- Enyne-2-pyrone [4 + 4]-Photocycloaddition: Sesquiterpene Synthesis and a Low-Temperature Cope Rearrangement
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Intramolecular [4 + 4] photoreaction of 2-pyrones with a 1,3-enyne yields an unstable 1,2,5-cyclooctatriene product. Without a C4 pyrone substituent, 1,3-hydrogen migration converts the allene to a 1,3-diene, with a skeleton related to dactylol. With methoxy substitution, Cope rearrangement yields a nine-membered ring fused to a cyclobutane. Both structures were confirmed by X-ray crystallography. The Cope rearrangement is apparently reversible, reforming the allene which undergoes a proton shift to the more stable 1,3-diene product.
- Khatri, Buddha B.,Sieburth, Scott McN.
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Read Online
- Kinetics of the Siloxyvinylcyclopropane Rearrangement Using a Micro Stirred Flow Reactor
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The kinetics of the thermal rearrangement of 1-(1-(trimethylsiloxy)cyclopropyl)cyclopentene (3), 5-methyl-1-(1-(trimethylsiloxy)cyclopropyl)cyclopentene (5), 1-cyclopropyl-1-(trimethylsiloxy)ethylene (7), and 1-((Z)-2-methyl-1-(trimethylsiloxy)cyclopropyl)cyclopentene (9) was investigated on a micro stirred flow apparatus.Siloxyvinylcyclopropanes 3, 5, and 7 rearrange cleanly to their respective cyclopentyl enol silyl ethers with a calculated ΔG% (350 deg C) of 43.8 kcal/mol for 3, 42.9 kcal/mol for 5, and 51.3 kcal/mol for 7.Siloxyvinylcyclopropane 9 rearranged to4-cyclopentylidene-4-(trimethylsiloxy)but-1-ene (10) via the homo 1,5 hydrogen shift with a calculated ΔG% (350 deg C) of 39.2 kcal/mol.A comparison of the ΔG%-s for the rearrangement of siloxyvinylcyclopropanes is made with those of other substituted vinylcyclopropanes.
- Trost, Barry M.,Scudder, Paul H.
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- Boron Trifluoride-Mediated Cycloaddition of 3-Bromotetrazine and Silyl Enol Ethers: Synthesis of 3-Bromo-pyridazines
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Pyridazines are important scaffolds for medicinal chemistry or crop protection agents, yet the selective preparation of 3-bromo-pyridazines with high regiocontrol remains difficult. We achieved the Lewis acid-mediated inverse electron demand Diels-Alder reaction between 3-monosubstituted s-tetrazine and silyl enol ethers and obtained functionalized pyridazines. In the case of 1-monosubstituted silyl enol ethers, exclusive regioselectivity was observed. Downstream functionalization of the resulting 3-bromo-pyridazines was demonstrated utilizing several cross-coupling protocols to synthesize 3,4-disubstituted pyridazines with excellent control over the substitution pattern.
- Schnell, Simon D.,González, Jorge A.,Sklyaruk, Jan,Linden, Anthony,Gademann, Karl
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p. 12008 - 12023
(2021/08/24)
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- 1,2-Carbopentafluorophenylation of Alkynes: The Metallomimetic Pull-Push Reactivity of Tris(pentafluorophenyl)borane
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We report the novel single-step 1,2-dicarbofunctionalization of an arylacetylene with an allylsilane and tris(pentafluorophenyl)borane [B(C6F5)3] involving C?C bond formation with C?H bond scission at the β-position to the silicon atom of an allylsilane and B→C migration of a C6F5 group. The 1,2-carbopentafluorophenylation occurs smoothly without the requirement for a catalyst or heating. Mechanistic studies suggest that the metallomimetic “pull-push” reactivity of B(C6F5)3 imparts consecutive electrophilic and nucleophilic characteristics to the benzylic carbon of the arylacetylene. Subsequent photochemical 6π-electrocyclization affords tetrafluoronaphthalenes, which are important in the pharmaceutical and materials sciences. Owing to the unique reactivity of B(C6F5)3, the 1,2-carbopentafluorophenylation using 2-substituted furan proceeded with ring opening, and the reaction using silyl enolates formed a C?C bond with C?O bond scission at the silyloxy-substituted carbon.
- Shibuya, Masatoshi,Matsuda, Miki,Yamamoto, Yoshihiko
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supporting information
p. 8822 - 8831
(2021/05/21)
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- Three-Component Coupling of Acyl Fluorides, Silyl Enol Ethers, and Alkynes by P(III)/P(V) Catalysis
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We report herein on the phosphine-catalyzed hydrovinylation reaction by three-component coupling of acyl fluorides, silyl enol ethers, and alkynoates. The key to the success of the reaction is the formal transmetalation between pentacoordinate P(V) species (i.e., fluorophosphorane) and a silyl enol ether, which allows for C-C bond formation between the polarity-mismatched sites. The bond formation that cannot be attained even by transition metal catalysis is accomplished by a P(III)/P(V) manifold.
- Fujimoto, Hayato,Kusano, Momoka,Kodama, Takuya,Tobisu, Mamoru
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supporting information
p. 18394 - 18399
(2021/11/22)
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- Visible light-mediated intermolecular [2 + 2] photocycloaddition of 1-aryl-2-nitroethenes and olefins
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Despite the importance of cyclobutanes there are not many direct [2 + 2] photocycloaddition reactions which can be performed with visible light in the absence of a catalyst. A notable exception is the reaction of 1-aryl-2-nitroethenes and olefins which can be performed at a wavelength of λ = 419 nm or λ = 424 nm in CH2Cl2 as the solvent. In the present study, a total of 15 1-aryl-2-nitroethenes were found to undergo a [2 + 2] photocycloaddition with 2,3-dimethyl-2-butene (28-86% yield) and a set of 12 olefins was studied in their photocycloaddition to 1-phenyl-2-nitroethene (37-88% yield). All mechanistic results are in agreement with a triplet reaction pathway and with the intermediacy of a 1,4-diradical.
- Mohr, Lisa-Marie,Bauer, Andreas,Jandl, Christian,Bach, Thorsten
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supporting information
p. 7192 - 7203
(2019/08/07)
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- Unprecedented alkylation of silicon enolates with alcohols via carbenium ion formations catalyzed by tin hydroxide-embedded montmorillonite
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The solid acid, tin hydroxide-embedded montmorillonite, catalyzes the unprecedented alkylation of various silicon enolates with primary, secondary and tertiary benzylic alcohols as well as secondary allylic alcohols. The acid catalysis of Sn-Mont was not only higher than that of the other ion-exchanged montmorillonites (M-Mont; M?=?H, Ti, Fe and Al), but also higher than that of the typical homogeneous acid catalysts such as BF3·OEt2, TMSOTf and TfOH.
- Tandiary, Michael Andreas,Asano, Masashi,Hattori, Taiki,Takehira, Satoshi,Masui, Yoichi,Onaka, Makoto
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supporting information
p. 1925 - 1928
(2017/04/27)
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- Stereoselective and Regioselective Pinacol-Type Rearrangement of a Fused Bicyclic Oxetanol Scaffold
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The Paternò-Büchi reaction between benzaldehyde and trimethylsilyloxycyclopentene gave access to an unprecedented silyl ether derivative of 6-oxabicyclo[3.2.0]heptan-1-ol. The bicyclic structure underwent selective reductive ring opening and acid-catalyzed pinacol-type rearrangement reactions with complete regioselectivity, accompanied by moderate to excellent mechanism-dependent diastereoselectivity.
- Melis, Nicola,Luridiana, Alberto,Guillot, Régis,Secci, Francesco,Frongia, Angelo,Boddaert, Thomas,Aitken, David J.
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p. 5896 - 5902
(2017/10/31)
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- Chiral Br?nsted Acid as a True Catalyst: Asymmetric Mukaiyama Aldol and Hosomi-Sakurai Allylation Reactions
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Highly diastereo- and enantioselective Mukaiyama aldol reaction catalyzed by a new chiral Br?nsted acid, N-(perfluorooctanesulfonyl)thiophosphoramide, is described. The perfluorooctyl substituent on the sulfonyl group of the catalyst plays an essential role in the stereoselection. The catalyst also allows the asymmetric Hosomi-Sakurai allylation, which has been considerably challenging due to the low reactivity of allylsilanes. 29Si and 31P NMR monitoring reveals the characteristic feature of the thiophosphoramide catalyst, acting as a strong Br?nsted acid even in the presence of excess silyl nucleophiles, which cannot be found in other related phosphoric acid analogues.
- Sai, Masahiro,Yamamoto, Hisashi
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supporting information
p. 7091 - 7094
(2015/06/25)
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- Ring-contraction strategy for the practical, scalable, catalytic asymmetric synthesis of versatile γ-quaternary acylcyclopentenes
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Contraction action! A simple protocol for the catalytic asymmetric synthesis of highly functionalized γ-quaternary acylcyclopentenes (see schematic) in up to 91 % overall yield and 92 % ee has been developed. The reaction sequence employs a palladium-catalyzed enantioselective alkylation reaction and exploits the unusual stability of β-hydroxy cycloheptanones to achieve a general and robust method for performing two-carbon ring contractions. Copyright
- Hong, Allen Y.,Krout, Michael R.,Jensen, Thomas,Bennett, Nathan B.,Harned, Andrew M.,Stoltz, Brian M.
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supporting information; experimental part
p. 2756 - 2760
(2011/05/05)
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- Metal nitrite: A powerful oxidizing reagent
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An efficient and simple source of nitroso reagents and their oxidation reactions are described. The combination of a Lewis acid and a metal nitrite was applied to the oxidation of silyl enol ethers. Amino acid and peptide derivatives were easily accessed through in situ C-C bond cleavage of fully substituted silyl enol ethers upon oxidation.
- Baidya, Mahiuddin,Yamamoto, Hisashi
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supporting information; body text
p. 13880 - 13882
(2011/10/09)
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- ScIII-Doped zeolites as new heterogeneous catalysts: mukaiyama aldol reaction
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ScIII-doped solids based on zeolite materials have been investigated for the first time as catalysts in organic synthesis. Sc III-USY zeolite proved to be a novel and very efficient heterogeneous catalyst for the Mukaiyama aldol reaction. This easy-to-prepare catalyst exhibited wide scope and compatibility with functional groups and is very simple to use, easy to remove (by simple filtration), and is recyclable (up to three times without loss of activity).
- Olmos, Andrea,Alix, Aurelien,Sommer, Jean,Pale, Patrick
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supporting information; experimental part
p. 11229 - 11234
(2010/04/28)
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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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- Di-tert-butylmagnesium as an atom-efficient, carbon-centred base reagent for the preparation of silyl enol ethers from ketones
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Di-tert-butylmagnesium has been found to be a reactive, yet non-nucleophilic and non-reductive, carbon-centred base for the deprotonation of a series of ketones. This reagent demonstrates equally high reactivity when used as either the pre-formed reagent, or in a more accessible one-pot protocol from the parent Grignard reagent, and offers improved atom-efficiency over more traditionally employed bases. Georg Thieme Verlag Stuttgart.
- Kerr, William J.,Watson, Allan J. B.,Hayes, Douglas
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experimental part
p. 1386 - 1390
(2009/04/06)
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- In situ generation of Mes2Mg as a non-nucleophilic carbon-centred base reagent for the efficient one-pot conversion of ketones to silyl enol ethers
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Treatment of commercially available MesMgBr with 1,4-dioxane produces the key Mes2Mg reagent in situ which then mediates the deprotonation of ketones to deliver trimethylsilyl enol ethers, at readily accessible temperatures and without any nucleophilic addition, in an expedient and high yielding one-pot process. The Royal Society of Chemistry.
- Kerr, William J.,Watson, Allan J. B.,Hayes, Douglas
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experimental part
p. 1238 - 1243
(2008/10/09)
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- Sc(OTf)3-catalyzed smooth tandem [3+2] cycloaddition/ring opening of donor-acceptor cyclopropane 1,1-diesters with enol silyl ethers
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Catalyzed by Lewis acids, donor-acceptor cyclopropane 1,1-diesters reacted with enol silyl ethers to afford 1,6-dicarbonyl compounds in moderate to excellent yields. This supplied a mild carbon-carbon bond-forming method from the ring opening of cyclopropanes. A smooth tandem [3+2] cycloaddition/ring opening process has been clearly proved by an independent experiment.
- Fang, Jie,Ren, Jun,Wang, Zhongwen
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supporting information; body text
p. 6659 - 6662
(2009/04/07)
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- Bismesitylmagnesium: A thermally stable and non-nucleophilic carbon-centred base reagent for the efficient preparation of silyl enol ethers
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Bismesitylmagnesium has been established as an accessible, practical, convenient, and non-nucleophilic carbon-centred base reagent for efficient access to silyl enol ethers from a series of ketone substrates at readily utilisable temperatures. The Royal Society of Chemistry.
- Kerr, William J.,Watson, Allan J. B.,Hayes, Douglas
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p. 5049 - 5051
(2008/09/17)
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- 3-Fluoro-6-tert-butyltetrahydropyranosyl trichloroacetamidates. "Chiral auxiliary donors" for hydroxyalkyl radicals
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An improved THP-based chiral auxiliary for hydroxyalkyl radicals is reported. The key modifications involve introduction of a fluorine substituent at C-3 to make the acetal center more robust and the use of Schmidt's trichloroacetamidate glycosylation methodology for efficient attachment of the auxiliary to the radical precursor. The resulting chiral hydroxyalkyl radical equivalents add to methyl 2-trifluoroacetoxyacrylate with selectivities ranging from 9:1 (0°C) to 15:1 (-78°C).
- Garner, Philip,Sesenoglu, Oezge
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p. 1217 - 1219
(2007/10/03)
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- Kinetic resolution of tert-butyl (RS)-3-alkylcyclopentene-1-carboxylates for the synthesis of homochiral 3-alkyl-cispentacin and 3-alkyl-transpentacin derivatives
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High levels of stereocontrol are observed in the conjugate addition of lithium dibenzylamide to tert-butyl (RS)-3-alkylcyclopentene-l-carboxylates (alkyl = Et, Bn), with addition occurring exclusively anti- to the 3-alkyl substituent. Treatment of a range of tert-butyl (RS)-3-alkylcyclopentene-l-carboxylates (alkyl = Et, Bn, 'Pr, 'Bu) with lithium (RS)-N-benzyl-N-α-methylbenzylamide indicates that good enantiorecognition is observed (E > 80) in their mutual kinetic resolution. In these reactions, conjugate addition of the lithium amide occurs exclusively anti- to the 3-alkyl substituent, with subsequent C(1)-protonation occurring preferably anti- to the 2-amino group in the 3-Et, 3-Bn and 3-'Pr cases, giving predominantly the corresponding 1,2-syn-2,3-anti-diastereoisomers. Conjugate addition to (RS)-3-tert-butyl cyclopentene-l-carboxylate results in exclusive 2,3-anti-addition and a reversal in C(1)-protonation selectivity, giving predominantly the 1,2-anti-2,3-anti-diastereoisomer. Furthermore, the kinetic resolution of the tert-butyl (RS)-3-alkylcyclopentene-l-carboxylates (alkyl = Et, Bn, 'Pr, 'Bu) with lithium (S)-N-benzyl-N-αmethylbenzylamide proceeds efficiently, giving, at between 47 and 51% conversion, the resolved 3-alkylcyclopentene-l-carboxylates in >85 to >98% ee and the β-amino ester products of conjugate addition in high de, consistent with E > 80 in each case. Subsequent deprotection of the 1,2-syn-2,3-anti-3-alkyl-β-amino esters (alkyl = Et, Bn, 'Pr) by hydrogenolysis and ester hydrolysis gives the corresponding 1,2-syn-2,3-anti-3-alkylcispentacins in >98% de and 98 ±1% ee. Selective epimerisation of the 1,2-syn-2,3-anti-3-alkyl-β-amino esters (alkyl = Et, Bn, 'Pr, 'Bu) by treatment with KO'Bu in 'BuOH gives the corresponding 1,2-anti-2,3-anti-3-alkyl-β-amino esters in quantitative yield and in >98% de, with subsequent deprotection by hydrogenolysis and ester hydrolysis giving the corresponding 1,2-anti-2,3-anti-3-alkylcispentacin hydrochlorides in >98% de.
- Bunnage, Mark E.,Davies, Stephen G.,Parkin, Richard M.,Roberts, Paul M.,Smith, Andrew D.,Withey, Jonathan M.
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p. 3337 - 3354
(2007/10/03)
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- 4-Phenylbutanoyl-2(S)-acylpyrrolidines and 4-phenylbutanoyl-L-prolyl-2(S)-acylpyrrolidines as prolyl oligopeptidase inhibitors
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New 4-phenylbutanoyl-2(S)-acylpyrrolidines and 4-phenylbutanoyl-L-prolyl-2(S)-acylpyrrolidines were synthesized. Their inhibitory activity against prolyl oligopeptidase from pig brain was tested in vitro. In the series of 4-phenylbutanoyl-2(S)-acylpyrrolidines, the cyclopentanecarbonyl and benzoyl derivatives were the best inhibitors having IC50 values of 30 and 23 nM, respectively. This series of compounds shows that the P1 pyrrolidine ring, which is common in most POP inhibitors, can be replaced by either a cyclopentyl ring or a phenyl ring, causing only a slight decrease in the inhibitory activity. In the series of 4-phenylbutanoyl-L-prolyl-2(S)-acylpyrrolidines the cyclopentanecarbonyl and benzoyl derivatives were not as active as in the series of 4-phenylbutanoyl-2(S)-acylpyrrolidines. The hydroxyacetyl derivative did however show high inhibitory activity. This compound is structurally similar to JTP-4819, which is one of the most potent prolyl oligopeptidase inhibitors. The acyl group in the two series of new compounds seems to bind to different sites of the enzyme, since the second series of new compounds did not show the same cyclopentanecarbonyl or benzoyl specificity as the first series.
- Wallen, Erik A.A.,Christiaans, Johannes A.M.,Saario, Susanna M.,Forsberg, Markus M.,Venaelaeinen, Jarkko I.,Paso, Hanna M.,Maennistoe, Pekka T.,Gynther, Jukka
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p. 2199 - 2206
(2007/10/03)
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- Method of synthesis of pyrrole amides
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A method for preparing pyrrole-carboxyamides which selectively bind to GABAa receptors; which comprises reacting 1,3-cycloakane-diones with bromoethylacetate followed by reaction of the resulting product with an acid halide followed by reaction with an aromatic amine and finally with an amonium source at an elevated temperature.
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- Investigation of methods for seven-membered ring synthesis: A practical synthesis of 4-oxo-5,6,7,8-tetrahydro-4h-cyclohepta[b]furan-3-carboxylic acid
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Several synthetic routes to 4-oxo-5,6,7,8-tetrahydro-4H-cyclohepta[b]furan-3-carboxylic acid (1) are described, and the scale-up issues with each route are discussed. Seven-membered ring formation is a key issue with these syntheses, and several strategies are presented, including preparation from cycloheptane-1,3-dione, ring-expansion routes, Dieckmann cyclization, acetylene-furan [4 + 2] cycloaddition, and Friedel-Crafts cyclization. Two of the routes were scaled in the pilot plant to provide kilogram quantities of the title compound. The first scale-up route is outlined in Scheme 2 and utilizes a ring-expansion strategy to prepare cycloheptane-1,3-dione from cyclopentanone, via a [2 + 2] cycloaddition between dichloroketene and the silyl enol ether of cyclopentanone. The diketone is converted to the title compound by condensation with ethyl bromopyruvate and base, followed by acid hydrolysis. This route was efficient on laboratory scale but encountered problems upon scale-up due to a competing fragmentation pathway in the Zn/AcOH-mediated retro-aldol of cyclobutanone 11. The second, more successful scale-up route is described in Scheme 15, and involves Friedel-Crafts acylation of 3-carboethoxyfuran selectively at the 5-position. Reduction, lactonization, and hydrogenolysis provide acid 43, which is cyclized via a second Friedel-Crafts reaction to form the seven-membered ketone.
- Ragan, John A.,Murry, Jerry A.,Castaldi, Michael J.,Conrad, Alyson K.,Jones, Brian P.,Bryan, Li,Makowski, Teresa W.,McDermott, Ruth,Sitter, Barb J.,White, Timothy D.,Young, Gregory R.
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p. 498 - 507
(2013/09/07)
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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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- A practical synthesis of cycloheptane-1,3-dione
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A three-step synthesis of cycloheptane-1,3-dione has been developed which avoids the use of heavy metal or explosive reagents and provides access to multigram quantities of this material.
- Ragan, John A.,Makowski, Teresa W.,Amende, David J.,Clifford, Pamela J.,Young, Gregory R.,Conrad, Alyson K.,Eisenbeis, Shane A.
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p. 379 - 381
(2013/09/08)
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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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- 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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- 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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- 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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- Intramolecular Cyclizations of α-Stannyl Radicals to Acylsilanes: Regiospecific Syntheses of Five-membered Cyclic Silyl Enol Ethers
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α-Stannyl radicals generated from acylsilanes 5, 13 and 14 cyclize to give good yields of cyclic silyl enol ethers after sequential cyclizations, radical Brook rearrangements and β-scissions.
- Tsai, Yeun-Min,Chang, Sheng-Yueh
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p. 981 - 982
(2007/10/02)
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- A simple procedure for the synthesis of 3-(substituted-sulfanyl)-4-hydroxy-6-substituted-pyran-2-ones
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A series of 3-(substituted sulfanyl)-4-hydroxy-6-substituted-pyran-2-ones were synthesized for Human immunodeficiency virus-1 protease inhibition. These compounds were synthesized in a simple and convergent fashion to allow us a rapid preparation of many structurally diversified analogues. Thus the condensation of trimethylsilyl enol ethers of corresponding ketones, with 2-(S-substituted)propane-1,3-dioates afforded the corresponding pyrones in 24-70% isolated yields.
- Para,Ellsworth,Vara Prasad
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p. 1619 - 1624
(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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- 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 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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- Acyclic Stereoselection. 36. Simple Diastereoselection in the Lewis Acid Mediated Reactions of Enol Silanes with Aldehydes
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The Lewis acid mediated aldol reactions of enol silanes with aldehydes have been investigated.The effects of enol silane structure, both nature of the ligand at the silyloxy carbon and the geometry of the double bond, the aldehyde structure, and the nature of the Lewis acid have been studied.In general, the reactions of prochiral enol silanes with prochiral aldehydes show little simple diastereoselection (Table I).An exception is Z enol silane 7, derived from ethyl tert-butyl ketone, which shows synthetically useful anti selectivity.Enol silane 36 may therefore be used as an anti-selective propionate equivalent.The chiral α-alkoxy aldehyde 43 shows a high diastereofacial preference in its reactions with enol silanes 42c and 42d provided a Lewis acid capable of expanding its coordination beyond four is used (TiCl4 or SnCl4) (Table II).However, with the related ketene acetal 41b, only modest diastereofacial selectivity is seen (Table II).Aldehyde 43 also shows a high diastereofacial preference, in the chelation-controlled sense, in its reactions with prochiral enol silanes 5-9.However, the simple diastereoselection observed in the latter reactions (Table III) is quite different from that observed in the reactions of prochiral aldehydes with the same enol silanes.For example, enol silane 7, which shows good anti selectivity in its reactions with prochiral aldehydes, gives a 15:1 mixture of the two syn aldols in its reaction with 43; while the reverse is true with the propiophenone-derived enol silanes 8 and 9.Finally, the results obtained in this study, along with those reported by other investigators, have been formulated into a coherent mechanistic rationale involving open transition states of the sort depicted in Figures 1 and 3.
- Heathcock, Clayton H.,Davidsen, Steven K.,Hug, Kathleen T.,Flippin, Lee A.
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p. 3027 - 3037
(2007/10/02)
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- Enol Ethers, XVII. Acylation of Trimethylsilyl Enol Ethers with Malonyl Dichloride - Synthesis of 4-Hydroxy-2H-pyran-2-ones
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Trimethylsilyl enol ethers of aldehydes 1, acyclic and cyclic ketones 4 and 10, respectively, are acylated by malonyl dichloride (2) at room temperature or even at -60 deg C.After aqueous workup, the 6-unsubstituted 4-hydroxy-2H-pyran-2-ones 3 are obtained from 1-(trimethylsiloxy)alkenes 1, whereas the 5,6-alkylene-bridged 4-hydroxy-2H-pyran-2-ones 11 are formed from 1-(trimethylsiloxy)cycloalkenes 10.Acylation of 2-(trimethylsiloxy)-1-propene (4a) and 3-(trimethylsiloxy)-2-pentene (4b) results in mixtures of 4-(trimethylsiloxy)-2H-pyran-2-ones 5 (main products) and phloroglucinol tris(trimethylsilyl) ethers (6) (by-products).
- Effenberger, Franz,Ziegler, Thomas,Schoenwaelder, Karl-Heinz,Kesmarszky, Thomas,Bauer, Bernd
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p. 3394 - 3404
(2007/10/02)
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- Synthese de quelques structures encombrees derivees de l'adamantane et de ses analogues par alkylation des ether d'enol trimethylsilyliques
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Alkylation of trimethylsilyl enol ethers of 2,4-dimethyl-3-pentanone, cyclopentanone and cyclohexanone has been extended to alkylating agents with a cage structure (substituted or functionalized adamantyl, diamantyl, homoadamantyl and noradamantyl chlorides or bromides).This method affords some new cage structured aliphatic and alicyclic ketones.In some cases one observes a new TiCl4 promoted reaction where the bromine in the alkylating agent is replaced by chlorine.This work is a generalization of our previous extended studies on α-alkylation of ketones with tertiary alkylating agents.
- Dubois, Jacques-Emile,Lebbar, Kadija,Lion, Claude,Dugast, Jean-Yves
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p. 905 - 910
(2007/10/02)
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- NOUVELLE SYNTHESE REGIOSELECTIVE DE β-ALCOXYCETONES A PARTIR D'ENOXYSILANES ET DE TRISENOXYSILANES ENGENDRES in situ
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An easy, regiospecific, route to β-alkoxyketones based on the use of methyl trichlorosilane for in situ generation of α-chloroethers and trisenoxysilanes is described.
- Rochin, Christophe,Babot, Odile,Duboudin, Francoise
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p. C24 - C28
(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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- 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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- Tertiobutylation de quelques cetones alicycliques et aliphatiques via leurs ethers d'enol trimethylsilyliques. Influence de l'environnement du carbonyle sur le deroulement de la reaction
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α-Tertiobutylation of aliphatic ketones via their trimethylsilyl enol ethers has been extended to the alicyclic series.A comparative study of the alkylation of ketones in both series with identical steric hindrance has been undertaken.The efficiency and limits of the reaction have been determinated by progressive substitution α and α' to the carbonyl.
- Lion, Claude,Dubois, Jacques-Emile
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p. 375 - 379
(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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- 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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- 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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- Chemistry of enol ethers. LI. Reaction of vinyl silyl ethers with orthoformic esters
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The silyl ethers of enolic forms of ketones react with orthoformates in the presence of zinc chloride at catalyst to form β-ketoacetals.The analogous reaction with the silyl ethers of enolic forms of aldehydes leads to the formation of the tetraacetals of 1,3-dialdehydes.
- Makin, S. M.,Kruglikova, R. I.,Popova, T. P.,Tagirov, T. K.
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p. 630 - 634
(2007/10/02)
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