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Competitive Gold‐Promoted Meyer–Schuster and oxy‐Cope Rearrangements of 3‐Acyloxy‐1,5‐enynes: Selective Catalysis for the Synthesis of (+)‐( S )‐γ‐Ionone and (−)‐(2 S ,6 R )‐ cis ‐γ‐Irone
Author(s) -
Bugoni Serena,
Merlini Valentina,
Porta Alessio,
Gaillard Sylvain,
Zai Giuseppe,
Nolan Steven P.,
Vidari Giovanni
Publication year - 2015
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201502382
Subject(s) - chemistry , catalysis , medicinal chemistry , dichloromethane , anhydrous , cope rearrangement , stereochemistry , organic chemistry , solvent
We report a simple, highly stereoselective synthesis of (+)‐( S )‐γ‐ionone and (‐)‐(2 S ,6 R )‐ cis ‐γ‐irone, two characteristic and precious odorants; the latter compound is a constituent of the essential oil obtained from iris rhizomes. Of general interest in this approach are the photoisomerization of an endo trisubstituted cyclohexene double bond to an exo vinyl group and the installation of the enone side chain through a [(NHC)Au I ]‐catalyzed Meyer–Schuster‐like rearrangement. This required a careful investigation of the mechanism of the gold‐catalyzed reaction and a judicious selection of reaction conditions. In fact, it was found that the Meyer–Schuster reaction may compete with the oxy‐Cope rearrangement. Gold‐based catalytic systems can promote either reaction selectively. In the present system, the mononuclear gold complex [Au(IPr)Cl], in combination with the silver salt AgSbF 6 in 100:1 butan‐2‐one/H 2 O, proved to efficiently promote the Meyer–Schuster rearrangement of propargylic benzoates, whereas the digold catalyst [{Au(IPr)} 2 (μ‐OH)][BF 4 ] in anhydrous dichloromethane selectively promoted the oxy‐Cope rearrangement of propargylic alcohols.