Preparation and characteristic odour of optically active 3-hydroxy-2-octanone

The preparation of optically active 3-hydroxy-2-octanone was examined by Sharpless asymmetric dihydroxylation of a silyl enol ether derived from 2-octanone. (R)-3-Hydroxy-2-octanone was obtained in 68% yield and 87.8% ee when AD-mix-β was used as an oxidant, while the (S)-enantiomer was produced in 69% yield and 77.3% ee from AD-mix-α. The characteristic odour of the optically active products was evaluated by chiral gas chromatography–olfactometry. (R)-3-Hydroxy-2-octanone has a mushroom-like, fresh grass odour, while the (S)-enantiomer presents a mushroom-like, earthy note. Aroma extract dilution analysis was applied to determine the flavour dilution factors of the two enantiomers. The flavour dilution factor of the (R)-enantiomer was 1024, which is much higher than that of (S)-enantiomer (256). They obviously differ in odour intensity. Copyright © 2012 John Wiley & Sons, Ltd.