Stereochemistry‐Odor Relationships in Enantiomeric Ambergris Fragrances

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Abstract
Twelve tricyclic ethers of the labdane and ent‐labdane series, 5–16, have been synthesized; compounds 6–15 are new. The intramolecular C18‐acetals 1–4 and the tricyclic ethers 5–16 were submitted to an olfactory test which was characterized by an exceptionally high percentage of ‘wrong’ answers (cf. Table 1, footnote b). For most compounds specific anosmia, rapidly ensuing fatigue and a high percentage of odor deviation were the most salient features.Pronounced ambergris‐like odors were only noted in compounds of the labdane series, and were strongest in ethers 1, 5 and 15, followed by the ethers 9 and 11. In contrast, both labdane derivatives 3 and 7 were practically odorless. Their enantiomers 4 and 8, on the other hand, have relatively strong odors which can only to a limited extent be associated with ambergris‐type odors. The pairs of ethers 3/4 and 7/8 are the first recorded examples of optical antipodes in which only one isomer possesses olfactory properties.