Stereochemistry of terpene derivatives. Part 8: synthesis of novel terpenoids from (1S,4R)- and (1R,4S)-fenchone and their comparative odour characteristics

O-alkylation of (+) and (−)-fenchone oximes with various alkyl halides led to 20 novel ethers. Better results were obtained when mild reaction conditions were employed (i.e., aprotic, polar solvent and room temperature). The hydrolytic kinetic resolution of the O-glycidyl derivative was carried out using cobalt-salen catalysts. The best results were obtained when using (−)-(R,R)-catalyst: (−)-(R)-isomer was obtained with >90% de. The use of a (+)-(S,S)-catalyst gave the (−)-(S)-epoxide with only 67% de. However, the (S)-epoxide was obtained with >90% de when the (−)-(R)-diol was subjected to the Mitsunobu reaction. Significant fragrance diversity was observed between the homologous series of fenchone oxime ethers. More agreeable are scents of ethers derived from (−)-fenchone oxime. Their odours range from turpentine like and resinous to vegetable, floral or woody whereas the scents of (+)-ethers range from turpentine, resinous to onion like and slightly floral.

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(−)-(1R,4S)-1,3,3-Trimethylbicyclo[2.2.1]heptane-2-one oxime O-(2′R)-glycidyl etherC13H21NO2Ee > 90%[α]D24 = −28 (c 2.4, CHCl3)Source of chirality: (−)-(1R,4S)-1,3,3-Trimethylbicyclo[2.2.1]heptane-2-oneAbsolute configuration: (1R,4S,2′R)

(−)-(1R,4S)-1,3,3-Trimethylbicyclo[2.2.1]heptane-2-one oxime O-(2′S)-glycidyl etherC13H21NO2Ee > 90%[α]D24 = −41 (c 1.7, CHCl3)Source of chirality: (−)-(1R,4S)-1,3,3-Trimethylbicyclo[2.2.1]heptane-2-oneAbsolute configuration: (1R,4S,2′S)

(−)-(1R,4S)-1,3,3-Trimethylbicyclo[2.2.1]heptane-2-one oxime O-(2′S)-2′,3′-dihydroxypropyl etherC13H23NO3Ee > 90%[α]D24 = −28 (c 2.2, CHCl3)Source of chirality: (−)-(1R,4S)-1,3,3-Trimethylbicyclo[2.2.1]heptane-2-oneAbsolute configuration: (1R,4S,2′S)

(+)-(1S,4R)-1,3,3-Trimethylbicyclo[2.2.1]heptane-2-one oxime O-methyl etherC11H19NOEe = 100%[α]D25 = +52 (c 2.1, CHCl3)Source of chirality: (+)-(1S,4R)-1,3,3-Trimethylbicyclo[2.2.1]heptane-2-oneAbsolute configuration: (1S,4R)

(+)-(1S,4R)-1,3,3-Trimethylbicyclo[2.2.1]heptane-2-one oxime O-ethyl etherC12H21NOEe = 100%[α]D25 = +51 (c 2.6, CHCl3)Source of chirality: (+)-(1S,4R)-1,3,3-Trimethylbicyclo[2.2.1]heptane-2-oneAbsolute configuration: (1S,4R)

(+)-(1S,4R)-1,3,3-Trimethylbicyclo[2.2.1]heptane-2-one oxime O-propyl etherC13H23NOEe = 100%[α]D25 = +48 (c 2.4, CHCl3)Source of chirality: (+)-(1S,4R)-1,3,3-Trimethylbicyclo[2.2.1]heptane-2-oneAbsolute configuration: (1S,4R)

(+)-(1S,4R)-1,3,3-Trimethylbicyclo[2.2.1]heptane-2-one oxime O-allyl etherC13H21NOEe = 100%[α]D25 = +48 (c 2.4, CHCl3)Source of chirality: (+)-(1S,4R)-1,3,3-Trimethylbicyclo[2.2.1]heptane-2-oneAbsolute configuration: (1S,4R)

(+)-(1S,4R)-1,3,3-Trimethylbicyclo[2.2.1]heptane-2-one oxime O-propargyl etherC13H21NOEe = 100%[α]D25 = +48 (c 2.4, CHCl3)Source of chirality: (+)-(1S,4R)-1,3,3-Trimethylbicyclo[2.2.1]heptane-2-oneAbsolute configuration: (1S,4R)

(+)-(1S,4R)-1,3,3-Trimethylbicyclo[2.2.1]heptane-2-one oxime O-(2′RS)-glycidyl etherC13H21NO2Ee = 100%[α]D24 = +46 (c 2.4, CHCl3)Source of chirality: (+)-(1S,4R)-1,3,3-Trimethylbicyclo[2.2.1]heptane-2-oneAbsolute configuration: (1S,4R,2′RS)

(+)-(1S,4R)-1,3,3-Trimethylbicyclo[2.2.1]heptane-2-one oxime O-butyl etherC14H25NOEe = 100%[α]D25 = +44 (c 2.4, CHCl3)Source of chirality: (+)-(1S,4R)-1,3,3-Trimethylbicyclo[2.2.1]heptane-2-oneAbsolute configuration: (1S,4R)

(+)-(1S,4R)-1,3,3-Trimethylbicyclo[2.2.1]heptane-2-one oxime O-amyl etherC15H27NOEe = 100%[α]D25 = +41 (c 2.3, CHCl3)Source of chirality: (+)-(1S,4R)-1,3,3-Trimethylbicyclo[2.2.1]heptane-2-oneAbsolute configuration: (1S,4R)

(+)-(1S,4R)-1,3,3-Trimethylbicyclo[2.2.1]heptane-2-one oxime O-isoamyl etherC15H27NOEe = 100%[α]D25 = +40 (c 2.3, CHCl3)Source of chirality: (+)-(1S,4R)-1,3,3-Trimethylbicyclo[2.2.1]heptane-2-oneAbsolute configuration: (1S,4R)

(+)-(1S,4R)-1,3,3-Trimethylbicyclo[2.2.1]heptane-2-one oxime O-hexyl etherC16H29NOEe = 100%[α]D25 = +38 (c 2.3, CHCl3)Source of chirality: (+)-(1S,4R)-1,3,3-Trimethylbicyclo[2.2.1]heptane-2-oneAbsolute configuration: (1S,4R)