title: 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 (-)-(2S,6 R)-cis-γ-Irone.
abstract: We report a simple, highly stereoselective synthesis of (+)-(S)-γ-ionone and (-)-(2S,6R)-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 AgSbF6 in 100:1 butan-2-one/H2O, proved to efficiently promote the Meyer-Schuster rearrangement of propargylic benzoates, whereas the digold catalyst [{Au(IPr)}2(μ-OH)][BF4] in anhydrous dichloromethane selectively promoted the oxy-Cope rearrangement of propargylic alcohols.
authors: Dipartimento di Chimica - Sezione Chimica Organica, Università degli Studi di Pavia, Via Taramelli 12, 27100 Pavia (Italy).
authors: Serena
authors: S
authors: Bugoni
authors: Dipartimento di Chimica - Sezione Chimica Organica, Università degli Studi di Pavia, Via Taramelli 12, 27100 Pavia (Italy).
authors: Valentina
authors: V
authors: Merlini
authors: Dipartimento di Chimica - Sezione Chimica Organica, Università degli Studi di Pavia, Via Taramelli 12, 27100 Pavia (Italy).
authors: Alessio
authors: A
authors: Porta
authors: EaStCHEM School of Chemistry, University of St. Andrews, North Haugh, KY16 9ST St. Andrews (UK).
authors: Sylvain
authors: S
authors: Gaillard
authors: Dipartimento di Chimica - Sezione Chimica Organica, Università degli Studi di Pavia, Via Taramelli 12, 27100 Pavia (Italy).
authors: Giuseppe
authors: G
authors: Zanoni
authors: EaStCHEM School of Chemistry, University of St. Andrews, North Haugh, KY16 9ST St. Andrews (UK).|Chemistry Department, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia).
authors: Steven P
authors: SP
authors: Nolan
authors: Dipartimento di Chimica - Sezione Chimica Organica, Università degli Studi di Pavia, Via Taramelli 12, 27100 Pavia (Italy). vidari@unipv.it.
authors: Giovanni
authors: G
authors: Vidari
keywords: fragrances; gold; homogeneous catalysis; sigmatropic rearrangement; terpenoids