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. (C) 2014 Elsevier Ltd. All rights reserved.