- ORGANIC COMPOUND USED AS FRAGRANCE INGREDIENTS
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A compound of formula I wherein R1, R2, R3 and R4 can be independently selected from H or Me, n = 0, 1, the dotted lines are indicating single bonds, or in case n = 0 an isolated double bond at position 3', or in case n = 1 an isolated double bond at position 3' or 4', and the wavy bond is indicating an unspecified configuration of the adjacent double bond. Said compounds, as well as precursors capable to generate said compounds, are useful as fragrance ingredients.
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- Investigations into the selective oxidation of vicinal diols to α-hydroxy ketones with the NaBrO3/NaHSO3 reagent: PH dependence, stoichiometry, substrates and origin of selectivity
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The NaBrO3/NaHSO3 reagent is one of the few oxidizing agents that chemoselectively oxidizes vicinal diols to α-hydroxy ketones with little overoxidation to the corresponding vicinal-dione or dicarboxylic acid. Oxidation reactions performed with this reagent showed strong pH dependence. cis-Vicinal diols reacted faster than trans-vicinal diols to the α-hydroxy ketone product. Hydroxy functional groups at axial ring positions were more readily oxidized than equatorial hydroxy groups. The application of the NaBrO3/NaHSO3 reagent for the chemoselective oxidation of vicinal diols was limited to simple systems and failed with more complex monosaccharide compounds probably due to acid catalyzed dehydrogenation reactions. Despite the simple reaction set-up and good selectivity towards the α-hydroxy ketone product, the actual oxidation reaction mechanism is highly complex and postulated to involve at least six different equilibria with a plethora of bromine containing species. A possible oxidation reaction mechanism is discussed.
- Bierenstiel, Matthias,D'Hondt, Paul J.,Schlaf, Marcel
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p. 4911 - 4917
(2007/10/03)
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- 5-exo-trig Versus 6-endo-trig cyclization of Alk-5-enoyl radicals: The role of one-carbon ring expansion
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Alk-5-enoyl radicals were made to cyclize in exo and endo modes to give the corresponding cycloketone radicals, which are related through one-carbon ring expansion. Relative kinetic data were determined for the ring closure of the 2-methylhept-5-enoyl radical generated by the reaction of the corresponding phenyl-seleno ester with Bu3SnH over the temperature range 233-323 K. The conversion to absolute rates provided Arrhenius expressions for the 5-exo-trig and 6-endo-trig cyclizations. Ab initio and semiempirical (AM1) calculations were performed on the hex-5-enoyl and hept-5-enoyl radicals, respectively, and the outcomes aided in the rationalization of the preexponential factors and activation energies. Both 1,5- and 1,6-ring closure occur via in a lower energy 'chairlike' transition state. The observed high regioselectivity is due to favorable entropic and enthalpic factors associated with the formation of the smaller ring. The stereoselectivity was higher in the 1,6-ring closure (70:30) than in the 1,5-ring closure (55:45), the trans isomer being predominant in both. For the one-carbon ring expansion studies, the radicals of interest were obtained by deoxygenation of suitable alcohols via the O-phenyl thiocarbonates with (TMS)3-SiH. The one-carbon ring expansion in the cyclopentanone series for the secondary alkyl radicals was studied over the temperature range 343-413 K by means of free-radical clock methodology and yielded the Arrhenius expression. The rate constant was 4.2 x 103 s-1 at room temperature and the reverse reaction (ring contraction) was found to be at least 10 times slower. Since the intermediacy of acyl radicals can be excluded, the reaction must occur via 3-membered cyclic intermediate radicals (or transition states).
- Chatgilialoglu, Chryssostomos,Ferreri, Carla,Lucarini, Marco,Venturini, Alessandro,Zavitsas, Andreas A.
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p. 376 - 387
(2007/10/03)
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- Inducibility of an Enone Reductase System in the Fungus Beauveria sulfurescens: Application in Enantioselective Organic Synthesis
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Microbiological reduction of α,β-unsaturated carbonyl compounds is studied.Inducibility of the enone reductase system of Beauveria sulfurescens is reported.The best inducer is shown to be cyclohex-2-en-1-one.An appropriate procedure using induced resting mycelium is developed to reduce substituted cyclohexenones that are shown to be unable to induce the reducing enzyme.Optically pure trans-(2R,6R)-(-)-2,6-dimethylcyclohexan-1-one and trans-(2R,6R)-(-)-2,6-dimethylcyclohexan-1-ol are obtained from (+/-)-2,6-dimethylcyclohex-2-en-1-one along with optically pure (6S)-(-)-2,6-dimethylcyclohex-2-en-1-one.
- Fauve, Annie,Renard, Michel F.,Veschambre, Henri
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p. 4893 - 4897
(2007/10/02)
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- KINETICALLY AND THERMODYNAMICALLY CONTROLLED SYNTHESIS OF 2,6-DISUBSTITUTED CYCLOHEXANONE SEMICARBAZONES. A MOLECULAR MECHANICS STUDY OF A1,3-STRAIN
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Reasonable values for Me-Me, H-Me and Me-H A1,3-strain have been evaluated by molecular mechanics calculations on differently substituted methylenecyclohexanes (5.46-6.75, 1.03 and 0.71 kcal/mol, respectively).The chair-to-chair inversion barri
- Castello, Assumpta,Jaime, Carlos,Marquet, Jorge,Moreno-Manas, Marcial
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p. 3791 - 3802
(2007/10/02)
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- ALKYLATION DIRECTE DE CETONES ET D'ALDEHYDES EN PRESENCE DE POTASSE SOLIDE EN SUSPENSION
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Dehydrated solid KOH, suspended in aprotic solvents, is used as a base for ketone and aldehyde alkylation.The best solvent as regards yields and selectivity is DME.The quantity of KOH depends on the carbonyl compound acidity.This method gives as good results as less convenient homogeneous conditions.
- Artaud, I.,Torossian, G.,Viout, P.
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p. 5031 - 5038
(2007/10/02)
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- Substituent Effects on the Stereochemistry of Substituted Cyclohexanone Dimethylhydrazone Alkylations. An X-ray Crystal Structure of Lithiated Cyclohexanone Dimethylhydrazone
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Substituent effects on the alkylations of the dimethylhydrazones of 2,4- and 2,6-disubstituted cyclohexanones are reported.High axial selectivities are observed in the alkylations of cyano-substituted metalated hydrazones, but not with alkoxycarbonyl-subs
- Collum, David B.,Kahne, Daniel,Gut, Sally A.,DePue, Randall T.,Mohamadi, Fariborz,et al.
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p. 4865 - 4869
(2007/10/02)
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