- The enantiomers of Iralia: preparation and odour evaluation
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The enantiomers of methyl ionones 1 and 2 were prepared by an enzyme-catalysed approach. Their odour properties were evaluated by skilful perfumers.
- Abate, Agnese,Brenna, Elisabetta,Fuganti, Claudio,Malpezzi, Luciana,Serra, Stefano
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p. 1145 - 1153
(2008/02/10)
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- 4,5-Didehydro-9-demethyl-9-halo-5,6-dihydroretinals and their 9-cyclopropyl and 9-isopropyl derivatives - Simple preparation of α-ionone derivatives and pure (all-E)-, (9Z)- and (11Z)-α-retinals
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α-Ionone and several of its chemically modified derivatives have been prepared in high yield in full isomeric purity by a Wadsworth-Emmons procedure using imino-phosphonate anion reagents. Starting from α-ionone, 5-(2′,6′,6′-trimethylcyclo-2′-hexen-1′-yl) -4-penten-2-yn-1-al could be prepared in a high yielding one-pot procedure. The corresponding (9-Cl-, 9-Br- and 9-I-α-ionylidene)acetaldehyde system could be obtained in one step in a quantitative mixture of (9Z) and (all-E) isomers by 1,4-nucleophilic addition reactions. The pure (all-E) and (9Z) isomers could be separated by simple column chromatography. The corresponding [(9Z)- and (all-E)-9-demethyl-9-fluoro-α-ionylidene]acetaldehydes could also be obtained in pure form by simple column chromatography. These α-ionylidene systems could be easily converted either into the (all-E)-4,5-didehydro-9- demethyl-9-halo-5,6-dihydroretinals or the corresponding (9Z) isomers in two steps. Similar mixtures of the corresponding (9Z,11Z)-and (9Z)-nitriles could be obtained by normal chemistry. The (9Z,11Z) isomer is the main component of this mixture, and could be obtained in pure form. Subsequent reduction with DIBAL-H and careful workup gave the pure (9Z,11Z)-9-halo-retinals. These (9Z,11Z) isomers show a similar extreme acid sensitivity to the corresponding 9-halo-β-retinals. α-Retinal and its 9-demethyl, 19,19-ethano and 19,19-dimethyl derivatives have been prepared in the (all-E), (9Z), and (11Z) isomeric forms in a similar manner. The corresponding β-retinal and its 9-demethyl derivative in the various isomeric forms are known. In this paper the 19,19-ethano- and 19,19-dimethyl-β-retinals in the (all-E), (9Z), and (11Z) isomeric forms are also reported. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.
- Wang, Yajie,Lugtenburg, Johan
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p. 3497 - 3510
(2007/10/03)
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- Photochemical Reactions. 148th Communication. Photochemistry of Acylsilanes: Preparation, Photolyses, and Thermolyses of α,β-Unsaturated Silyl Ketones
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The syntheses, photolyses, and thermolyses of the α,β-unsaturated silyl ketones (E/Z)-7, (E)-8, and (E)-9 are described.On n,?*-excitation (λ > 347 mm), the aforementioned compounds undergo (E/Z)-isomerization followed by γ-H abstraction.The intermediate enols are trapped intermolecularly by siloxycarbenes leading to the dimeric acetals 27A + B, 30A + B, and 31A + B.In addition, the acylsilanes (E/Z)-7 undergo photoisomerization by δ-H abstraction furnishing the acylsilanes 29A + B.Flash vacuum thermolyses (FVT) of (E/Z)-7, (E/Z)-8, and (E)-9 give rise to intramolecular reactions of the siloxycarbene intermediates.Thus, FVT (520 deg) of (E)- and (Z)-7 selectively leads to the enol silyl ethers 32 and (E)-33, respectively, arising from carbene insertion into an allylic C-H bond.FVT of (E/Z)-8 (560 deg) and (E)-9 (600 deg) affords the trienol silyl ethers 34A + B and the cyclic silyl ethers 37A + B, respectively, which are formed by CH insertion of the siloxycarbenes.As further products of (E)-8 and (E)-9, the bicyclic enol ethers 35 and 36 are formed, presumably via siloxycarbene addition to the cyclohexene C=C bond.
- Scheller, Markus E.,Iwasaki, Genji,Frei, Bruno
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p. 1378 - 1394
(2007/10/02)
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