Synthesis of (1R,4R,5S)-(+)-Acoradiene, the Structure Proposed for the Aggregation Pheromone of the Broad-Horned Flour Beetle

(1R,4R,5S)-(+)-Acoradiene {1,8-dimethyl-4-(1'-methylethenyl)spiro[4.5]dec-'7-ene (1)}, the structure proposed for the aggregation pheromone of the broad-horned flour beetle (Gnatocerus cornutus), was synthesized from (R)-(+)-pulegone (2) by employing the ring-closing olefin metathesis of diene 9 as the key step, and confirming the structure of intermediate 11 by X-ray analysis. The spectral properties of (+)-1 were different from those reported for the pheromone, whose proposed structure 1 was therefore proven incorrect.