- Enolate-Based Regioselective Anti-Beckmann C-C Bond Cleavage of Ketones
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The Baeyer-Villiger or Beckmann rearrangements are established methods for the cleavage of ketone derivatives under acidic conditions, proceeding for unsymmetrical precursors selectively at the more substituted site. However, the fragmentation regioselectivity cannot be switched and fragmentation at the less-substituted terminus is so far not possible. We report here that the reaction of ketone enolates with commercial alkyl nitrites provides a direct and regioselective way of fragmenting ketones into esters and oximes or ω-hydroxyimino esters, respectively. A comprehensive study of the scope of this reaction with respect to ketone classes and alkyl nitrites is presented. Control over the site of cleavage is gained through regioselective enolate formation by various bases. Oxidation of kinetic enolates of unsymmetrical ketones leads to the otherwise unavailable "anti-Beckmann"cleavage at the less-substituted side chain, while cleavage of thermodynamic enolates of the same ketones represents an alternative to the Baeyer-Villiger oxidation or the Beckmann rearrangement under basic conditions. The method is suited for the transformation of natural products and enables access to orthogonally reactive dicarbonyl compounds.
- Jahn, Ullrich,Ma?ek, Tomá?
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p. 11608 - 11632
(2021/09/02)
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- METHOD FOR PRODUCING SILYLENOL ETHERS
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The present invention provides a method for producing a silyl enol ether compound, which is convenient, has highly broad utility and places a low environmental load (less waste). The present invention relates to a method for producing silyl enol ether compound (3), including reacting ketone or aldehyde compound (1) with allylsilane compound (2) in the presence of a base and 0.00001 to 0.5 equivalents of an acid catalyst relative to ketone or aldehyde compound (1), wherein R1 is a hydrogen atom, an alkyl group, an aryl group or the like; R2 and R3 are each a hydrogen atom, a halogen atom, an alkyl group, an aryl group or the like; R1 and R3, R1 and R2, or R2 and R3 optionally form a ring, together with the carbon atom(s) bonded thereto; R4 , R5 and R6 are each a hydrogen atom, an alkyl group or the like; two of R4, R5 and R6 optionally form a ring; R7, R8, R9, R10 and R11 are each a hydrogen atom, an alkyl group or the like; two of R7, R8, R9, R10 and R11 optionally form a ring.
- -
-
Paragraph 0098; 0103
(2013/03/26)
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- Facile isomerization of silyl enol ethers catalyzed by triflic imide and its application to one-pot isomerization-(2 + 2) cycloaddition
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A triflic imide (Tf2NH) catalyzed isomerization of kinetically favourable silyl enol ethers into thermodynamically stable ones was developed. We also demonstrated a one-pot catalytic reaction consisting of (2 + 2) cycloaddition and isomerization. In the reaction sequence, Tf2NH catalyzes both of the reactions.
- Inanaga, Kazato,Ogawa, Yu,Nagamoto, Yuuki,Daigaku, Akihiro,Tokuyama, Hidetoshi,Takemoto, Yoshiji,Takasu, Kiyosei
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supporting information; experimental part
p. 658 - 661
(2012/06/01)
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- Palladium-catalyzed cross-coupling of cyclopropanols with aryl halides under mild conditions
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Intra- and intermolecular palladium-catalyzed cross-coupling of cyclopropanols with aryl halides can be achieved in good yields under mild conditions.
- Rosa, David,Orellana, Arturo
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supporting information; experimental part
p. 110 - 113
(2011/03/22)
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- Enantioselective decarboxylative alkylation reactions: Catalyst development, substrate scope, and mechanistic studies
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α-Quaternary ketones are accessed through novel enantioselective alkylations of allyl and propargyl electrophiles by unstabilized prochiral enolate nucleophiles in the presence of palladium complexes with various phosphinooxazoline (PHOX) ligands. Excellent yields and high enantiomeric excesses are obtained from three classes of enolate precursor: enol carbonates, enol silanes, and racemic β-ketoesters. Each of these substrate classes functions with nearly identical efficiency in terms of yield and enantioselectivity. Catalyst discovery and development, the optimization of reaction conditions, the exploration of reaction scope, and applications in target-directed synthesis are reported. Experimental observations suggest that these alkylation reactions occur through an unusual inner-sphere mechanism involving binding of the prochiral enolate nucleophile directly to the palladium center. Sly as a PHOX: The development of an enantioselective decarboxylative palladium-catalyzed allylic alkylation reaction, utilizing phosphinooxazoline ligands, is described. The catalyst is applied to a range of allyl enol carbonate, silyl enol ether, and allyl β-ketoester substrates to provide alkylated ketone products in excellent yield and good ee (see scheme). The utility of these products is demonstrated by their use in several asymmetric syntheses. Mechanistic studies are reported suggesting an unusual inner-sphere mechanism. Copyright
- Behenna, Douglas C.,Mohr, Justin T.,Sherden, Nathaniel H.,Marinescu, Smaranda C.,Harned, Andrew M.,Tani, Kousuke,Seto, Masaki,Ma, Sandy,Novak, Zoltan,Krout, Michael R.,McFadden, Ryan M.,Roizen, Jennifer L.,Enquist Jr., John A.,White, David E.,Levine, Samantha R.,Petrova, Krastina V.,Iwashita, Akihiko,Virgil, Scott C.,Stoltz, Brian M.
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supporting information; experimental part
p. 14199 - 14223
(2012/02/01)
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- Efficient control for the cationic platinum(II)-catalyzed concise synthesis of two types of fused carbocycles with angular oxygen functionality
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Double trouble: An efficient method for the preparation of two types of synthetically useful bicyclo[5.4.0]undecanes with an angular oxygen functionality was realized starting from easily available substrates; this method was based on the [3+2] cycloaddit
- Kusama, Hiroyuki,Watanabe, Eiichi,Ishida, Kento,Iwasawa, Nobuharu
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experimental part
p. 2273 - 2277
(2012/06/30)
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- Mechanistic studies on α-trifluoromethylation of ketones via silyl enol ethers and its application to other carbonyl compounds
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(Chemical Equation Presented) Synthesis of α-CF3 carbonyl compounds has been recognized to be difficult up to now because the polarization of CF3δ--Iδ+ is opposite to that of CH3δ+-Iδ-, and this makes it difficult to introduce CF3+ unit to enolates. We recently reported an effective R-trifluoromethylation of ketones by using Et 2Zn with Rh catalyst, but the mechanism has not fully been cleared. Now, we carried out the detailed mechanistic studies and found the involvement of a highly reactive alkylrhodium complex which derived from Et2Zn and RhCl(PPh3)3 in this α-trifluoromethylation. Furthermore, this α-trifluoromethylation was applied to other types of carbonyl compounds in good yields.
- Sato, Kazuyuki,Yuki, Takashi,Yamaguchi, Ryoji,Hamano, Tetsuya,Tarui, Atsushi,Omote, Masaaki,Kumadaki, Itsumaro,Ando, Akira
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supporting information; experimental part
p. 3815 - 3819
(2009/10/01)
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- CuBr-catalyzed reaction of N,N-dimethylanilines and silyl enol ethers: An alternative route to β-arylamino ketones
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Image Presented A wide range of silyl enol ethers undergo the reactions with N,N-dimethylanilines in the presence of transition metal catalysts under mild conditions to give β-arylamino ketones. In the cases of silyl enol ethers derived from unsymmetrical ketones, regiospecific addition of carbonyl compounds was obtained at the olefinic position of silyl enol ether.
- Huang, Lehao,Zhang, Xunbin,Zhang, Yuhong
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supporting information; experimental part
p. 3730 - 3733
(2011/03/18)
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- Asymmetric synthetic access to the hetisine alkaloids: Total synthesis of (+)-nominine
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A dual cycloaddition strategy for the synthesis of the hetisine alkaloids has been developed, illustrated by a concise asymmetric total synthesis of (+)-nominine (7). The approach relies on an early-stage intramolecular 1,3-dipolar cyclo-addition of a 4-o
- Peese, Kevin M.,Gin, David Y.
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supporting information; experimental part
p. 1654 - 1665
(2009/04/04)
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- Chiral and achiral lithium amides having a fluorous ponytail: Preparation and evaluation as a recycling reagent for lithium enolate generation
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Diisopropylamine derivatives bearing a perfluoroalkyl chain were prepared and converted to the corresponding lithium amides by treatment with n-butyllithium. The fluorous lithium amides reacted with ketones to efficiently produce lithium enolates. Asymmetric deprotonation of prochiral ketones was also studied using lithium amides derived from chiral fluorous amines, which gave optical yields comparable with the parent nonfluorous chiral lithium amides. These reusable fluorous amines can be easily recovered by liquid-liquid extraction or chromatographic separation. Georg Thieme Verlag Stuttgart.
- Matsubara, Hiroshi,Maeda, Louis,Sugiyama, Hiroyuki,Ryu, Ilhyong
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p. 2901 - 2912
(2008/03/13)
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- New method for the synthesis of 2-aza-1,3-butadienes
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2-Aza-1,3-butadienes have been synthesized from carbonyl compounds and 1,1,1,3,3,3-hexamethyl-disilazane in the presence of cobalt-containing catalysts. The best yields (up to 95%) were achieved in the case of aldehydes branched in the α-position and 2-methylcyclohexanone. In the case of two α,β-unsaturated ketones, pyridine derivatives were found as the main products. Copyright Taylor & Francis Group, LLC.
- Sisak, Attila
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p. 3693 - 3702
(2007/10/03)
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- The enantioselective Tsuji allylation
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The first catalytic enantioselective examples of the Tsuji allylation using enol carbonates and enol silanes are described. The products possess a quaternary stereogenic center and are useful building blocks for synthetic chemistry. Copyright
- Behenna, Douglas C.,Stoltz, Brian M.
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p. 15044 - 15045
(2007/10/03)
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- Silazanes/catalytic bases: Mild, powerful and chemoselective agents for the preparation of enol silyl ethers from ketones and aldehydes
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We have developed an efficient method for the preparation of enol silyl ethers using novel agents, silazanes together with NaH or DBU catalyst, wherein TMS and TBDMS groups were smoothly and chemoselectively introduced into ketones and aldehydes under mil
- Tanabe, Yoo,Misaki, Tomonori,Kurihara, Minoru,Iida, Akira,Nishii, Yoshinori
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p. 1628 - 1629
(2007/10/03)
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- Preparation of silyl enol ethers using (bistrimethylsilyl)acetamide in ionic liquids
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(matrix presented) Ionic liquids have been used for the preparation of silyl enol ethers from aldehydes and ketones with (bistrimethylsilyl)acetamide (BSA) in good yields.
- Smietana, Michael,Mioskowski, Charles
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p. 1037 - 1039
(2007/10/03)
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- Preparation of 2,3-epoxycycloalkanones from bicyclo[n.1.0]Alkan-1-ols
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Copper- or iron-catalyzed oxidative rearrangement of bicyclo[n.1.0]alkan-1-ols yields 3-hydroperoxycycloalkanones and/or bicyclic peroxyhemiketals, which are transformed into 2,3-epoxycycloalkanones by treatment with a base.
- Barnier,Morisson,Blanco
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p. 349 - 357
(2007/10/03)
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- Enantioselective protonation of silyl enol ethers and ketene disilyl acetals with Lewis acid-assisted chiral Bronsted acids: Reaction scope and mechanistic insights
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Enantioselective protonation is a potent and efficient way to construct chiral carbons. Here we report details of the reaction using Lewis acid-assisted chiral Bronsted acids (chiral LBAs). The 1:1 coordinate complex of tin tetrachloride and optically active binaphthol ((R)- or (S)-BINOL) can directly protonate various silyl enol ethers and ketene disilyl acetals to give the corresponding α-aryl ketones and α-arylcarboxylic acids, respectively, with high enantiomeric excesses (up to 98% ee). A catalytic version of enantioselective protonation has also been achieved using stoichiometric amounts of 2,6-dimethylphenol and catalytic amounts of monomethyl ether of optically active BINOL in the presence of tin tetrachloride. This protonation is also effective for producing α-halocarbonyl compounds (up to 91% ee). DFT calculations on the B3LYP/LANL2DZ level show that the conformational structure of the chiral LBA and the orientation of activated proton on (R)-BINOLs are important for understanding the absolute stereochemistry of the products.
- Nakamura, Shingo,Kaneeda, Masanobu,Ishihara, Kazuaki,Yamamoto, Hisashi
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p. 8120 - 8130
(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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- Effect of cyclohexenonic long chain fatty alcohols on neurite outgrowth. Study on structure-activity relationship
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Four series of long chain fatty alcohols bearing a cyclohexenone moiety in addition to a ω-alkanol side chain were synthesized using 'Umpolung' reactivity strategy. Their effect on neurite outgrowth was evaluated by means of fetal rat neurons in culture. The length of the ω-hydroxy side chain is a crucial factor for biological activity.
- Girlanda-Junges, Celine,Keyling-Bilger, Florence,Schmitt, Gaby,Luu, Bang
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p. 7735 - 7748
(2007/10/03)
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- Easy preparation of enoxysilanes from aldehydes and ketones catalyzed by samarium diiodide
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Ketones and α-substituted aldehydes are converted to trimethylsilyl enol ethers by reaction with the trimethylsilyl ketene acetal of methyl isobutyrate in dichloromethane in presence of a catalytic amount of samarium diiodide.
- Hydrio, Jerome,Van De Weghe, Pierre,Collin, Jacqueline
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- A practical method for the preparation of trimethylsilyl enol ethers
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In the mixed system of chlorotrimethylsilane/triethyl amine/N,N-dimethylformamide/potassium iodide/petroleum ether, aldehydes or ketones are silylated to silyl enol ethers at room temperature. The N,N-dimethylformamide/potassium iodide layer can be used as circulating liquor for many times. The yields are high.
- Lin, Ji-Mao,Liu, Ben-Sheng
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p. 739 - 749
(2007/10/03)
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- X-ray crystallographic studies and comparative reactivity studies of a sodium diisopropylamide (NDA) complex and related hindered amides
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Two related sodium amide complexes derived from secondary amines with bulky organic substituents have been synthesised and crystallographically characterised. Both [(iPr)2NNa(TMEDA)]2 and [Cy(iPr)NNa(TMEDA)]2 adopt dimeric crystal structures with a central, planar (nitrogen-metal)2 azametallocycle, a now familiar feature in both lithium amide and sodium amide chemistry. TMEDA ligands chelate in their usual bidentate manner making the Na+ cations four-coordinate with a distorted tetrahedral geometry. In the latter complex, the amido substituents are disposed in a trans conformation with respect to the (NNa)2 ring plane. The deprotonating ability of the former complex has been tested against that of the parent amide [(iPr)2NNa]∞ and the lithium congener [(iPr)2NLi]∞ (LDA) in a series of simple organic reactions: selective enolate formation from 2-octanone and 2-methylcyclohexanone; synthesis of diphenylacetic acid via diphenylmethane. In general, the performance of the sodium reagents compares favourably with that of the lithium reagent.
- Andrews, Philip C.,Barnett, Nicholas D.R.,Mulvey, Robert E.,Clegg, William,O'Neil, Paul A.,Barr, Donald,Cowton, Lucy,Dawson, Andrea J.,Wakefield, Basil J.
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- α-nitration of ketones via enol silyl ethers. Radical cations as reactive intermediates in thermal and photochemical processes
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Highly colored (red) solutions of various enol silyl ethers and tetranitromethane (TNM) are readily bleached to afford good yields of α-nitro ketones in the dark at room temperature or below. Spectral analysis show the red colors to be associated with the intermolecular 1:1 electron donor-acceptor (EDA) complexes between the enol silyl ether and TNM. The formation of similar vividly colored EDA complexes with other electron acceptors (such as chloranil, tetracyanobenzene, tetracyanoquinodimethane, etc.) readily establish enol silyl ethers to be excellent electron donors. The deliberate irradiation of the diagnostic (red) charge-transfer absorption bands of the EDA complexes of enol silyl ethers and TNM at -40 °C affords directly the same α-nitro ketones, under conditions in which the thermal reaction is too slow to compete. A common pathway is discussed in which the electron transfer from the enol silyl ether (ESE) to TNM results in the radical ion triad [ESE?+, NO2?, C(NO2)3-]. A subsequent fast homolytic coupling of the cation radical of the enol silyl ether with NO2? leads to the α-nitro ketones. The use of time-resolved spectroscopy and the disparate behavior of theisomeric enol silyl ethers of α- and β-tetralones as well as of 2-methylcyclohexanone strongly support cation radicals (ESE?+) as the critical intermediate in thermal and photoinduced electron-transfer as described in Schemes 1 and 2, respectively.
- Rathore, Rajendra,Kochi, Jay K.
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p. 627 - 639
(2007/10/03)
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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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p. 5532 - 5536
(2007/10/03)
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- Photoinduced electron transfer from enol silyl ethers to quinone. Part 1. Pronounced effects of solvent polarity and added salt on the formation of α-enones
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The enol silyl ethers (ESE) of various ketones are efficiently oxidized to the corresponding α, β-unsaturated enones (E) when a dichloromethane solution containing equimolar amounts of chloranil is irradiated with filtered light (λexc > 380 nm). The 1:1 adduct (A) of enol silyl ether and quinone is a byproduct, the structure of which is established by X-ray crystallography. Solvent polarity and added salts play a major role in establishing the product distribution between E and A. Such a medium effect, coupled with the ready isomerization of the kinetic-thermodynamic isomers derived from the silylation of 2-methylcyclohexanone, points to the cation radical of the enol silyl ether (ESE.+) as the reactive intermediate. A radical-ion pair mechanism involving the rapid one-electron oxidation of enol silyl ethers by photoactivated chloranil is discussed.
- Bockman, T. Michael,Shukla,Kochi, Jay K.
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p. 1623 - 1632
(2007/10/03)
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- Photoinduced Molecular Transformations. Part 155. General Synthesis of Macrocyclic Ketones based on a Ring Expansion involving a Selective β-Scission of Alkoxyl Radicals, its Applications to a New Synthesis of (+/-)-Isocaryophyllene and (+/-)-Caryophyllene, and a Conformational Analy...
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The method used for a general synthesis of macrocyclic ketones based on a ring expansion involving a selective β-scission of alkoxyl radicals devised by Suginome and Yamada was extended and modified.Thus, cycloalkanones were transformed into the corresponding α-(ω-iodoalkyl)-cycloalkanones by alkylation of the corresponding lithium enolates with either 1,3-diiodopropane or 1,4-diiodobutane.Treatment of these α-iodoalkyl cyclic ketones with samarium iodide gave bicyclic tertiary alcohols.The generation of the alkoxyl radicals from the bicyclic alcohols by irradiation of the corresponding hypoiodites generated with mercury(II) oxide - iodine - pyridine in benzene resulted in a selective β-scission of their ring-junction bond to give high yields of macrocyclic ketones carrying an iodine which can be removed with tributyltin hydride.The method was then applied to new syntheses of (+/-)-isocaryophyllene and (+/-)-caryophyllene.Thus, ω-iodopropylation of ethyl 7,7-dimethyl-2-oxobicyclooctane-3-carboxylate, followed by cyclization of the resulting α-(ω-iodoalkyl)cycloalkanone with samarium diiodide, gave cis-transoid-cis-ethyl 1-hydroxy-4,4-dimethyltricyclo2,5>undecane-8-carboxylate (69percent).The ethoxycarbonyl group of this tricyclic alcohol was transformed into a methyl group by the standard method.Irradiation of a solution of the hypoiodite, prepared by the method mentioned above, with Pyrex-filtered light gave the corresponding cis-bicycloundecenone (15percent), its exomethylene isomer (2,5>undecan-1-ol mentioned above were correlated with the three products.
- Suginome, Hiroshi,Kondoh, Takahiko,Gogonea, Camelia,Singh, Vishwakarma,Goto, Hitoshi,Osawa, Eiji
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- Highly regio and stereoselective preparation of Z silyl enol ethers and Z enol esters from ketones via manganese enolates
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Mn-enolates are easily and quantitatively obtained under mild conditions (THF, -10°C to rt, 1 h) by treatment of ketones with aromatic Mn-amides such as Ph(Me)NMnZ. They allow to prepare Z silyl enol ethers and Z enol esters in high yields and with an exc
- Cahiez, Gerard,Figadere, Bruno,Clery, Patrick
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p. 6295 - 6298
(2007/10/02)
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- TRIMETHYLSILYLFLUOROSULFONATE (TMSOFs): AN ALTERNATIVE TO TMS TRIFLATE AS A SOURCE OF Me3Si+
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Generation of trimethylsilylfluorosulfonate in situ provides a useful source of TMS+, the reactivity of which is essentially equivalent to that of TMS triflate.Its precursors, in particular FSO3H, are less costly than those of TMSOTf or the reagent itself.
- Lipshutz, Bruce H.,Burgess-Henry, Jana,Roth, Gregory P.
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p. 995 - 998
(2007/10/02)
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- Lewis Acid Catalysed Michael-type Addition. A New Regio- and Diastereoselective Annulation Method using Methyl Vinyl Ketone
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A new annulation method is presented, involving a boron trifluoride catalysed Michael addition of trialkylsilyl enol ethers to methyl vinyl ketone (MVK) in the presence of a hydroxylic compound.This methodology allows regiospecific 3-oxobutylation of eith
- Duhamel, Pierre,Dujardin, Gilles,Hennequin, Laurent,Poirier, Jean-Marie
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p. 387 - 396
(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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- Azilidine-Trimethylsilyl Bromide-Ph4SbBr System as a Novel Selective Reagent for Synthesis of Silyl Enol Ethers from Cyclic Ketones
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Azilidine-trimethylsilyl bromide-tetraphenylstibonium bromide system is an effective reagent to produce silyl enol ethers from cyclic ketones.This had the specific selectivity to silylate cyclic ketones exclusively even in the case of coexsisting with acyclic ketones.
- Fujiwara, Masahiro,Baba, Akio,Matsuda, Haruo
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p. 1247 - 1250
(2007/10/02)
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- α-ALKYLATION AND α-ALKYLIDENATION OF CARBONYL COMPOUNDS BY O-SILYLATED ENOLATE PHENYLTHIOALKYLATION
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For many reactions next to a carbonyl group, the use of O-silylated enolate chemistry offers improvements in yield and selectivity over the corresponding reactions of Group I metal enolates.In the case of α-alkylation of carbonyl compounds, Lewis acid (TiCl4 or ZnBr2) promoted phenylthioalkylation of O-silylated enolates 3 by α-chlorosulphides 4 (R3=H, Me, Prn, Pri, Bui, and Me3Si), followed by reductive sulphur removal by Raney nickel, 5->6, is found to be a reliable method for this synthetically important C-C bond forming step.An alternative sulphur elimination pathway via the sulphoxide, 5->7, allows the regio- and stereocontrolled α-alkylidenation of carbonyl compounds.The phenylthioalkylation reaction is applicable to ketones, aldehydes, esters, and lactones.
- Paterson, Ian
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p. 4207 - 4220
(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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- A Convenient Regioselective Synthesis of Mannich Bases
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A new, convenient regioselective process for aminomethylation of ketones is reported, involving the in situ formation of silyl enol ethers and iminium salts.
- Rochin, C.,Babot, O.,Dunogues, J.,Duboudin, F.
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p. 667 - 668
(2007/10/02)
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- Reagents and synthetic methods. 31. Silylations with N-trimethylsilyl-2-oxazolidinone (TMSO)
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Silylation of ketones, alcohols, mercaptans, and carboxylic acids with N-trimethylsilyl-2-oxazolidinone (TMSO) and triflic acid as catalyst has been described from synthetic and mechanistic points of view.
- Aizpurua, Jesus M.,Palomo, Claudio,Palomo, Antonio L.
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p. 336 - 340
(2007/10/02)
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- Preparation of a New, Highly Reactive Form of Iron(0) and Its Use in Deprotonation of Carbonyl Compounds
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A new, highly reactive form of zerovalent iron, prepared from the reaction of methylmagnesium bromide and ferric chloride, has been found to deprotonate cyclic unsymmetrical ketones in the presence of trimethylsilyl chloride to give thermodynamic (more substituted) silyl enol ethers regiospecifically.
- Krafft, Marie E.,Holton, Robert A.
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p. 3669 - 3670
(2007/10/02)
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- Pyridylseleno Group in Organic Synthesis. Preparation and Oxidation of α-(2-Pyridylseleno) Carbonyl Compounds Leading to α,β-Unsaturated Ketones and Aldehydes
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α-(2-Pyridylseleno) carbonyl compounds (A) were prepared by the reaction of ketones or aldehydes with 2-pyridylselenenyl bromide under various conditions (acidic, basic, or after conversion to silyl enol ethers) in good to excellent yields.Oxidation of A thus prepared affords α,β-unsaturated carbonyl compounds in excellent yields even in the cases where satisfactory results were not obtained by the oxidation of the corresponding α-phenylseleno carbonyl compounds.These results indicate that the 2-pyridylseleno group is a better leaving group than the phenylseleno group in selenoxide elimination leading to enones.
- Toshimitsu, Akio,Owada, Hiroto,Terao, Keiji,Uemura, Sakae,Okano, Masaya
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p. 3796 - 3800
(2007/10/02)
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- REGIOSPECIFIC PREPARATION OF THERMODYNAMIC SILYL ENOL ETHERS USING BROMOMAGNESIUM DIALKYLAMIDES
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Thermodynamic silyl enol ethers are regiospecifically generated in high yield from cyclic ketones, bromomagnesium diisopropylamide (BMDA) and trimethylsilyl chloride.
- Krafft, M. E.,Holton, Robert A.
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p. 1345 - 1348
(2007/10/02)
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- VINYL CATIONS. 40. pi - AND sigma -ROUTES TO VINYL CATIONS. SOLVOLYSES OF 2-METHYLCYCLOHEXENYL, CYCLOPENTYLIDENEETHYL, HEX-5-YN-1-YL, AND RELATED TRIFLATES.
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Three triflates were solvolyzed at various temperatures in water-alcohol mixtures, in TFE-water mixtures, in TFA, in TFIP, in HFIP, and in 100% TFE in the presence of various buffers and the resulting products were determined. The three reactants were also solvolyzed in a standard mixture (1:100:100 equals triflate:TFE:Na//2CO//3) at various temperatures, and the yields of products were compared. The solvolysis products were shown to be under kinetic control.
- Hanack,Fuchs,Collins
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p. 4008 - 4017
(2007/10/12)
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- A REGIOSPECIFIC SYNTHESIS OF γ-KETO ESTERS: THE ALKYLATION OF O-SILYLATED ENOLATES WITH METHYL α-CHLORO-α-PHENYLTHIOACETATE
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Methyl α-chloro-α-phenylthio acetate (2) regiospecifically alkylates O-silylated enolates to form γ-keto esters.
- Lee, Thomas V.,Okonkwo, Jonathan O.
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p. 323 - 326
(2007/10/02)
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- HIGHLY REGIOSELECTIVE GENERATION OF "THERMODYNAMIC" ENOLATES AND THEIR DIRECT CHARACTERIZATION BY NMR
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Addition of 2-methylcyclohexanone to 1.05 equiv of KH suspended in THF, followed by treatment with 1.25 equiv of BEt3 gives potassium enoxyborate 2a as a 90-95percent regioisomerically pure species, as judged by its 1H and 13C NMR as well as by GLC analysis of the silylated products, while the use of KN(SiMe3)2 in place of KH gives 1a as a 90-95percent pure substance.The KH-BEt3 procedure also gives 4 and 5 as 91 and 85percent regiochemically pure species, respectively.
- Negishi, Ei-ichi,Chatterjee, Sugata
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p. 1341 - 1344
(2007/10/02)
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- THE REACTION OF CHROMYL CHLORIDE AND O-SILYLATED ENOLATES: A NOVEL REGIOSPECIFIC ROUTE TO α-HYDROXY KETONES.
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Chromyl chloride reacts regiospecifically with O-silylated enolates to form α-hydroxy ketones.
- Lee, Thomas V.,Toczek, Judy
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p. 2917 - 2920
(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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- Acylation of Ketone Silyl Enol Ethers with Acetyl Tetrafluoroborate. A Synthesis of 1,3-Diketones
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Silyl enol ethers, obtained by silylation of ketones, are acylated with acetyl tetrafluoroborate to give 1,3-diketones in reasonable yields.Thetert-butyldimethylsilyl enol ether of cyclohexanone gives a nearly quantitative yield of acetylcyclohexanone, while the trimethylsilyl enol ethers of cyclohexanone and other ketones give moderate yields of the corresponding 1,3-diketones.The regiospecificity of the reaction was studied with the isomeric silyl enol ethers of 2-methylcyclohexanone.
- Kopka, Ihor,Rathke, Michael W.
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p. 3771 - 3773
(2007/10/02)
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- Use of 1,8-Diazabicycloundec-7-ene in Preparation of Trimethylsilyl Enol Ethers and Trimethylsilylacetylenes
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Trimethylsilyl enol ethers were prepared by using a combination of chlorotrimethylsilane and 1,8-diazabicycloundec-7-ene in good yields.Trimethylsilylation of acetylenes was also achieved with the same reagents in the presence of silver salt as catalyst.
- Taniguchi, Yoshiyuki,Inanaga, Junji,Yamaguchi, Masaru
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p. 3229 - 3230
(2007/10/02)
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- Preparation of 1,3-Diketones and of Nitro-diketones by (1:1)-Acylation of Lithium Enolates with Acyl Chlorides
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Slow addition of precooled solutions of lithium enolates in THF to solutions of equimolar amounts of acyl chlorides in the same solvent at temperatures between -80 and -100 deg furnishes 1,3-diketones in acceptable to good yields.Even 3-nitropropionyl and 4-nitrobutyryl chloride can be employed for the (1:1)-acylation of enolates to give the synthetically useful 5- and 6-nitro-1,3-diketones 13 and 25, respectively.The scope and the limitations of this method of preparing 1,3-diketones are given and are compared with alternative methods.
- Seebach, Dieter,Weller, Thomas,Protschuk, Gerd,Beck, Albert K.,Hoekstra, Marvin S.
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p. 716 - 735
(2007/10/02)
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- METHODE SIMPLE POUR LA SYNTHESE RAPIDE ET STEREOSELECTIVE D'ENOXYSILANES D'ALDEHYDES ET DE CETONES
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A new highly regio- and stereo-selective method for the preparation of enoxysilanes, viz. treatment of Me3SiCl, NaI, Et3N with enolizable aldehydes and ketones is described.
- Cazeau, Philippe,Moulines, Francoise,Laporte, Odile,Duboudin, Francoise
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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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- 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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