A Facile Asymmetric Synthesis of(S)-14-methyl-1-octadecene, the Sex Pheromone of the Peach Leafminer Moth
|School||Northwest University of Science and Technology|
|Keywords||(S)-14-methyl-1-octadecene Asymmetric synthesis Peach leafminermoth (S)-4-benzyloxazolidin-2-one|
Nowadays, there is a sharp conflict between intense agricultural production andenvironmental issues. We all are facing a big challenge caused by the detrimental effectsresulting from traditional agricultural production. Therefore, there is an urgent need todevelop more green production modes, such as the use of environmentally benign,low-dosage sex pheromones to control pests. This mode plays an important role in so-calledIntegrated Pest Management. However, the existing synthetic pathways have some drawbackssuch as requiring too many chemical operations or low yield or lack of cost-effectiveness, sothe development of a more economical synthesis in consideration of applying this kind ofchemical in the pesticide industry is highly desirable.The peach leafminer moth, Lyonetia clerkella, is one of the most destructive pests inpeach orchards in China. The sex pheromone of peach leafminer was first identified as14-methyl-1-octadecene, and the activity of S-isomer from nature is higher. The paperenvisaged the first time a substrate-control asymmetric synthesis strategy of the sexpheromone of peach leafminer moth in the use of from commercially available inexpensiveEvans solvent (S)-4-benzyloxazolidin-2-one. And we provided an efficiently cheap and lesschemical operations synthesis protocol of the type of compounds, as well as expand theproduction and application to the pheromone.First, the target molecule1was disconnected into a chiral synthon A1and a C12moiety.The hexanoyl chloride from commercially available solvent was connected with Evanssolvent (S)-4-benzyloxazolidin-2-one, after chiral methylation achieved in the presence of astrong base such as LDA in78%yield. Then the chiral oxazolidine auxiliary was smoothlyremoved to get compound8by LAH reduction at10°C. However, in attempting to purifycompound8in the laboratory, this was found to be very laborious and less effective, so thecrude8was directly treated with TsCl, thus the chiral key intermediate A1was obtained in55%yield in two steps. Then the C12intermidate2moiety in turn could be disconnected intotwo parts C9+C3. We used1,9-Nonanediol as starting material which was selectivelybrominated under optimum conditions in89%yield, THP protected and converted into a Grignard reagent and this was coupled with C3subunit allyl bromide under Li2CuCl4catalysis to form a C12intermediate in66%yield. Afterwards, the THP group was removedin methanol in the presence of4-methyl-benzenesulfonic acid and was brominated by meansof PPh3/CBr4and was converted into a Grignard reagent. At last the target molecule,(S)-14-methyl-1-octadecene, was obtained after the two parts A1and C12intermediate weresubjected to a second Li2CuCl4-mediated C-C coupling in65%yield. Thus, the asymmetrictotal synthesis of (S)-1in an overall yield of30.3%was achieved in six linear steps. Activityand process research of the sex pheromone of the peach leafminer moth are still continuing.