Absolute configuration and synthesis of β- and δ-lactones present in the pheromone system of the giant white butterfly Idea leuconoe

Males of the giant white butterfly Idea leuconoe release a complex mixture of compounds during courtship. Besides alkaloids, aromatics, terpenoids and hydrocarbons, several lactones have been identified in the pheromone bouquet. Two simple stereoselective methods to create the lactones in good enantiomeric excesses have been developed. The generation of the stereocenters of the beta-lactones 1a and 1b is based on a controlled C-C coupling by a Horner-Wadsworth-Emmons approach, followed by asymmetric dihydroxylation, whereas the synthesis of the delta-lactone 3b uses an enantioselective hydrogenation of a dioxoalkanoate precursor. The absolute configurations of the natural lactones 1a, 1b and 3b were determined by gas chromatography on a chiral stationary phase. Both 1a and 1b are of (S,S) configuration, suggesting their biosynthetic origin from (-)-viridifloric acid (7a) or (-)norviridifloric acid (7b), respectively. In contrast, natural 3b is a mixture of all enantiomers, in which the (5S,7S) enantiomer dominates.