AbstractTreatment of the acyclic tetraenols (E)‐ and (Z)‐2 with an excess of ClSO3H in 2‐nitropropane at − 80° stereoselectively afforded in 30 and 43% yield, respectively, diastereoisomer mixtures of the racemic, tricyclic ethers 1c,d and 1a,b, together with 20 (Table). Under identical conditions, but with the acyclic pentaenol 10 (1 : 1 diastereoisomer mixture) as substrate, the tricyclic ethers 22a/22b (10 : 1) were isolated in 27% yield. These kinetically controlled stereospecific transformations are thought to proceed via non‐concerted pathways (see Schemes 5 and 7), fully consistent with our earlier work. In contrast, another set of reaction conditions (CF3CO2H, CH2Cl2, − 15° to − 10°) was used for the cyclization of the monocyclic dienols (E)‐3 and (Z)‐3, which resulted in the non‐stereoselective formation of the major products 1c,d and 1a,b, respectively, in 35–37% yield. Representing novel didehydro analogues of the known ambergris odorant (±)‐Ambrox® and its diastereoisomers, the qualitative organoleptic properties of 1a–d and of the 10 : 1 diastereoisomer mixture of the novel tetradehydro analogues 22a/22b are briefly described.