A simple, efficient synthesis is reported for (-)-cis-α- and (-)-cis-γ-irone, two precious constituents of iris oils, in ≥99 % diastereomeric and enantioselective ratios. The two routes diverge from a common intermediate prepared from (-)-epoxygeraniol. Of general interest in this approach is the installation of the enone moiety of irones through a NHCAu(I) -catalyzed Meyer-Schuster-like rearrangement of a propargylic benzoate and the use of Wilkinson's catalyst for the stereoselective hydrogenation of a prostereogenic exocyclic double bond to secure the critical cis stereochemistry of the alkyl groups at C2 and C6 of the irones. The stereochemical aspects of this reaction are rationally supported by DFT calculation of the conformers of the substrates undergoing the hydrogenation and by a modeling study of the geometry of the rhodium η(2) complexes involved in the diastereodifferentiation of the double bond faces. Thus, computational investigation of the η(2) intermediates formed in the catalytic cycle of prostereogenic alkene hydrogenation by using Wilkinson's catalyst could be highly predictive of the stereochemistry of the products.

A readily available oxo‐ReV catalyst has been shown to promote a one‐pot multistep process that involves the Meyer–Schuster rearrangement of alkynols followed by the Diels–Alder cycloaddition of the resulting enones. These reactions were performed under mild conditions in the presence of 5 mol‐% of the catalyst to afford the cycloadducts in good yields with almost 100 % endo stereoselectivity. In‐depth computational studies of the cycloaddition mechanism provided the preferred geometry of the rhenium complex in the transition state (TS) and corroborated the experimental endo selectivity.

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.

The synthesis and the odor tonalities of racemic 5-demethyl--ionone are described. This synthetic ionone derivative did not show the typical floral-woody violet smell of -ionone, definitely proving the importance of a suitably sized and spatially oriented alkyl substituent at C(5) for stimulating olfactory receptors of ionones.

A novel enantioselective divergent route to 13-alkyl derivatives of α- and γ-ionone, important components of perfumes and fragrances, is reported. This relatively short and convenient methodology takes advantage of the use of a common intermediate, easily obtained from highly enantiomerically enriched (S)-α-ionone, which avoids the separate installation of the butenone side chain at C(6) for each analog. Olfactory evaluation of synthesized compounds reconfirmed the influence of the hydrophobic interactions of alkyl substituents at C(5) with olfactory receptors (ORs) in the chemoreception of ionones, and suggested that a synperiplanar orientation of C(13) and the lateral chain is the better geometry fitting OR's cavity.