Scale white peach

Asymmetric syntheses directed toward construction of enantiomers of the western and southern corn root-worm pheromones are described. A brief review of the subject of asymmetric synthesis as it is related to the synthesis of insect sex pheromones is presented. The laboratory s previous research with chiral pheromones is summarized (Japanese beetle, white peach scale, and lesser tea tortrix) before detailing synthetic work on the pheromones of the aforementioned rootworm species. Throughout the course of the synthetic effort, cholesteric stationary phases for GLC have found use. Their superior ability to separate crucial diastereomeric intermediates for synthesis is detailed. 

White peach scale. Several scale sex pheromones have now been elucidated each of them possesses an asymmetric center and usually a trisubstituted alkene link within an isoprenoid framework (43). The structure of the white peach scale pheromone, R,Zb-II (Figure 8), lent itself to synthesis with another chiral starting material, namely limonene (44). Selective ozonlysis followed by workup with dimethyl sulfide-methanol provided a ketoacetal, III. Wittig methylenation followed by hydrolytic cleavage of the acetal gave a dienaldehyde, IV. Conversion of the aldehyde via the acid to an amide (45) with enantiomerically pure ot-methylbenzylamine permitted chromatographic assessment of the purity of the diene aldehyde (and the limonene). The required R-isomer of the diene aldehyde was >48% ee. 

Figure 8. Limonene as a chiral starting material for white peach scale sex pheromone.

Only the R.jJ-stereoisomer elicits sexual response from male white peach scale, the other isomers have no biological activity nor do they affect the activity of the R,Z-isomer. 

The four stereoisomers of 3, 9-dimethyl-6-(1-methylethenyl)-3,9-decadien-1-ol propanoate (61), the pheromone of the white peach scale, Pseudaulaaaspis pentagona, been obtained from (i )-( + )-and (S)-... 

A new method for preparing Z-homoallylic alcohols, involving the SCOOP Y modification of the Wittig reaction, has been developed as part of a synthesis of the sex pheromone of the White Peach Scale (Scheme 65). Although the... 

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