomere und dessen Lacton (-)-(S)-4-Methyloxethan-2-on

Article abstract of DOI:10.1002/hlca.19870700513

Condensation of (R)-3-hydroxybutanoic acid (1) with ethyl orthoacetate gives a 2-ethoxy-substituted 1,3-dioxanone 2 which is thermally labile: at ca. 100 deg C, two competing processes commence, one leading to ethyl (R)-3-acetoxybutanoate (3), the other one - with complete inversion of configuration - to the (S)-4-methyloxetan-2-one (4) and ethyl acetate.These can be readily separated by fractional distillation.Thus, enantiomerically pure (S)-3-hydroxybutanoic acid (ent-1) and l-2-alkyl-3-hydroxybutanoic acid derivatives (such as 6 and 8) become available from the biopolymer PHB, the precursor to the acid 1.