Efficient large scale stereoinversion of (R)-ethyl 3-hydroxybutyrate

A three step method for the large scale preparation of enantiomerically pure ethyl (S)-3-hydroxybutyrate is reported starting from the commercial biopolymer poly[(R)-hydroxybutyrate]. The key step depends on the ability to cleanly invert the stereochemistry of (R)-ethyl 3-hydroxybutyrate via its mesylate ester under neutral conditions, avoiding the competing elimination process. This has been achieved in good (75%) yield on >100 g scale by controlled addition of the mesylate to a stirred slurry of calcium carbonate in water at 80 degreesC. (C) 2003 Elsevier Ltd. All rights reserved.