An easy route to enantiomerically pure 7- and 8-HSA by an olefin metathesis-based approach

Synthesis of enantiomerically pure 7- and 8-hydroxystearic acids1 (7- and 8-HSA) has been accomplished starting from chiral non racemic 1-pentadecen-4-ol 1a and 1- tetradecen-4-ol 1b respectively, in accordance with the retrosynthetic procedure depicted in the Scheme. Access to enantiomerically pure homoallylic alcohols 1a,b was possible via kinetic resolution of the corresponding racemic acetates, catalyzed by Novozym 435 (Lipase B from Candida antarctica). Yamaguchi esterification2 of 1a,b with 4-pentenoic and 5-hexenoic acids 2a,b respectively afforded the suitable dienic esters 3a,b which were submitted to Ring- Closing Metathesis Reaction (RCM).3 Hydrogenation of the resulting complex reaction mixtures followed by hydrolysis under basic conditions afforded the expected chiral non racemic 7- and 8-HSA in about 40% total yield. Scheme