Synthesis of Enantiomerically Pure Pheromones of South‐Pacific Brown Algae: Hormosirene and Dictyopterene A

Hormosirene ((−)‐1; (1R,2R)‐1‐((1E,3Z)‐1,3‐hexadienyl)‐2‐vinylcyclopropane) is the specific sex attractant of several brown algae of the Australian shelf, while dictyopterene A ((+)‐2; (1R, 2R)‐1‐((1E)‐1‐hexenyl)‐2‐vinylcyclopropane) is found as a minor constituent of the pheromone bouquets. The asymmetric synthesis of the two hydrocarbons is performed by resolution of the amides (−)‐5 and (+)‐5a obtained from (−)‐(R)‐2‐phenylglycinol and racemic trans‐vinylcyclopropanecarboxylic acid (rac‐4) on silica gel. Both diastereoisomers are obtained optically pure. They are converted by stereoselective Wittig olefination into the title compounds. Compound (−)‐1 is the active mating pheromone of the reproductive system of the seaweed Xiphophora chondrophylla as established by biological‐activity assays.