Efficient asymmetric synthesis of long chain methyl-branched hydrocarbons, components of the contact sex pheromone of females of the cerambycid beetle, Neoclytus acuminatus acuminatus

Both enantiomers of 7-methylheptacosane and 7-methylpentacosane, the major components of the female-produced contact sex pheromone of the red-headed ash borer beetle (Neoclytus acuminatus accuminatus) were synthesized in 62–68% overall yield (six steps) via alkynylation of the triflate of a shared chiral alcohol intermediate (R)- or (S)-2-methyloctanol. The enantiomers of the shared intermediate were prepared via acylation and subsequent asymmetic methylation of (R)- and (S)-4-isopropyloxazolidin-2-one chiral auxiliaries, respectively. The methodology can be readily adapted for the preparation of analogues with any desired chain length and methyl branch positions.

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(R)-2-Methyloctan-1-olC9H20OEe = >98%[α]D25=+13.16 ± 0.09 (c 1.5, EtOH) >98% ee from Chiral GC)Source of chirality: (R)-4-isopropyloxazolidin-2-oneAbsolute configuration: (R)

(R)-7-Methylheptacos-7-yneC28H54Ee = >98%[α]D22=-0.43 ± 0.019 (c 3.47, CH2Cl2)Source of chirality: asymmetric synthesisAbsolute configuration: (R)

(R)-7-Methylpentacos-7-yneC26H50Ee = >98%[α]D22=-0.42 ± 0.036 (c 3.51, CH2Cl2)Source of chirality: asymmetric synthesisAbsolute configuration: (R)

(R)-7-MethylheptacosaneC28H58Ee = >98%[α]D21=-0.247 ± 0.013 (c 3.75, CH2Cl2)Source of chirality: asymmetric synthesisAbsolute configuration: (R)

(R)-7-MethylpentacosaneC26H54Ee = >98%[α]D22=-0.253 ± 0.009 (c 3.56, CH2Cl2)Source of chirality: asymmetric synthesisAbsolute configuration: (R)