Synthesis of the sex pheromone components of fall armyworm (Spodoptera frugiperda)

Abstract

Main components of the sex pheromone of fall armyworm (Spodoptera frugiperda) contain (Z)-7-dodecen-1-yl acetate (Z7-12:OAc), (Z)-9-tetradecen-1-yl acetate (Z9-14:OAc), and (Z)-11-hexadecen-1-yl acetate (Z11-16:OAc) were succesfully synthesized with a total yield over 48% via 5 steps. The starting materials for the synthesis of pheromones were diols (1,6-hexandiol; 1,8-octandiol; 10-decandiol) and 1-alkyne (1-hexyne and 1-octyne). This purpose of the study was the extension of the carbon chain by alkylation of a terminal alkyne using the n-BuLi agent and the reduction of alkyne to (Z)-alkene using the Pd(dba)2/KOH/DMF catalyst without using the molecular hydrogen. In this case, KOH/DMF was the hydrogen source system to eliminate an alkyne to (Z)-alkene and give over 90% yield with the (Z)-configuration selectivity (> 99%). The extension reaction of the carbon chain was carried out at -78oC for 30 min. and then at room temperature for 2 h., the alkyne was reduced to (Z)-alkene at 145oC for 6 hours. After the deprotection of the alcohol group by ultrasound without further purification, the acetylation was performed with an efficiency over 84%. The (Z)-alkene configuration of the obtained compounds, examined by 1H NMR spectra, showed that the coupling constants were Jcis = 11,0 Hz and Jcis = 10,5 Hz for Z11-16:OAc, respectively; but Jcis = 11,0 Hz for the Z7-12:OAc and Z9-14:OAc. This preparation process of the (Z)-alkene pheromones opened an opportunity to control fall armyworms without polluting the environment in Vietnam.