Synthesis of (1S,4R)-4-isopropyl-1-methyl-2-cyclohexen-1-ol, the aggregation pheromone of the ambrosia beetle Platypus quercivorus, its racemate, (1R,4R)- and (1S,4S)-isomers

(S)-Perillyl alcohol was converted to (R)-cryptone (91.5–93% ee) in six steps, which was then treated with methyllithium to give (1S,4R)-4-isopropyl-1-methyl-2-cyclohexen-1-ol, the aggregation pheromone of the ambrosia beetle Platypus quercivorus. The racemic pheromone was also prepared by methylation of (±)-cryptone. Both (1R,4R)- and (1S,4S)-isomers (98% ee) of the pheromone were synthesized from the enantiomers of dihydrolimonene oxide.

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(R)-CryptoneC9H14OEe = 91.5% (chiral GC)[α]D19=-86.8 (c 1.06, EtOH)Source of chirality: (S)-perillyl alcoholAbsolute configuration: R

(1S,4R)-4-Isopropyl-1-methyl-2-cyclohexen-1-olC10H18OEe = 93.3% (chiral GC)[α]D19=-68.7 (c 1.42, hexane)Source of chirality: (S)-perillyl alcoholAbsolute configuration: 1S,4R

(1R,4R)-4-Isopropyl-1-methyl-2-cyclohexen-1-olC10H18OEe = 98.7% (chiral GC)[α]D22=+10.3 (c 4.28, hexane)Source of chirality: (R)-limonene oxideAbsolute configuration: 1R,4R