Significance of the Geminal Dimethyl Group in the Odor Principle of Ambrox®

The diastereoisomeric 18‐nor‐ and 19‐norambrox ((6α)‐ and (6β)‐dodecahydro‐3a,6,9a‐trimethylnaphtho[2,1‐b]furans resp.) as well as the corresponding 18,19‐dinor‐derivatives (dodecahydro‐3a,9a‐dimethylnaphtho[2,1‐b]furans) have been synthesized and subjected to sensory evaluation. Threshold data and odor determination give an enlarged insight into the structure‐activity relationship (SAR) in ambrox‐type ambergris fragrances. As a general conclusion, the accumulation of axial CH3 groups in the tricyclic ethers 1–12 leads to the strongest receptor affinity.