Internal Nucleophilic Termination in Acid‐Mediated Polyene Cyclizations Part 4

Abstract

Abstract Treatment of the unsaturated bicyclic homoallylic alcohols ( E )‐ and ( Z )‐ 5 and ( Z )‐ and ( E )‐ 10 and allenic alcohol 16 with an excess of ClSO 3 H in 2‐nitropropane or CH 2 Cl 2 at − 80° afforded, in moderate yields ( ca. 30–70%), diastereoisomer mixtures of racemic tetracyclic ethers 12a – c ( Table 1 ) and 17a,b ( Table 2 ), respectively. These kinetically controlled stereospecific transformations are believed to proceed via concerted or nonconcerted pathways (see Schemes 4 and 6 ) and the results are fully consistent with our earlier work. Representing novel didehydro bridged analogues of known, olfactively active labdane tricyclic ethers, the organoleptic properties of 12a – c and 17a,b are briefly described, especially those of 12c which, in the context of structure–activity studies, is a racemic didehydro analogue of the known ambergris odorant Ambrox ® .