- Reaction of acylsilanes with α-sulfinyl carbanions: Regioselective synthesis of silyl enol ethers
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The reaction of acylsilanes with α-sulfinyl carbanions such as α-lithioalkyl sulfoxide is described. The reaction proceeds to give silyl enol ethers preferentially through the initial formation of the α-silyl alkoxide intermediates. In particular, the products derived from enolizable acylsilanes were the regio-defined silyl enol ethers that cannot be obtained by usual enolization of the corresponding unsymmetrical ketones with base.
- Honda, Mitsunori,Nakajima, Tadashi,Okada, Maiko,Yamaguchi, Keita,Suda, Mitsuhiro,Kunimoto, Ko-Ki,Segi, Masahito
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experimental part
p. 3740 - 3742
(2011/08/06)
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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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- Reaction of acylsilanes with sulfur ylides. Selective formation of silyl enol ethers or β-ketosilanes
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The reaction of acylsilanes with sulfur ylides in THF results in the formation of the corresponding silyl enol ethers or β-ketosilanes. The relative ratio of these products varies with the ylide conditions and the stability of ylide used. It is noteworthy that silyl enol ethers were formed under the salt-free ylide conditions, and that β-ketosilanes were yielded in the presence of soluble inorganic salts in THF, selectively. The formation of both products would be interpreted in terms of the anionotropic and cationotropic rearrangements of silyl group in the reaction intermediate.
- Nakajima, Tadashi,Segi, Masahito,Sugimoto, Fumitosi,Hioki, Reiko,Yokota, Seiko,Miyashita, Kiyoshi
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p. 8343 - 8358
(2007/10/02)
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- Enolate Ions, II. - Convenient Synthesis of 3,4-Dihydro-2,4-dioxo-2H-pyrans and 2-Pyrones. - Enolate Ions as Synthetic Equivalents of 1,3-Dianions. - Crystal and Molecular Structure of Ethyl 6-Ethoxy-3,4-dihydro-3,3-dimethyl-2,4-dioxo-2H-pyran-5-carboxyla
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Reaction of dimethylmalonyl chloride (6a) or cyclic 1,1-dicarbonyl dichlorides 6b-d with two equivalents of lithium enolates 7, 22, and silyl enol ethers 8, respectively, yields 3,4-dihydro-2,4-dioxo-2H-pyrans 10, 24, or spiro compounds 11-13, 25-27.The s
- Saalfrank, Rolf W.,Guendel, Juergen,Rossmann, Guenther,Hanek, Martin,Rost, Walter,et al.
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p. 1175 - 1183
(2007/10/02)
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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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- 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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- 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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p. 6325 - 6328
(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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- REGIOSELECTIVE PREPARATION OF KINETIC TRIMETHYLSILYL ENOL ETHERS FROM β-KETO SILANES
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Kinetic trimethylsilyl enol ethers were prepared regioselectively by the two-step method, i.e., trimethylsilyl triflate catalyzed rearrangement of β-keto silanes which were prepared from trimethylsilylmethylcopper and acid chlorides.
- Yamamoto, Yohsuke,Ohdoi, Keisuke,Nakatani, Masayuki,Akiba, Kin-ya
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p. 1967 - 1968
(2007/10/02)
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- HIGHLY SELECTIVE, KINETICALLY CONTROLLED ENOLATE FORMATION USING LITHIUM DIALKYLAMIDES IN THE PRESENCE OF TRIMETHYLCHLOROSILANE
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The deprotonation of ketones and esters with lithium dialkylamides in the presence of trimethylchlorosilane leads to enhanced selectivity for the kinetically generated enolate.Lithium t-octyl-t-butylamide is shown to be superior to lithium diisopropylamid
- Corey, E. J.,Gross, Andrew W.
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p. 495 - 498
(2007/10/02)
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- Reactions of Trialkylsilyl Trifluoromethanesulfonates, I. - Synthesis of Trialkylsilyl Enol Ethers
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The reactions of the ketones 2,2-bromoketones 6, α,β-unsaturated ketones 8, 1,2-diketones, and aliphatic aldehydes 20 with trialkylsilyl triflates 1 in the presence of triethylamine (4) at room temperature yield the silyl enol ethers 3, 7, 9, 11, and 21.The silylation of the unsymmetrical ketones 12 with 1a/4 runs regioselectively in the thermodynamical sense using 1a/12 in excess and yields the enol ethers 13t.The course of this reaction is discussed briefly.
- Emde, Herbert,Goetz, Andreas,Hofmann, Karin,Simchen, Gerhard
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p. 1643 - 1657
(2007/10/02)
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- Alkylation and arylation of 2-trimethylsiloxyallyl halides. A new regiospecific route to silyl enol ethers
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Alkylation and arylation of 2-trimethylsiloxyallyl halides with lithium dialkyl- and diarylcuprate, respectively, gave silyl enol ethers in a regiospecific manner.
- Sakurai, Hideki,Shirahata, Akihiko,Araki, Yoshitaka,Hosomi, Akira
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p. 2325 - 2328
(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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