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

Abstract 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 (3R)‐enantiomers were synthesized by starting from rac‐ or (3S)‐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,2S,3R)‐enantiomer [(1′S,2S,3R)‐1a, ithomiolide A]. In addition, the corresponding ketone, (2S,3R)‐2‐acetyl‐2‐hydroxy‐3‐methyl‐γ‐butyrolactone [(2S,3R)‐5a, ithomiolide B], could be identified as a new natural product from Prittwitzia hymaenea.