Pheromone synthesis. Part 258. Synthesis of the enantiomers of the beetle pheromones ethyl 4-methylheptanoate, 4-methyloctanoic acid and 4-methyl-1-nonanol, and HPLC analysis of their derivatives to determine their enantiomeric purities

The enantiomers of citronellal have been converted into the enantiomers of the following beetle pheromones: ethyl 4-methylheptanoate (produced by male Nicrophorus vespilloides), 4-methyloctanoic acid (produced by male Oryctes elegans), and 4-methyl-1-nonanol (produced by female Tenebrio molitor). The enantiomeric purities of the synthetic pheromones were determined by HPLC analysis of the corresponding acids after derivatization with Ohrui’s reagent [(S)-1-(anthracene-2,3-dicarboximido)-2-propanol]. The enantiomers of 4-methyl-1-nonanol could also be analyzed employing another Ohrui’s reagent [(1S,2S)-2-(naphthalene-2,3-dicarboximido)cyclohexane-1-carboxylic acid].

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Ethyl (R)-4-methylheptanoateC10H20O2[α]D26 = −2.23 (c 5.02, hexane)Source of chirality: (S)-citronellalAbsolute configuration: (R)

(R)-4-Methyloctanoic acidC9H18O2[α]D27 = −2.33 (c 4.72, hexane)Source of chirality: (S)-citronellalAbsolute configuration: (R)

(S)-4-Methyl-1-nonanolC10H22O[α]D26 = −1.51 (c 4.63, hexane)Source of chirality: (R)-citronellalAbsolute configuration: (S)