- 2,4,6-TRI-t-BUTYLPHENYLLITHIUM AS A BASE-----KINETIC DEPROTONATION OF BENZYL METHYL KETONE
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An extremely bulky lithium reagent, 2,4,6-tri-t-butylphenyllithium, was applied for deprotonation of benzyl methyl ketone to give the kinetic enol ether by "in situ" quenching with chlorotrimethylsilane as the major product indicating that the reagent serves as a hindered base.
- Yoshifuji, Masaaki,Nakamura, Tetsuo,Inamoto, Naoki
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- Regio- and stereoselective synthesis of silyl enol ethers using a new base electrogenerated from hexamethyldisilazane
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The hexamethyldisilazane magnesium salt, a new base readily electrogenerated in an undivided cell fitted with a sacrificial magnesium anode, using a normally equilibrating medium (DME/15% vol HMPA mixture), exhibited a surprising regioselectivity leading to the less highly substituted silyl enol ethers from unsymmetrical ketones. This regioselectivity was not temperature dependent, but was strongly dependent on the nature and proportions of the solvent/cosolvent mixture. Moreover, the reaction was different in pure NMP, and exclusively afforded, from 2-pentanone, the new silylated aldol (56% yield) which resulted from the condensation of the less highly substituted enolate with the ketone.
- Bonafoux, Dominique,Bordeau, Michel,Biran, Claude,Cazeau, Philippe,Dunogues, Jacques
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- Highly stereoselective oxazaborolidinium ion catalyzed synthesis of (Z)-silyl enol ethers from alkyl aryl ketones and trimethylsilyldiazomethane
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Highly stereoselective (Z)-silyl enol ethers were prepared from alkyl aryl ketones and trimethylsilyldiazomethane (TMSD) using an oxazaborolidinium ion catalyst. In addition, ring-expanded silyl enol ethers were successfully constructed from cyclic ketones. Their synthetic utilities were shown by sequential Mukaiyama aldol and [2 + 2]-cycloaddition reactions.
- Kang, Byung Chul,Shim, Su Yong,Ryu, Do Hyun
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p. 2077 - 2079
(2014/05/06)
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- Catalytic enantioselective amination of silyl enol ethers using chiral dirhodium(II) carboxylates: Asymmetric formal synthesis of (-)-metazocine
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(Chemical Equation Presented) Dirhodium(II) tetrakis[N- tetrafluorophthaloyl-(S)-tert-leucinate], Rh2(S-TFPTTL)4, is an exceptionally efficient catalyst for enantioselective aminations of silyl enol ethers derived from acyclic ketone
- Anada, Masahiro,Tanaka, Masahiko,Washio, Takuya,Yamawaki, Minoru,Abe, Takumi,Hashimoto, Shunichi
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p. 4559 - 4562
(2008/03/13)
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- A new method for the preparation of silyl enol ethers from carbonyl compounds and (trimenthylsily)diazomethane in a regiospecific and highly stereoselective manner
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The reaction of lithium (trimethylsilyl)diazomethane with aldehydes and ketones has been investigated, and it has been found that quenching at low temperature with MeOH followed by addition of Rh2(OAc)4 gave silyl enol ethers in high yields. Quenching with other electrophiles (e.g., deuterium, MeI) gave terminal and substituted silyl enol ethers with complete control over regio- and stereochemistry. The mechanism of this novel process has been mapped out through a combination of deuterium labeling, ReactIR, and isolation of reaction intermediates. Copyright
- Aggarwal, Varinder K.,Sheldon, Chris G.,Macdonald, Gregor J.,Martin, William P.
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p. 10300 - 10301
(2007/10/03)
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- Facile synthesis of silyl enol ethers by Mg-promoted coupling of aliphatic carbonyl compounds with trimethylsilyl chloride
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Treatment of aliphatic carbonyl compounds with trimethylsilyl chloride with Mg turning for Grignard reaction without any pre-treatment in N,N- dimethylformamide at room temperature brought about highly facile, effective and stereoselective coupling to give the corresponding silyl enol ethers in good yields.
- Ishino, Yoshio,Kita, Yoshio,Maekawa, Hirofumi,Ohno, Toshinobu,Yamasaki, Yasuhiro,Miyata, Toshiyuki,Nishiguchi, Ikuzo
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p. 1349 - 1352
(2007/10/03)
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- First synthesis of Se-(β-Oxoalkyl) selenothiophosphates
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General synthesis of a new class of Se-(β-oxoalkyl) selenothiophosphates based on selenothiophosphorylation of silyl enol ethers with thioxophosphoraneselenyl bromide is described.
- Dybowski,Kazimierczak,Skowronska
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p. 320 - 324
(2007/10/03)
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- Stereoselective electrochemical synthesis of silyl enol ethers using a sacrificial magnesium anode
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The 2-pyrrolidone magnesium salt electrogenerated in an undivided cell fitted with a sacrificial magnesium anode allowed the stereoselective synthesis of Z-silyl enol ethers upon deprotonation of enolizable ketones in the presence of a complexing agent. Keywords: Silyl enol ethers; Stereoselective synthesis; Electrogenerated bases; Sacrificial magnesium anode
- Bonafoux, Dominique,Bordeau, Michel,Biran, Claude,Dunogues, Jacques
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- Chemistry of oxaziridines. 14. Asymmetric oxidation of ketone enolates using enantiomerically pure (camphorylsulfonyl)oxaziridine
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The reagent-controlled asymmetric oxidation of tri- and tetrasubstituted ketone enolate anions 4 and 8 by enantiomerically pure (camphorylsulfonyl)oxaziridine 2 has been investigated. The stereoselectivities for oxidation of trisubstituted enolates 4a-d are good to excellent, 60-95% ee, while those for tetrasubstituted enolates 4e and 8 are lower; i.e., 21-30% ee. Isolated chemical yields for both types of enolate anions are good to excellent. The sodium enolate anions of 4a-d, which could be oxidized at -78°C, gave both higher yields and stereoselectivities than the corresponding lithium or zinc enolates, which required warming to higher temperatures for complete oxidation. The presence of HMPA generally had a deleterious effect on the stereoinduction. However, for oxidation of (E)- and (Z)-4d the highest ee's were observed in the presence of this additive. Investigation of the stereoselective trends reveals that the enolate substitution pattern and the enolate solution structure are the most important stereocontrol elements. The role that the enolate geometry has in the stereoinduction is less clear although Z enolates seem to exhibit higher stereoselectivities than the E enolates. The results obtained in this study have been formulated into a mechanistic rational involving an SN2-type substitution of the enolate anion on oxaziridine 2 via an "open" transition state.
- Davis, Franklin A.,Sheppard, Aurelia C.,Chen, Bang-Chi,Haque, M. Serajul
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p. 6679 - 6690
(2007/10/02)
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- SILICA SUPPORTED TETRABUTYLAMMONIUM FLUORIDE AS A CATALYST FOR THE SILYLATION OF CARBONYL ABD HYDROXY COMPOUNDS WITH ETHYLTRIMETHYLSILYLACETATE
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the use of silica supported tetrabutylammonium fluoride (TBAF-SiO2) as a non hygroscopic catalyst for silylating ketones and aldehydes with ethyltrimethylsilylacetate (ETSA) gives predominantly kinetic and Z silylenolethers at room temperature.TBAF-SiO2/ETSA is also useful in the silylation of alcohols.
- Gambacorta, Augusto,Turchetta, Stefano,Botta, Maurizio
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p. 2441 - 2448
(2007/10/02)
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- REGIO AND STEREOSELECTIVE PREPARATION OF ENOLATES FROM KETONES BY MEANS OF SODIUM BIS(TRIMETHYLSILYL)-AZIDE
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The deprotonation of some ketones by sodium bis(trimethylsilyl)-azide is regio and stereoselective.The results are different from those observed with LDA.
- Gaudemar, Marcel,Bellassoued, Moncef
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p. 2779 - 2782
(2007/10/02)
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- Syntheses with N-Trimethylsilylheteroarylium Salts: Reactions with Aldehydes, Ketones and Carboxylic Acids. Comparison of Reactivity with Analogous N-Acylheteroarylium Salts
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N-Trimethylsilylheteroarylium salts 2 can be characterized as efficient silylating reagents for carbonyl compounds (5 or 8) and carbonic acids 11, their reactivity is comparable to that of N-acylheteroarylium salts 1.In some cases (depending on the nature of the substrates), their silylating power can be stronger than the acylating power of comparable salts 1.This will be demonstrated in the case of enolizable examples of 5 and 8.
- Anders, Ernst,Stankowiak, Achim,Riemer, Roland
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p. 931 - 934
(2007/10/02)
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- A NEW PRACTICAL SYNTHESIS OF SILYL ENOL ETHERS. PART.I. FROM SIMPLE ALDEHYDES AND KETONES.
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A new, practical route to enoxysilanes is described from simple enolizable aldehydes or ketones, using the trimethylchlorosilane-sodium iodide-tertiary amine reagent in acetonitrile.From certain aldehydes, an onium intermediate has been isolated.A conformational study of this onium intermediate and a thermal unimolecular syn-elimination process may explain the stereoselectivity of the reaction.Such an interpretation can be extended to all the aldehydes and ketones considered.Steric factors related to the nature both of the cabonyl derivative and of the amine play a capital role for the regio- as well as for the stereo-control of the reaction.
- Cazeau, P.,Duboudin, F.,Moulines, F.,Babot, O.,Dunogues, J.
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p. 2075 - 2088
(2007/10/02)
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- On the Mechanism of the Thermal Conversion of Cyclopropenyl-Substituted Oxazolinones to Pyridines
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Thermolysis or photolysis of a sample of a 3-cyclopropenyl-substituted 2H-azirine produced 2-methyl-3,4,5,6-tetraphenylpyridine in high yield.The reaction can best be rationalized by a mechanism involving formation of a nitrile ylide intermediate followed by intramolecular dipolar cycloaddition to give an azabenzvalene, which subsequently rearranges to the pyridine.The thermal chemistry of a series of cyclopropenyl-substituted oxazolinones was also investigated.These oxazolinones undergo a thermally induced 1,3-dipolar cycloreversion reaction with elimination ofcarbon dioxide to generate a nitrile ylide intermediate adjacent to the cyclopropene ring.This dipole can be trapped when the thermolysis of the oxazolinone was carried out in the presence of a reactive dipolarophile.Heating a sample of 2-phenyl-4-methyl-4-(1-methyl-2,3-diphenyl-2-cyclopropen-1-yl)-Δ2-oxazolin-5-one at 150 deg C for 24 h afforded a mixture of 2,3-dimethyltriphenylpyridine (45percent), 2,4-dimethyltriphenylpyridine (20percent), and 2,5-dimethyltriphenylpyridine (35percent).The formation of these products is proposed to involve a stepwise cycloaddition of the initially generated nitrile ylide to produce a bicyclobutyl zwitterion which can either collapse to give an azabenzvalene or undergo rearrangement to a cyclobutenyl cation. This latter species closes to produce two different aza Dewar benzenes.Reorganization of the azabenzvalene and aza Dewar benzenes gives rise to the observed pyridines.Alternate mechanisms based on a concerted intramolecular cycloaddition reaction of the nitrile ylide do not account for the observed product ratios.
- Padwa, Albert,Cohen, Leslie A.,Gingrich, Henry L.
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p. 1065 - 1073
(2007/10/02)
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- Tris(dialkylamino)sulfonium Enolates. Synthesis, Structure, and Reactions
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A mixture of an enol trimethylsilyl ether and a fluoride salt exists in a dynamic equilibrium with an enolate species and fluorotrimethylsilane.Evacuation of an equimolar mixture of an enol trimethylsilyl ether of benzyl methyl ketone and tris(diethylamino)sulfonium (TAS) difluorotrimethylsiliconate produces fluorotrimethylsilane as the volatile fraction and the corresponding TAS enolate as air-sensitive crystals.The conductivity measurement and the 1H and 13C NMR analysis have substantiated the ionic nature of the TAS enolate in THF.The NMR chemical shifts are interpreted in terms of the electron distribution.The isolated TAS enolate undergoes O-acetylation with acetic anhydride and C-alkylation with methyl iodide exclusively.TAS enolate intermediates generated in situ from a series of enol silyl ethers and TAS difluorotrimethylsiliconate react with various active organic halides under mild conditions to give the regiospecific C-alkylation products.The in situ formed enolates react with aldehyde substrates to afford the β-trimethylsiloxy ketone adducts.In most cases, the reaction is kinetically controlled and the major products have erythro stereochemistry regardless of enolate configuration.This aldol reaction is postulated to proceed via an acyclic, extended transition state, in contrast to ordinary aldol reactions of Lewis acid coordinated enolates, which take place by way of six-membered chelate transition states.
- Noyori, R.,Nishida, I.,Sakata, J.
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p. 1598 - 1608
(2007/10/02)
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- SUR L'OBTENTION HAUTEMENT REGIO- ET STEREOSELECTIVED'ENOXYSILANES PAR ACTION DU BIS(TRIMETHYLSILYL)ACETAMIDE EN MILIEU HMPT SUR LESS DERIVES CARBONYLES ENOLISABLES
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The authors describe a new and general method for the preparation of enoxysilanes by silylation of enolizable aldehydes and ketones by use of bis(trimethylsilyl)acetamide in HMPT, in the presence of very small quantities of sodium metal(or another basic a
- Dedier, James,Gerval, Pierre,Frainnet, Emile
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p. 183 - 198
(2007/10/02)
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