- A convenient and selective method for preparation of enol acetates from ketones using montmorillonite KSF clay
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The reaction of ketones with stoichiometric amounts of acetic anhydride and Montmorillonite KSF clay at room temperature afforded the corresponding enol acetates in excellent yields. It has also been observed that by performing the reactions under microwave irradiation the reaction time can be dramatically reduced.
- Kalita, Biswajit,Bezbarua, Maitreyee Sarma,Barua, Nabin C.
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Read Online
- A selective catalytic method of enol-acetylation under microwave Irradiation
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Six-membered cyclic ketones on treatment with acetic anhydride and a catalytic amount of iodine under microwave irradiation give the corresponding enol acetates in good yield.
- Kalita, Dipok J.,Borah, Ruli,Sarma, Jadab C.
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Read Online
- Porphyrins as Photoredox Catalysts in Csp2-H Arylations: Batch and Continuous Flow Approaches
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We have investigated both batch and continuous flow photoarylations of enol-acetates to yield different α-arylated aldehyde and ketone building blocks by using diazonium salts as the aryl-radical source. Different porphyrins were used as SET photocatalysts, and photophysical as well as electrochemical studies were performed to rationalize the photoredox properties and suggest mechanistic insights. Notably, the most electron-deficient porphyrin (meso-tetra(pentafluorophenyl)porphyrin) shows the best photoactivity as an electron donor in the triplet excited state, which was rationalized by the redox potentials of excited states and the turnover of the porphyrins in the photocatalytic cycle. A two-step continuous protocol and multigram-scale reactions are also presented revealing a robust, cost-competitive, and easy methodology, highlighting the significant potential of porphyrins as SET photocatalysts.
- De Souza, Aline A. N.,Silva, Nathalia S.,Müller, Andressa V.,Polo, André S.,Brocksom, Timothy J.,De Oliveira, Kleber T.
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p. 15077 - 15086
(2019/01/03)
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- Study of the Reactivity of [Hydroxy(tosyloxy)iodo]benzene Toward Enol Esters to Access α-Tosyloxy Ketones
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The reactivity of enol esters toward [hydroxy(tosyloxy)iodo]benzene (HTIB) was assessed. These substrates were found to be rapidly converted in high yields to their corresponding α-tosyloxy ketones. This transformation demonstrates that these substrates can act as ketone surrogates. The scope of the method was investigated and aromatic, aliphatic, and cyclic enol esters were found to be suitable substrates for the reaction. The relative reactivity of a model substrate toward HTIB and m-CPBA was investigated, and it was found that the reaction could be performed under catalytic conditions.
- Basdevant, Benoit,Legault, Claude Y.
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p. 6897 - 6902
(2015/10/06)
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- Enantioselective Iodine(III)-Mediated Synthesis of α-Tosyloxy Ketones: Breaking the Selectivity Barrier
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The development of practical methods to access chiral nonracemic α-substituted ketones is of particular importance due to their ubiquitous nature. Unprecedented levels of enantioselectivity are reported for the synthesis of α-tosyloxy ketones, using enol esters and chiral iodine(III) reagents. The reaction can be performed under both stoichiometric and catalytic conditions. These results suggest widely different reaction mechanisms for the reaction of ketones versus enol esters, supporting recent computational insights.
- Basdevant, Benoit,Legault, Claude Y.
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supporting information
p. 4918 - 4921
(2015/10/12)
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- InCl3/Me3SiCl-catalyzed direct michael addition of enol acetates to α,β-unsaturated ketones
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The direct Michael addition of enol acetates to α,β-unsaturated ketones was achieved using a combination of Lewis acid catalysts, InCl 3 and Me3SiCl, which furnished stable enol-form products that could be further transformed into functionalized 1,5-diketones by reactions with various electrophiles.
- Onishi, Yoshiharu,Yoneda, Yuki,Nishimoto, Yoshihiro,Yasuda, Makoto,Baba, Akio
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supporting information
p. 5788 - 5791
(2013/01/15)
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- Visible-light-mediated α-arylation of enol acetates using aryl diazonium salts
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Visible light mediates efficiently the α-arylation of enol acetates by aryl diazonium salts under mild conditions using [Ru(bpy)3]Cl 2 as a photoredox catalyst. The broad scope of the reaction toward various diazonium salts and enol acetates was explored. The application of this reaction in the concise synthesis of 2-substituted indoles was demonstrated
- Hering, Thea,Hari, Durga Prasad,Koenig, Burkhard
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p. 10347 - 10352
(2013/01/15)
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- Titanium silicates as efficient catalyst for alkylation and acylation of silyl enol ethers under liquid-phase conditions
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The activity of titanium- and tin-silicate samples such as TS-1, TS-2, Ti-β and Sn-MFI has been investigated for acylation and alkylation of silyl enol ethers under mild liquid-phase conditions. Silyl enol ethers successfully react with acetyl chloride and tert-butyl chloride under dry conditions in the presence of above catalysts to produce the corresponding acylated and alkylated products, respectively. In the case of acetylation reaction, two different nucleophiles with carbon-center (C-atom) and oxygen-center (O-atom) in silyloxy group of silyl enol ether reacts with acetyl chloride to give 1,3-diketone and ketene-ester, respectively. The selectivity for alkylation is always ca. 100% and no side products are formed. Among the various solvents investigated, anhydrous THF was found to be the suitable solvent for alkylation; whereas dichloromethane exhibited high selectivity for diketones for acylation. The formation of nucleophiles from silyl enol ethers appears to be the key step for successful acetylation and tert-butylation by nucleophilic reaction mechanism. Sn-MFI showed less activity than that observed over the titanosilicates. The observed catalytic activity is explained on the basis of "oxophilic Lewis acidity" of titanium silicate molecular sieves in the absence of H 2O under dry reaction conditions.
- Sasidharan, Manickam,Bhaumik, Asim
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experimental part
p. 87 - 93
(2011/10/12)
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- InCl3/Me3SiBr-catalyzed direct coupling between silyl ethers and enol acetates
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A combined Lewis acid catalyst of InCl3 and Me3SiBr promoted the direct use of enol acetates in the coupling with low-reactive silyl ethers, in which functional groups including ketones and aldehydes survived. Sterically hindered silyl ethers such as ROSiEt3, ROSiPh3, ROSit-BuMe2, and ROSii-Pr3 were also applicable.
- Onishi, Yoshiharu,Nishimoto, Yoshihiro,Yasuda, Makoto,Baba, Akio
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supporting information; experimental part
p. 2762 - 2765
(2011/08/02)
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- InI3/me3sii-catalyzed direct alkylation of enol acetates using alkyl acetates or alkyl ethers
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A combined Lewis acid of InI3 and Me3SiI was used to catalyze the direct coupling reactions of enol acetates with alkyl acetates or alkyl ethers without generating metal waste. The easily-handled alkylating reagents enlarged the application area of this coupling reaction. 2011 The Chemical Society of Japan.
- Onishi, Yoshiharu,Nishimoto, Yoshihiro,Yasuda, Makoto,Baba, Akio
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supporting information; experimental part
p. 1223 - 1225
(2011/11/29)
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- Nucleophilic iron catalysis in transesterifications: Scope and limitations
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Figure presented The ester bond is one of the most common structural motifs found in nature. Apart from the condensation between an acid and an alcohol, transesterifications represent another mechanistic alternative for the preparation of this compound class. The present paper summarizes our most recent investigations in this field, using nucleophilic iron complexes as catalysts for transesterifications under neutral conditions. This new type of metal catalyst complements the existing methodologies, which rely on Lewis acidic metal complexes. Investigations on scope and limitations, stereochemical course, and chemoselectivities will be presented.
- Magens, Silja,Plietker, Bernd
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supporting information; experimental part
p. 3715 - 3721
(2010/08/07)
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- Practical synthesis of gem-difluorides from cyclohexanone: Synthesis of gem-bistrifluoroacetates and their reactions with fluoride nucleophiles
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Formation of ketone acylals bearing trihaloacetoxy groups and their nucleophilic geminal disubstitution by fluoride ions were investigated. Cyclohexanone reacted with trifluoroacetic anhydride without catalyst to give gem-bistrifluoroacetates via a concerted bimolecular reaction. Treatment with hydrogen fluoride under mild conditions efficiently yielded the corresponding gem-difluorides. In this reaction process, trifluoroacetic acid was recovered and converted to trifluoroacetic anhydride using P2O5. Since gem-difluorides were derived from ketones, HF and P2O5, this constitutes a practical synthesis of gem-difluorides.
- Tojo, Masahiro,Fukuoka, Shinsuke,Tsukube, Hiroshi
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experimental part
p. 29 - 35
(2010/03/30)
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- Process for Production of Carboxylic Acid Ester or Ether Compound
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Disclosed is a process for production of a carboxylic acid ester from a carboxylic acid and an olefin or production of an ether compound from an alcohol and an olefin at low cost and with high yield in an industrially advantageous manner. The process comprises the step of reacting a carboxylic acid with an olefin to yield a corresponding carboxylic acid ester or reacting an alcohol with an olefin to yield a corresponding ether compound. In the process, a catalyst comprising a combination of (i) at least one metal compound selected from an iron compound, a cobalt compound and a nickel compound and (ii) an acidic compound is used.
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Page/Page column 4
(2009/01/24)
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- Nucleophilic substitution reactions of sulfur-substituted cyclohexanone acetals: An analysis of the factors controlling stereoselectivity
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The reactions of cyclohexanone acetals substituted with thiophenyl groups (and other heteroatoms) at C-2 demonstrate the powerful influence that these substituents have on the stereoselectivity of nucleophilic substitution reactions. The trans selectivities of these reactions correlate with the behavior of the corresponding ketones. These experiments lend support to the possibility that the reactions of the acetals, which proceed via oxocarbenium ions, are operating under Felkin-Anh control.
- Billings, Susan B.,Woerpel
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p. 5171 - 5178
(2007/10/03)
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- First lipase catalysed resolution of epoxy enol esters
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We report the first enzyme-catalysed kinetic resolution of epoxy enol esters. The lipase-promoted hydrolysis of these compounds provided α-hydroxyketones or α-hydroxyaldehydes (arising from the spontaneous rearrangement of the epoxy enols) and the residual esters with moderate to good enantioselectivity (E up to 100).
- Gravil, Sébastien,Veschambre, Henri,Chênevert, Robert,Bolte, Jean
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p. 6153 - 6157
(2007/10/03)
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- Elimination-addition mechanism for nucleophilic substitution reaction of cyclohexenyl iodonium salts and regioselectivity of nucleophilic addition to the cyclohexyne intermediate
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The reaction of 4-substituted cyclohex-1-enyl(phenyl)iodonium tetrafluoroborate with tetrabutyl-ammonium acetate gives both the ipso and cine acetate-substitution products in aprotic solvents. The isomeric 5-substituted iodonium salt also gives the same mixture of the isomeric acetate products. The reaction is best explained by an elimination-addition mechanism with 4-substituted cyclohexyne as a common intermediate. The cyclohexyne formation was confirmed by deuterium labeling and trapping to lead to [4 + 2] cycloadducts and a platinum-cyclohexyne complex. Cyclohexyne can also be generated in the presence of some other mild bases such as fluoride ion, alkoxides, and amines, though amines are less effective bases for the elimination. Kinetic deuterium isotope effects show that the anionic bases induce the E2 elimination (k H/kD > 2), while the amines allow formation of a cyclohexenyl cation in chloroform to lead to E1 as well as SN1 reactions (k H/kD ≈ 1). Bases are much less effective in methanol, and methoxide was the only base to efficiently afford the cyclohexyne intermediate. Nucleophiles react with the cyclohexyne to give regioisomeric products in the ratio dependent on the ring substituent. The observed regioselectivity of nucleophilic addition to substituted cyclohexynes is rationalized from calculated LUMO populations, which are governed by the bond angles at the acetylenic carbons: The less deformed carbon has a higher LUMO population and is preferentially attacked by the nucleophile.
- Fujita, Morifumi,Kim, Wan Hyeok,Sakanishi, Yuichi,Fujiwara, Koji,Hirayama, Sayaka,Okuyama, Tadashi,Ohki, Yasuhiro,Tatsumi, Kazuyuki,Yoshioka, Yasunori
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p. 7548 - 7558
(2007/10/03)
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- Catalytic enantioselective synthesis of α-aminooxy and α-hydroxy ketone using nitrosobenzene
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The highly enantioselective and O-selective nitroso aldol reaction of tin enolates 2 and nitrosobenzene (1) has been developed with the use of (R)-BINAP-silver complexes as a catalyst. After the various silver salts were surveyed, the AgOTf and the AgClO4 complex were found to be optimal in the O-selective nitroso aldol reaction in both asymmetric induction (up to 97% ee) and regioselection (O/N = >99/1), affording aminooxy ketone 3. The product 3 can be transformed to α-hydroxy ketone 5 without any loss of enantioselectivity. Thus, the method provides an efficient approach to the catalytic enantioselective introduction of oxygen α- to the carbonyl group. Copyright
- Momiyama, Norie,Yamamoto, Hisashi
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p. 6038 - 6039
(2007/10/03)
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- Practical and User-Friendly Procedure for Michael Reactions of α-Nitroketones in Water
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A variety of α,β-unsaturated carbonyl derivatives gave selective Michael additions with several α-nitrocycloalkanones in water, at room temperature without any added catalyst, or in very dilute, aqueous solutions of potassium carbonate. Both preparative methods constitute new, environmentally benign and more efficient alternatives to previous procedures.
- Miranda, Sonia,López-Alvarado, Pilar,Giorgi, Giorgio,Rodriguez, Jean,Avenda?o, Carmen,Menéndez, J. Carlos
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p. 2159 - 2162
(2007/10/03)
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- A practical and efficient synthetic route to dihydropipercide and pipercide
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Dihydropipercide 1 and Pipercide 2 are examples of hydrophobic insecticidal isobutylamide derivatives isolated from Piper Nigrum L. which have received synthetic attention over the past decade. Novel structural features combining the N-isobutyldieneamide array, found in related natural products such as Pellitorine, with the 3,4-methylenedioxyphenyl moiety, found in insecticide synergists including Piperonyl Butoxide and Sesamex, render these as attractive targets for synthesis. Although a variety of synthetic routes to related natural products have appeared in the literature, practical methods for the preparation of the title compounds were lacking. Convenient and convergent 10-11-step protocols were developed which provided access to gram quantities of the targets. Methyl 6-oxohexanoate 4 was prepared from cyclohexanone enol acetate 3 via a tandem ozonolysis, methanolysis, hydrolysis process. Subsequent olefination and olefin isomerization steps followed by further elaboration provided the targets 1 and 2. Noteworthy features of this methodology include the convenient synthesis of oxoester intermediate 4 and the phenythio radical-induced olefin isomerization of intermediate 6 which afforded high yields of >99.5% E-olefin 13. These are both somewhat uncommon but potentially useful processes which may find further application in organic synthesis.
- Rotherham, Lloyd W.,Edward Semple
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p. 6667 - 6672
(2007/10/03)
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- Selective O-acylation of silyl enol ethers with acid halides mediated by a copper(I) salt
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A new selective synthetic method of enol esters (O-acylated products) from silyl enol ether and acid chloride in the presence of CuCl is described. This reaction proceeds smoothly in DMI (1,3-dimethyl-2-imidazolidinone) but not in a less polar solvent. The silicon-copper exchange reaction pathway is proposed for this transformation as in the cases of D and alkynylsilane which were previously reported.
- Ito, Hajime,Ishizuka, Tomoko,Tateiwa, Jun-Ichi,Hosomi, Akira
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p. 6295 - 6298
(2007/10/03)
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- PALLADIUM CATALYZED INDIRECT ELECTROCHEMICAL ACETOXYLATION OF OLEFINS
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Olefins are acetoxylated to allylic and vinylic unsaturated esters by palladium (II) acetate catalyst in combination with controlled current anodic reoxidation and copper (II) acetate as an electron transfer agent.
- Hartstock, Frederick W.,Wayner, Danial, D. M.
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p. 8137 - 8140
(2007/10/02)
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- Facile reductive dimerisation of aryl ketones using Zn-Ac2O
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A simple reductive dimerisation of aryl ketones by zinc-acetic anhydride, resulting in the formation of pinacolones and related compounds is reported.
- Nair, C. K. Snehalatha,Krishnakumari, B.,Pardhasaradhi, M.
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p. 540 - 542
(2007/10/02)
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- Vinyl Cation Formation by Decomposition of Vinyl-lead Triacetates. The Reactions of Vinylmercury and Vinyltin Compounds with Lead Tetra-acetate
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Vinylmercury compounds and vinylstannanes undergo rapid metal-metal exchange with lead tetra-acetate in chloroform to generate vinyl-lead triacetates, unstable compounds which undergo a thermodynamically favourable reductive elimination of lead(II) acetate.In the presence of mercury(II) salts, vinyl-lead triacetates collapse to the corresponding enol acetate, but in the absence of mercury(II) they yield either the enol acetate or an acetylene depending on the substitution at the double bond.Evidence for the formation of vinyl cations in the collapse of a number of vinyl-lead triacetates has been obtained.Strong support for such intermediates comes from the decomposition of (E)-o-methoxystyryl-lead triacetate, where the nature of the participation by the neighbouring methoxy group excluded the possibility of involvement of an alkylidenecarbene.Attempted trapping of an alkylidenecarbene by cyclohexane in the decomposition of 2-methylprop-1-enyl-lead triacetate was also unsuccessful, indicating the absence of such an intermediate.
- Moloney, Mark G.,Pinhey, John T.,Stoermer, Martin J.
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p. 2645 - 2655
(2007/10/02)
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- Oxidative Substitution Reactions of Organotin Compounds with Lead Tetra-acetate
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A new oxidative substitution reaction where an organotin group is replaced by an acetoxy group has been investigated; this reaction has been successfully applied to the synthesis of 4-ylidenebutenolides.
- Yamamoto, Makoto,Izukawa, Hiroyoshi,Saiki, Masaru,Yamada, Kazutoshi
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p. 560 - 561
(2007/10/02)
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- The Role of Vanadum(V) in the Oxidation of Cyclohexanol to Adipic Acid by Nitric Acid
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The oxidation of cyclohexanol to adipic acid by nitric acid takes place by two routes.One of these, in which 2-nitro-2-nitrosocyclohexanone (5) and the nitrolic acid (6) are intermediates, is not influenced by the presence of vanadium(V).The other, involving cyclohexane-1,2-dione (8) and its tautomer, only gives a significant amount of adipic acid if the metal ion is present.The dione and 'predione' (9), a dimeric species which can be isolated from the system, appear to be in equilibrium with the monohydrate (14).It is this last compound which is selectively oxidised by vanadium(V).The mono-enol (15) is formed by slow tautomerisation of dione and is selectively oxidised in the presence of vanadium(V) to glutaric acid.The mono-oxime (10) appears to be the key intermediate linking the two routes.
- Smith, J. R. Lindsay,Richards, D. I.,Thomas, C. B.,Whittaker, M.
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p. 1677 - 1682
(2007/10/02)
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- STEREOSELECTIVE ALDOL CONDENSATIONS OF ORGANOTIN REAGENTS WITH ALDEHYDES
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The reaction of the enolstannanes of cyclohexanone or propiophenone with various aldehydes under kinetic control (-78 deg C) gave predominately the threo aldols, diastereoselectivity as high as 95:5 being achived.At higher temperatures (+45 deg C) predominate erythro selectivity was observed.The enolstannane of propiophenone exists as an equilibrium mixture of O-Sn (probably the E-isomer) and C-Sn derivatives.Reaction at -78 deg C takes place rapidly with the O-Sn enolate, further reaction requiring isomerization of the C-Sn to the O-Sn enolate.The Pd catalyzed condensation of cyanomethyltributyltin with reactive aldehydes, such as nitrobenzaldehydes, took place at ambient temperatures in polar solvents to give high yields of condensation products.No reaction occured with aldehydes such as benzaldehyde.Only low stereoselectivity (10-34percent ee) was observed when (-)DIOP or (-)BPPM were utilized as chiral phosphine ligands.
- Labadie, Sharada S.,Stille, J. K.
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p. 2329 - 2336
(2007/10/02)
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- Arylation and 1-Alkenylation on α-Position of Ketones via Tributyltin Enolates Catalyzed by Palladium Complex
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The reaction of tributyltin enolates, prepared from tributyltin methoxide and enol acetates in situ, with aryl and 1-alkenyl bromides in the presence of dichlorobis(tri-o-tolylphosphine)palladium was found to give α-aryl and α-(1-alkenyl) ketones, respectively, in good yields with essentially complete retention of the enol acetate regiochemistry.
- Kosugi, Masanori,Hagiwara, Isao,Sumiya, Takao,Migita, Toshihiko
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p. 241 - 246
(2007/10/02)
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- Acylation of Ketone Silyl Enol Ethers with Acid Chlorides. Synthesis of 1,3-Diketones
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Trimethylsilyl enol ethers of ketones are acylated by a variety of acid chlorides in the presence of zinc chloride or antimony trichloride.The major product of this reaction is the 1,3-diketone resulting from C-acylation.Some O-acylation is observed in most cases.Yields of 1,3-diketones varied but were usually good to excellent.
- Tirpak, Robin E.,Rathke, Michael W.
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p. 5099 - 5102
(2007/10/02)
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- Amberlyst-15, an Effective Catalyst for Enol Acetylation
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Enol acetates of nine cyclic ketones have been prepared in high yields using Amberlyst-15 as catalyst.
- Patwardhan, S. A.
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p. 358 - 359
(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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