Absolute Configuration and Synthesis of 2‐Hydroxy‐2‐(1‐hydroxyethyl)‐3‐methyl‐γ‐butyrolactone, a Presumed Pheromone of Ithomiine Butterflies

2‐Hydroxy‐2‐(1‐hydroxyethyl)‐3‐methyl‐γ‐butyrolactone ( 1 ) is a constituent of scent glands of male ithomiine butterflies. All diastereomers and the respective (3 R )‐enantiomers were synthesized by starting from rac ‐ or (3 S )‐3‐methyl‐γ‐butyrolactone 3 . Their relative configurations were determined by difference NOE‐NMR spectroscopy or by X‐ray diffraction analysis. The absolute configuration of the natural product was determined by gas chromatography on a chiral stationary phase of the respective dioxolane derivatives. The natural lactone could be shown to be the (1′ S ,2 S ,3 R )‐enantiomer [(1′ S ,2 S ,3 R )‐ 1a , ithomiolide A]. In addition, the corresponding ketone, (2 S ,3 R )‐2‐acetyl‐2‐hydroxy‐3‐methyl‐γ‐butyrolactone [(2 S ,3 R )‐ 5a , ithomiolide B], could be identified as a new natural product from Prittwitzia hymaenea .