Syntheses of some insect pheromones

Ekanayake, Neelakanthie (1982) Syntheses of some insect pheromones. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

A short synthesis of perillen, the pheromone isolated from the Formicine ant Lasius (Dendrolasius) fulignosus and from some of the ants belonging to the tribe Tetramorini has been achieved via the coupling reaction between n-I,1-dimethylallylnickel bromide complex and 3-bromomethylfuran. This reaction was found to give rise to a bis-furano compound in addition to the bis-allyl compound usually resulting from these coupling reactions. Stereospecific allylic oxidation of perillen with selenium dioxide-pyridine resulted in formation of trans-perillenal, the pheromone of the pine saw fly, Neodiprion sertifer, Geoffr. Attempts have also been made to synthesise ipsdienol, the major component in the aggregation pheromone system of bark beetles of the family Scolytidae, by the coupling between v-2-ethenylallylnickel bromide complex and 3-methyl-2-butenai. This complex was shown to be inert towards carbonyl compounds and to have only moderate reactivity towards reactive halides. An approach to the synthesis of faranal, the trail pheromone of the ant Monomorium Pharaonis employing Wittig reaction as the key step, has been made. In this convergent synthesis one half of the target molecule (Z)-7-bromo-3-methyl-3-octene was prepared following a literature procedure while the required carbon skeleton for the other half 3,4-dimethyl-6-(tetrahydro-2H-pyranyloxy)hexane-l-al, was prepared using electrochemical dimerization of ethyl crotonate. The stereochemical outcome of this electrochemical reaction was investigated and found to give rise to diastereomers. Model studies were carried out on the intended Wittig reaction and the modified Wittig procedures were found to have only a small effect on the stereospecific formation of trisubstituted double bonds. A short convergent synthesis for faranal was achieved via the coupling of 1(E), 5(Z)-l-iodo-2, 6-dimethylocta-l, 5-diene with 3, 4--Cc iimethyl-5-iodol (tetrahydro-ZH-pyranyloxy)pentane. The formation of these two compounds were achieved by the use of dimethyl sulphide stabilised cuprate reagents and urastereomers from the previously described electrochemical method respectively. The conventional route for the synthesis of cis-3, 4-dimethyl5-iodo-1{tetrahydro-ZH-pyranyloxy)pentane involving Diels-Alder addition of maleic anhydride and 1, 3-butadiene has also been improved to give a higher overall yield.

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