Synthesis of [4.3.3]Propellanes by Carbenium-Ion Rearrangement and Their Olfactory Characterization

✍ Scribed by Georg Fráter; Daniel Helmlinger; Philip Kraft

• Publisher: John Wiley and Sons
• Year: 2003
• Tongue: German
• Weight: 302 KB
• Volume: 86
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.200390067

✦ Synopsis

Abstract

Treatment of (+)‐sclareolide (1) with polyphosphoric acid or __Eaton'__s reagent furnished, besides the anticipated cyclopentenone (−)‐12 and its isomer (−)‐15, two diastereoisomeric [4.3.3]propellanes (−)‐13 and (−)‐14, which possess interesting woody‐ambery odors. The hydrogenated derivative (−)‐17 possessed an even more‐powerful odor reminiscent of natural ambergris tincture. Mechanistic insight into this rearrangement was provided by a by‐product 24 of the reaction of sclareolide (1) with __Eaton'__s reagent. The carbenium ion rearrangement was then employed in the synthesis of four related [4.3.3]propellanes 40–43, illustrating the utility and scope of this reaction. The olfactory properties of the synthesized [4.3.3]propellanes as well as of the original target structures 10, 33, and 34, prepared from (−)‐12 and (−)‐15, are discussed. Especially the pronounced ambra odor of (−)‐17 vividly contradicts the ‘triaxial rule of amber sensation' and provides new insight into the structural requirements for ambra odorants.