- Synthesis of Cyclic Enones by Allyl-Palladium-Catalyzed α,β-Dehydrogenation
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The use of allyl-palladium catalysis for the one-step α,β-dehydrogenation of ketones via their zinc enolates is reported. The optimized protocol utilizes commercially available Zn(TMP)2 as base and diethyl allyl phosphate as oxidant. Notably, this transformation operates under salt-free conditions and tolerates a diverse scope of cycloalkanones.
- Huang, David,Zhao, Yizhou,Newhouse, Timothy R.
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supporting information
p. 684 - 687
(2018/02/09)
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- Allyl-Palladium-Catalyzed Ketone Dehydrogenation Enables Telescoping with Enone α,β-Vicinal Difunctionalization
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The telescoping of allyl-palladium catalyzed ketone dehydrogenation with organocuprate conjugate addition chemistry allows for the introduction of aryl, heteroaryl, vinyl, acyl, methyl, and other functionalized alkyl groups chemoselectively to a wide variety of unactivated ketone compounds via their enone counterparts. The compatibility of the dehydrogenation conditions additionally allows for efficient trapping of the intermediate enolate with various electrophiles. The utility of this approach is demonstrated by comparison to several previously reported multistep sequences.
- Chen, Yifeng,Huang, David,Zhao, Yizhou,Newhouse, Timothy R.
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supporting information
p. 8258 - 8262
(2017/06/30)
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- Hydrolytic enantioselective protonation of cyclic dienyl esters and a β-diketone with chiral phase-transfer catalysts
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Hydrolytic enantioselective protonation of dienyl esters and a β-diketone catalyzed by phase-transfer catalysts are described. The latter reaction is the first example of an enantio-convergent retro-Claisen condensation. Corresponding various optically active α,β-unsaturated ketones having tertiary chiral centers adjacent to carbonyl groups were obtained in good to excellent yields and enantiomeric ratios (83-99%, up to 97.5:2.5 er).
- Yamamoto, Eiji,Gokuden, Daichi,Nagai, Ayano,Kamachi, Takashi,Yoshizawa, Kazunari,Hamasaki, Akiyuki,Ishida, Tamao,Tokunaga, Makoto
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supporting information
p. 6178 - 6181
(2013/02/25)
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- 3-Alkyl-p-menthan-3-ol derivatives: synthesis and evaluation of their physiological cooling activity
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Different 3-alkyl-p-methan-3-ol derivatives provide a strong physiological cooling effect with potential application as food and cosmetic additives. In order to investigate the influence of the chemical structure on the cooling sensation, the stereoselective syntheses of 29 different 3-alkyl-p-methan-3-ol derivatives were accomplished. All the compounds obtained are odorless and were evaluated by taste, considering two sensations: a cooling effect and bitterness. The results of this structure-activity relationship study highlight that compounds with a (1R,4S)-configuration are the isomers with the more intense cooling effect and lower bitterness. In addition, the structure of the 3-alkyl chain affected the latter properties. Increasing the chain length over two carbon atoms does not change the cooling power, but enhances the bitterness with the additional feature that the branched isomers are considerably more bitter than the linear ones. Overall, the 3-alkyl-p-menthan-3-ol isomers with the best quality in terms of high cooling power and low bitterness are (1R,4S)-3-(hydroxymethyl)-p-menthan-3-ol diastereoisomers (-)-38 and (-)-42.
- Fuganti, Claudio,Joulain, Daniel,Maggioni, Francesco,Malpezzi, Luciana,Serra, Stefano,Vecchione, Andrea
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body text
p. 2425 - 2437
(2009/04/06)
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- Highly enantio- and s-trans C=C bond selective catalytic hydrogenation of cyclic enones: Alternative synthesis of (-)-menthol
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A highly enantioselective catalytic hydrogenation of cyclic enones was achieved by using the combination of a cationic Rh1 complex, (S)-5,5′-bis{di(3,5-di-tert-butyl-4-methoxyphenylphosphino)}-4, 4′-bi-1,3-benzodioxole (DTBM-SEGPHOS), and (CH2CH 2PPh3Br)2. The presence of an s-cis C=C bond isopropylidene moiety on the cyclic enone influenced the enantioselectivity of the hydrogenation. Thus, the hydrogenation of 3-alkyl-6-isopropylidene-2- cyclohexen-1-one, which contains both s-cis and s-trans enones, proceeded in excellent enantioselectivity (up to 98% ee). To obtain high enantio- and s-trans selectivities, the addition of a halogen source to the cationic Rh complex was the essential step. With the key step of the s-trans selective asymmetric hydrogenation of piperitenone, we demonstrated a new synthetic method for optically pure (-)-menthol via three atom-economical hydrogenations. Moreover, we found that the complete s-trans and s-cis C=C bond selective reactions were also realized by the proper choice of both the chiral ligands and halides.
- Ohshima, Takashi,Tadaoka, Hiroshi,Hori, Kiyoto,Sayo, Noboru,Mashima, Kazushi
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scheme or table
p. 2060 - 2066
(2009/04/07)
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- α,β-Unsaturated and cyclopropyl acyl radicals, and their ketene alkyl radical equivalents. Ring synthesis and tandem cyclisation reactions
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Treatment of the α,β-unsaturated selenyl esters 12 and 14 with Bu3SnH-AIBN produces the corresponding 2-cyclohexenones 13 and 15 respectively via presumed α-ketene alkyl radical intermediates, viz. 10. By contrast, the 2,7-diene esters 34 and 39 undergo tandem radical cyclisations producing diquinanes, e.g. 38 (76%), and the corresponding allene-substituted α,β-unsaturated selenyl ester 48 gives the cyclooctadienone 56 on treatment with Bu3SnH-AIBN in refluxing benzene. The selenyl ester 19 derived from chrysanthemic acid produces a mixture of the γ,δ- unsaturated aldehyde 22 and the corresponding dimer 25a on treatment with Bu3SnH-AIBN. Furthermore, in the presence of methanol the only product from this reaction was the bis(methyl ester) dimer 25b, thereby lending further credence to the involvement of ketene alkyl radical intermediates in these reactions, and in the aforementioned reactions involving 2,6- and 2,7-diene selenyl esters. Treatment of the cyclopropane selenyl esters 59 and 61, containing keto- and oxy-group functionality in their side-chains, with Bu3SnH-AIBN led to excellent syntheses of the enol lactone 66 (76%) and the trans-fused bicyclo[6.1.0]nonane 67 (80-95%) respectively.
- Hayes, Christopher J.,Herbert, Nicola M. A.,Harrington-Frost, Nicole M.,Pattenden, Gerald
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p. 316 - 327
(2007/10/03)
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- Catalytic cross-coupling of alkylzinc halides with α-chloroketones
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The cross-coupling of alkylzinc halides with α-chloroketones catalyzed by Cu(acac)2 is described. Using this method, primary and secondary alkyl groups are introduced adjacent to a ketone carbonyl under mild reaction conditions and in good yield. Cyclic, acyclic, aromatic, and aliphatic α-chloroketones are suitable substrates. Optically active α-chloroketones are converted to optically active products. The reaction was found to proceed stereospecifically with inversion of stereochemistry. The reaction is proposed to occur by direct substitution of the chloride with the alkyl group of an organocopper, -magnesium, or -zinc species. Copyright
- Malosh, Chrysa F.,Ready, Joseph M.
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p. 10240 - 10241
(2007/10/03)
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- Lipase-catalyzed resolution of p-menthan-3-ols monoterpenes: Preparation of the enantiomer-enriched forms of menthol, isopulegol, trans- and cis-piperitol, and cis-isopiperitenol
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A study on the enzymic resolution of the most common p-menthan-3-ol monoterpene isomers is described. Enantioenriched alcohols 1, 5, 10, 11 and 12 are obtained by means of the lipase-mediated kinetic acetylation of the corresponding racemic materials. The stereochemical aspects of the enzymic process have been investigated. We found that the structural features of the starting p-menthan-3-ol as well as the kind of lipase used, impacted strongly on the enantioselectivity of the resolution. The potentialities of this approach for preparative purposes are discussed.
- Serra, Stefano,Brenna, Elisabetta,Fuganti, Claudio,Maggioni, Francesco
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p. 3313 - 3319
(2007/10/03)
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- Method for producing 1-menthol
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Provided is a method for the production of 1-menthol, which comprises hydrogenation of piperitenone with a transition metal complex of a specified optically active phosphine to produce pulegone, hydrogenation of the obtained pulegone with a ruthenium-phosphine-amine complex in the presence of base to obtain pulegol, and further hydrogenation of the pulegol with a transition metal catalyst.
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- α′-hydroxy-α,β-unsaturated tosylhydrazones: Preparation and use as intermediates for carbonyl and enone transpositions
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Regiospecifically generated α,β-unsaturated tosylhydrazones dianions are treated with molecular oxygen, yielding α′-hydroxy-α,β-unsaturated tosylhydrazones, versatile intermediates for organic synthesis. They proved to be useful for 1,2-carbonyl and 1,2-enone transpositions, and also permitted the preparation of α′-hydroxy enones in very high yields.
- Baptistella, Lucia H. B.,Aleixo, Adriana M.
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p. 2937 - 2950
(2007/10/03)
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- Catalytic and stoichiometric Lewis acid participation in aldehyde ene cyclisations
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Racemic 2-isopropyl-2-methylhex-5-enal has been synthesised in order to probe ene cyclisations leading to menthol analogues. The objective was first to discover catalytic conditions for preferential cyclisation to the menthol rather than the neomenthol series and then to develop (dynamic) kinetic resolution procedures which afforded a single enantiomer of product. It was found that catalytic quantities of both Me2AlCl and a bulky methyl-aluminium bis(phenoxide) reagent gave products attributed to a Meerwein-Pondorff-Verley reaction. In this the aldehyde is reduced to a primary alcohol and the ene product oxidised to the corresponding α,β-unsaturated ketone. By contrast, a related bulky chloroaluminium reagent catalysed the ene cyclisation cleanly, but preferentially to the undesired neomenthyl stereoisomer.
- Braddock, D. Christopher,Brown, John M.
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p. 741 - 756
(2007/10/03)
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- Desilylative oxidation of alkyl trimethylsilyl ethers with pyridinium fluorochromate
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Direct conversion of alkyl trimethylsilyl ethers to carbonyl compounds is accomplished using PFC in dichloromethane at room temperature. For a similar oxidation of t-butyldimethylsilyl ethers the PCC-n-Bu4NF combination may be employed.
- Ho, Tse-Lok,Jana, Gour Hari
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p. 639 - 640
(2007/10/03)
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- α-Ketene alkyl and α,β-unsaturated acyl radical intermediates in ring constructions
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Treatment of the E-α,β-unsaturated selenyl esters and 1 and 3a with Bu3SnH-AIBN produces the corresponding cyclohexones 2 and 7/8 respectively via presumed α-ketene alkyl radical intermediates. In a similar manner the cyclopropyl ester 9 leads to a mixture of 12 and 13, and the 2,7-diene selenyl ester 15 undergoes a novel bi-cyclisation producing the diquinane 17 in 76% yield.
- Hayes, Christopher J.,Pattenden, Gerald
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p. 271 - 274
(2007/10/02)
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- The Lewis acid-catalyzed intramolecular asymmetric ene reaction using a chiral α-cyanovinylic sulfoxide as an enophile
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A chiral α-cyanovinylic sulfoxide served as an efficient chiral enophile in a Lewis acid-catalyzed intramolecular ene reaction. Use of diethylaluminum chloride as a catalyst provided extremely high stereoselectivity in the ene reaction. The stereochemistry of the ene reaction products were determined by chemical correlation and the NMR spectral analysis. A mechanistic pathway for the asymmetric induction is presented on the basis of the stereochemical results obtained.
- Hiroi, Kunio,Umemura, Masayuki
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p. 1831 - 1840
(2007/10/02)
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- Lewis Acid-catalyzed Intramolecular Asymmetric Ene Reactions of Chiral Vinyl Sulfoxides
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A chiral α-cyanovinyl sulfoxide served as an efficient chiral enophile in a Lewis acid-catalyzed intramolecular ene reaction.Use of diethylaluminum chloride as a catalyst provided extremely high stereoselectivity in this ene reaction.Based on the stereochemical results obtained, a mechanistic pathway for this asymmetric induction is presented.
- Hiroi, Kunio,Umemura, Masayuki
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p. 3343 - 3346
(2007/10/02)
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- IMPROVED METHOD OF OBTAINING PIPERITONE
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A new convenient variant of the reduction of thymol methyl ether by lithium and isopropanol in the presence of ethylenediamine at 80-85 deg C and a molar equivalent ratio of ether to alcohol to amine to metal of 1:(8-12):(2.5-3):(4-6) has been developed.The proposed method permits the yield of piperitone to be doubled in comparison with known methods.
- Bazyl'chik, V. V.,Overchuk, T. N.
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p. 292 - 295
(2007/10/02)
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- CATALYTIC ASYMMETRIC SYNTHESES. Part III. Asymmetric Hydrogenation of Piperitenone Catalysed by Chiral Ruthenium Hydrides: An Example of a Catalytic Kinetic Resolution.
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Piperitenone has been hydrogenated in the presence of chiral ruthenium catalysts to give piperitone, menthone and isomenthone.Starting from piperitone (42 percent e.e.) excellent selectivity (80 percent e.e.) was obtained with menthone.The mechanism of the reaction, a double asymmetric synthesis, is discussed with respect to kinetic resolution of piperitone as well as the effect of the chiral center in the substrate on the catalytic asymmetric induction.
- Le Maux, Paul,Massonneau, Viviane,Simonneaux, Gerard
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p. 1409 - 1412
(2007/10/02)
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- Acid-catalyzed Rearrangements of Linalool Oxide
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Reaction of linalool oxide (1) with acids leads to a variety of dehydration products which are shown to be aliphatic dienones and /or monocyclic enones.A mechanism is proposed to account for the generation of all these compounds.
- Ho, Tse-Lok,Liu, Shing-Hou
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p. 761 - 769
(2007/10/02)
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- ZUR REGIOSELEKTIVITAET BEIM ALDOL-RINGSCHLUSS
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According to the proper choice of reaction conditions, a regioselective ring closure of the 1,5-diketones I is achieved, either to II or III.This directed aldolisation was successfully applied to a short synthesis of the monoterpenoid piperitone.
- Kreiser, Wolfgang,Below, Peter
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p. 429 - 432
(2007/10/02)
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- THE ABSOLUTE CONFIGURATION OF THE DICIPIENE DITERPENES
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The absolute configuration of the dicipiene diterpenes has been determined by degradation to 4R-4-(2-methoxy-4-methylphenyl)-pentanoic acid.Photolysis of 1,18-diacetoxy-13-oxodecipi-14-ene proceeds through a novel photochemical reaction, formally a cycloreversion, to generate a key intermediate for the degradation.
- Croft, K. D.,Ghisalberti, E. L.,Jefferies, P. R.,Stuart, A. D.
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p. 383 - 387
(2007/10/02)
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- Sensitized Photooxygenation of Silyl Enol Ethers of Cyclic Ketones
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α,β-Unsaturated and α-hydroxy ketones are accessible in prototropic ene-reactions with singlet oxygen by sensitized photooxygenation of cyclic silyl enol ethers and subsequent reduction and solvolysis.In a competing silatropic ene-reaction α-silyloxyketones are formed.Formation of different products depends on ring size, configuration and substitution.At C-6 chirally substituted 2-cyclohexenones are synthesized for the first time by sensitized photooxygenation of chiral silyl enol ethers of optically active starting ketones.
- Friedrich, Edgar,Lutz, Werner
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p. 1245 - 1263
(2007/10/02)
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