Pheromone synthesis. Part 240: Cross-metathesis with Grubbs I (but not Grubbs II) catalyst for the synthesis of (R)-trogodermal (14-methyl-8-hexadecenal) to study the optical rotatory powers of compounds with a terminal sec-butyl group

(R)-Trogodermal (14-methyl-8-hexadecenal), the sex pheromone of Trogoderma species of pest insects against stored products, and its (S)-isomer were synthesized by using olefin cross-metathesis between (R)- or (S)-7-methyl-1-nonene and 8-nonenyl acetate as the key step. This step was successful with Grubbs I but not with Grubbs II catalyst. The latter caused randomization of the carbon skeleton to give a mixture of abnormal products with both longer or shorter carbon chains than the desired product. The specific rotations of 18 newly and 6 previously synthesized compounds with a terminal sec-butyl group were measured to conclude them to be [α]D +3.5 to +6.5 or −3.6 to −6.4.