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Internal Nucleophilic Termination in Acid‐Mediated Polyene Cyclisations: Synthetic access to methyle homologs of (±)‐ Ambrox ® and its diastereoisomers
Author(s) -
Snowden Roger L.,
Eichenberger JeanClaude,
Giersch Wolfgang,
Thommen Walter,
SchulteElte Karl H.
Publication year - 1993
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19930760417
Subject(s) - chemistry , polyene , diastereomer , stereochemistry , nucleophile , organic chemistry , catalysis
Abstract Treatment of ten monocyclic dienols 8–11 with an excess of fluorosulfonic acid in 2‐nitropropane at −90° afforded diastereoisomeric mixtures of racemic tricyclic ethers 12–14 in 81–91% yield (see tables 1 and 2 ). These transformations represent further examples of biomimetic acid‐mediated cyclisations in which an OH group serves as the internal nucleophilic terminator. A non‐synchronous process is postulated, and the examples described strongly re‐inforce our working mechanistic hypothesis, whereby the stereochemical course of cyclisation is directed by the orientation of the side chain vicinal to the intermediate cyclohexyl cation ( see Schemes 4 and 5 ). It is also demonstrated that the efficiency of this process is independent of the nature of the OH group, which may be primary, secondary, or tertiary. In addition, the organoleptic properties of 12–14 , Me homologs of known odorants such as Ambrox® ((−)‐ 3a ) and its diastereoisomer, are briefly discussed.