Selective ruthenium-catalyzed epimerization of chiral sec-alcohols

•Selective catalytic epimerization of readily available chiral secondary alcohols is demonstrated.•Rapid and inexpensive formation of the less abundant diastereomers is achieved under mild conditions.•Epicholesterol is produced by epimerization of cholesterol.

Extension of secondary alcohol racemization catalyzed by homogeneous half-sandwich ruthenium complexes to the epimerization of natural products containing additional non-functionalized stereo-centers has been investigated. Ruthenium-catalysed epimerization of the sec-alcohols (−)-menthol, (−)-isopulegol, (+)-borneol, (+)-fenchol and cholesterol under mild reaction conditions and low catalyst loadings (2 mol%) provides rapid access to their less abundant diastereoisomers (+)-neomenthol, (+)-neoisopulegol, isoborneol, beta-fenchol and epicholesterol in admixture with the parent diastereomers in ratios ranging from 1:4.9 to 1:2.4 (epimer:parent).

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