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

Abstract

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.