Chiral compounds of essential oils XIX. 4‐methyl‐5‐decanolide: Chirospecific analysis, structure and properties of the stereoisomers

Racemic mixtures of synthetic cis‐ or trans‐4‐methyl‐5‐decanolide were separated by enantioselective high performance liquid chromatography with Chiraspher‐RT to yield all four stereoisomers as enantiopure compounds of distinct odour activities. In order to elucidate stereochemical features the isolated stereoisomers were reduced to their corresponding 4‐methyl‐1,5‐decandiols by reductive ester cleavage with lithium aluminium hydride. Absolute configurations were derived from proton nuclear magnetic resonance studies of diastereomeric di‐(R)‐2′‐methoxy‐2′‐trifluoromethylphenylacetic acid esters of these 1,5‐diols. Using enantioselective multidimensional capillary gas chromatography (column combination SE 52/heptakis‐(2,3‐di‐O‐methyl‐6‐O‐tert butyldimethylsilyl)‐β‐cyclodextrin), the direct enantioselective analysis of all four lactone stereoisomers was achieved. The application of this method to the scent of living, white flowering orchids (Aerangis confusa) proves cis‐(4S)‐methyl‐(5S)‐decanolide as the unique and genuine stereoisomer of Aerangis lactone.