Improved Practical Synthsis of the Sex Pheromone of Female Sweet Potato Weevil, Cyals Formicarius

An improved synthesis of (Z)-dodec-3-en-1-yl (E)-2-butenoate (1), the female sex pheromone of sweet potato weevil, Cylas Formicarius, was reported. The synthesis bypassed the utilization of carcinogenic ethylene oxide, highly toxic HMPA, highly hydroscopic and unrecyclable DMPU, ethylene diamine, and liquid ammonia, for the alkylation of terminal alkyne. Instead, NaI was used to serve as a good nucleophile for alkyl bromide and a good leaving group for 1-lithiated alkyne. A safer and stereoselective palladium-catalyzed transfer semihydrogenation, using KOH/DMF as the hydrogen source, was employed for alkyne cis-hydrogenation, without using molecular hydrogen. The total yield was 62% over 5 steps, and the sex pheromone 1 obtained was verified spectroscopically. Field test results showed that the synthetic sex pheromone 1 was as effective as the commercial source or the sample provided by other research group.