1,720,958 research outputs found
A General and Concise Enantioselective Divergent Approach to 13-Alkyl-Substituted Ionones
No full textA novel enantioselective divergent route to 13-alkyl derivatives of alpha- and gamma-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)-a-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
Enantioselective Divergent Synthesis of (−)-cis-α- and (−)-cis-γ-Irone by Using Wilkinson’s Catalyst
No full textA simple, efficient synthesis is reported for (-)-cis- a- and (-)-cis-g-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-AuI-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 ste- reochemical aspects of this reaction are rationally supported by DFT calculation of the conformers of the substrates un- dergoing the hydrogenation and by a modeling study of the geometry of the rhodium h2 complexes involved in the dia- stereodifferentiation of the double bond faces. Thus, compu- tational investigation of the h2 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
The Importance of the 5-Alkyl Substituent for the Violet Smell of Ionones: Synthesis of Racemic 5-Demethyl-α-ionone
No full textThe synthesis and the odor tonalities of racemic 5-demethyl-α-ionone are described. This synthetic ionone derivative did not show the typical floral-woody violet smell of α-ionone, definitely proving the importance of a suitably sized and spatially oriented alkyl substituent at C(5) for stimulating olfactory receptors of ionones
Dual ReV Catalysis in One-Pot Consecutive Meyer–Schuster and Diels–Alder Reactions
No full textA 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 reac- tions 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 com- putational studies of the cycloaddition mechanism provided the preferred geometry of the rhenium complex in the transi- tion state (TS) and corroborated the experimental endo select- ivity
A new ursane-type triterpenoid and other constituents from the leaves of Crataegus azarolus var. aronia
No full textA new ursane-type triterpene acid, named azarolic acid (1), along with four
known phenolic compounds and four known triterpene acids, was isolated from the crude
EtOAc extract of the leaves of Crataegus azarolus var. aronia L. The structure of 1 was
determined from 1D and 2D NMR spectroscopic data. Euscaphic acid showed high
anti-vasoconstriction effects on aortic rings, supporting the use of this medicinal plant in
cardiovascular disease
Competitive gold-promoted Meyer-Schuster and oxy-Cope rearrangements of 3-acyloxy-1,5-enynes : selective catalysis for the synthesis of (+)-(S)-gamma-ionone and (-)-(2S,6R)-cis-gamma-irone
No full textWe report a simple, highly stereoselective synthesis of (+)-(S)-gamma-ionone and (-)-(2S,6R)-cis-gamma-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)(mu-OH)][BF4] in anhydrous dichloromethane selectively promoted the oxy-Cope rearrangement of propargylic alcohols
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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