Bakers' yeast reduction of (2
E)-3-(2-furanyl)-2-methyl-2-propenal yielded the synthetic intermediate, (2
S)-3-(2-furanyl)-2-methylpropanol, of high chiral purity (>97% ee) for the synthesis of the enantiomers of 2,5-dimethylheptadecane and 7-methylheptadecane, two synergistic sex pheromone components of the western hemlock looper (WHL),
Lambdina fiscellaria lugubrosa Hulst. In electrophysiological bioassays, (7
S)- but not (7
R)-7-methylheptadecane elicited strong antennal responses by male WHL antennae. In field trapping experiments, addition of (7
S)- but not (7
R)-7-methylheptadecane to (5
R,11
S)-5,11-dimethylheptadecane, the major sex pheromone component of WHL, increased attraction. Attraction to (5
R,11
S)-5,11-dimethylheptadecane in combination with (7
S)-7-methyiheptadecane was further enhanced by the addition of (5
S)- but not (5
R)-2,5-dimethylheptadecane. Similarly, attraction to (5
R,11
S)-5,11-dimethylheptadecane combined with (5
S)-2,5-dimethylheptadecane increased when 7
S- but not (7
R)-7-methylheptadecane was added as a third component. We conclude that (7
S)-7-methylheptadecane and (5
S)-2,5-dimethylheptadecane are the synergistic sex pheromone components of WHL. The synthetic methodology described is applicable to the synthesis of chiral methyl-branched pheromones in other orders of the Insecta, particularly Coleoptera, Diptera and Orthoptera.
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