- Medium-Ring Systems. 5. Synthesis and Base-Catalyzed Isomerizations of Medium-Ring Cycloalkenones with Electron-Withdrawing Substituents
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Medium-ring 3-cycloalkenones with electron-withdrawing substituents at the 3-position have been synthesized and subjected to base-catalyzed isomerizations.In a given ring size in the seven- and eight-membered carbocycles, the substituents studied caused similar shifts in the equilibria toward the 3-cycloalkenones relative to the unsubstituted cases.Steric effects of the substituents are therefore not significant.As the ring size is increased, the preference for the 3-cycloalkenone becomes more pronounced.In the nine- and ten-membered systems, an additional equilibrium involving formation of 4-cycloalkenones appears.Decreased effectiveness of conjugative interactions in endocyclic dienolates and in 2-cycloalkenones with increasing ring size is suggested.
- Mease, Ronnie C.,Hirsch, Jerry A.
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- Generating and optimizing the catalytic activity in UiO-66 for aerobic oxidation of alkenes by post-synthetic exchange Ti atoms combined with ligand substitution
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The catalytic activity for the aerobic epoxidation of cyclooctene of UiO-66 has been introduced by post-synthetic ion exchange of Zr4+ by Ti4+ at the nodes and the performance optimized by nitro substitution in the terephthalate ligand. In this way a TON value of 16,600 (1660 considering Zr + Ti content) was achieved, comparing favorably with the highest catalytic activity reported in homogeneous for the same reaction (10,000 for γ-SiW10{Fe3+(OH2)}2O386?). Kinetic studies have shown that the most likely reactive oxygen species involved in the oxidation is superoxide, with hydroxyl radicals also contributing to the reaction. UiO-66(Zr5.4 Ti0.6)-NO2 is stable under catalytic conditions, being used six times without any change in the conversion temporal profile and in the X-ray diffractogram. The scope of UiO-66(Zr5.4 Ti0.6)-NO2 promoted aerobic oxidation of alkenes was expanded by including smaller rings cycloalkenes, as well as acyclic and aryl conjugated alkenes.
- Santiago-Portillo, Andrea,Navalón, Sergio,álvaro, Mercedes,García, Hermenegildo
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- ENONE SYNTHESIS VIA α-PYRIDYLSELENO CARBONYL COMPOUNDS
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Oxidative elimination of α-pyridylseleno carbonyl compounds affords enones in excellent yields, providing an improved method for dehydrogenation of ketones and aldehydes.These results indicate that pyridylseleno group is a better leaving group than phenylseleno group in selenoxide elimination leading to enones.
- Toshimitsu, Akio,Owada, Hiroto,Uemura, Sakae,Okano, Masaya
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- Allylic oxidation of olefins with a manganese-based metal-organic framework
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Selective oxidation of olefins to α,β-unsaturated ketones under mild reaction conditions has attracted considerable interest, since α,β-unsaturated ketones can serve as synthetic precursors for various downstream chemical products. The major inherent challenges with this chemical oxidation are chemo- and regio-selectivity as well as environmental concerns, i.e. catalyst recycle, safety and cost. Using atmospheric oxygen as an environmentally friendly oxidant, we found that a metal-organic framework (MOF) constructed with Mn and a tetrazolate ligand (CPF-5) showed good activity and selectivity for the allylic oxidation of olefins to α,β-unsaturated ketones. Under the optimized conditions, we could achieve 98% conversion of cyclohexene and 87% selectivity toward cyclohexanone. The combination of a substoichiometric amount of TBHP (tert-butylhydroperoxide) and oxygen not only provides a cost effective oxidation system but significantly enhances the selectivity to α,β-unsaturated ketones, outperforming most reported oxidation methods. This catalytic system is heterogeneous in nature, and CPF-5 could be reused at least five times without a significant decrease in its catalytic activity and selectivity.
- Chen, Jingwen,Chen, Minda,Zhang, Biying,Nie, Renfeng,Huang, Ao,Goh, Tian Wei,Volkov, Alexander,Zhang, Zhiguo,Ren, Qilong,Huang, Wenyu
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- Enzymatic allylic oxidations with a lyophilisate of the edible fungus Pleurotus sapidus
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Allylic oxidations belong to the most attractive synthetic transformations because they convert readily available and cheap starting materials into value-added products. In this study, we describe oxidative conversions of terpenoids and a number of related cycloalkenes with a lyophilisate of the edible fungus Pleurotus sapidus. The biocatalytic protocol is simple and the biocatalyst is readily available. The conversions of various cycloalkenes proceed cleanly in most cases to the corresponding enones. The substrate scope is remarkable and includes a number of mono- and sequiterpenes, functionalized terpenoids as well as simple cyclohexenes and benzylic substrates. Enzymatic allylic oxidations by Pleurotus sapidus are thus an excellent non-toxic alternative to metal-mediated oxidation procedures in academic labs and for industrial application in food technology, cosmetics or pharmaceutical research. The Royal Society of Chemistry 2012.
- Rickert, Aljona,Krombach, Verena,Hamers, Oliver,Zorn, Holger,Maison, Wolfgang
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- Heterometallic CuII/LnIII polymers active in the catalytic aerobic oxidation of cycloalkenes under solvent-free conditions
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Heterometallic 3d-4f inorganic polymers were prepared using 3,5 pyridinedicarboxylic acid (H2PDC), {[CuLn2(PDC)2(SO4)2(H2O)6]·H2O}n (Ln: SmIII, CuSmPDC, EuIII, CuEuPDC, GdIII, and CuGdPDC). These catalysts are active in the aerobic oxidation of cycloalkenes under solvent-free conditions, with a conversion for the oxidation of cyclohexene of 71% after one hour of the reaction, and a TOF value of 1438 h-1 for CuSmPDC. On the other hand, the oxidation of cycloheptene and cyclooctene exhibited slightly lower conversions of 52% and 47%, and TOF values of 1053 and 159 h-1 after 1 and 6 hours of the reaction, respectively. The radical mechanism for the oxidation reaction of cyclohexene was assessed by Raman and EPR spectroscopy. The first evidenced the formation of Cu-O2 adducts and the second permitted is to observe the presence of the oxygen centered radical species, which act as initiators of the reaction chain to generate the products. An increase in the temperature of the reaction correlates with the adduct formation, and with the enhancement of the oxidation reaction.
- Cancino,Santiba?ez,Fuentealba,Olea,Vega,Spodine
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- PINO/NHPI-mediated selective oxidation of cycloalkenes to cycloalkenones: Via a photo-electrochemical method
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The selective photo-electrochemical oxidation of cyclohexene to 2-cyclohexene-1-one was successfully performed with excellent Faraday efficiency (>99%) via indirect oxidation with a PINO/NHPI mediator and O2 on a BiVO4/WO3 photoanode under low applied bias.
- Tateno, Hiroyuki,Miseki, Yugo,Sayama, Kazuhiro
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- OXIDATION OF ALKENES TO ENONES USING tert-BUTYL HYDROPEROXIDE IN THE PRESENCE OF CHROMIUM CARBONYL CATALYSTS
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Treatment of alkenes with t-butyl hydroperoxide in the presence of Cr(CO)6 or Cr(CO)x(CH3CN)y species results in oxidation of allylic methylene groups to give α,β-unsaturated ketones, selectively in the presence of certain alcohols, and in moderate to excellent yields.
- Pearson, Anthony J.,Chen, Yong-Shin,Hsu, Shih-Ying,Ray, Tapan
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- A new route to seven- and eight-membered carbocycles
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A facile method for the construction of bicyclo[6.3.0]undecane or bicycle[5.3.0]decane skeleton has been developed by the tandem application of the intramolecular Kulinkovich cyclopropanation of ω-vinyl esters and oxidation of the resulting cyclopropanols.
- U, Jong Sun,Lee, Jinhwa,Cha, Jin Kun
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- IBX in an ionic liquid: Eco-friendly oxidation of 17α- methylandrostan-3β,17β-diol, an intermediate in the synthesis of anabolic oxandrolone
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An easily available hypervalent iodine(V) reagent, 2-iodoxybenzoic acid (IBX) immobilized in the ionic liquid [bmim][Br] was found to be an efficient and eco-friendly protocol for the oxidation of 17α-methylandrostan- 3β,17β-diol (1). At ambient temperature oxidation of 1 with IBX gave mestanolone (2) in good yield and with an increased stoichiometric amount of IBX, oxidation adjacent to the carbonyl functionality (α,β- unsaturation) occurred to give dehydrogenated 17β-hydroxy-17α-methyl- Δ1-androsten-3-one (3) as the major product in a one-pot reaction. The product is easily obtained by extraction with diethyl ether and evaporation of the solvent.
- Chhikara, Bhupender S.,Chandra, Ramesh,Tandon, Vibha
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- Rate coefficients and products for gas-phase reactions of chlorine atoms with cyclic unsaturated hydrocarbons at 298 K
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Rate coefficients for the reaction of Cl atoms with cycloalkenes have been determined using the relative rate method, at 298 K and atmospheric pressure of N2. Reference molecule was n -hexane, and the concentrations of the organics were followed by gas chromatographic analysis. Cl atoms were prepared by photolysis of trichloroacetyl chloride at 254 nm. The relative rates of reactions of Cl atoms with cycloalkenes, with, respect to M-hexane, are measured as 1.12 ±0.38, 1.31 ±0.14, and 1.69±0.18forcyclopentene, cyclohexene, and cycloheptene, respectively. Considering the absolute value of the rate coefficient of the reaction of Cl atom with n-hexane as 3.03 ± 0.06 × 10-10 cm3 molecule-1 s -1, the rate coefficient values for cyclopentene, cyclohexene, and cycloheptene are calculated, to be (3.39 ± 1.08) × 10 -10, (3.97 ±0.43) × 10-10, and (5.12 ± 0.55) × 10-10 cm3 molecule-1 S -1', respectively. The experiments for each, molecule were repeated six to eight times, and the slopes and the rate coefficients given above are the average values of these measurements, and the quoted error includes 2σ as well as all other uncertainties in the measurement and calculations. The rate coefficient increases linearly with the number of carbon atoms, with an increment per additional CH2 group being (8.7 ± 1.6) × 11-12 cm3 molecule-1 s-1. Chloroketones and chloroalcohols, along with unsaturated, ketones and alcohols, were found to be the major products of Cl-atom-initiated oxidation of cycloalkenes in the presence of air. The atmospheric implications of these results are discussed, along with a comparison with the reported structure activity relationships.
- Sharma,Pushpa,Dhanya,Naik,Bajai
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- N-Hydroxyphthalimide Anchored on Diamond Nanoparticles as a Selective Heterogeneous Metal-free Oxidation Catalyst of Benzylic Hydrocarbons and Cyclic Alkenes by Molecular O2
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N-hydroxyphthalimide (NHPI) derived from trimellitic anhydride has been covalently anchored (4 wt %) through ester bonds to the surface of commercial diamond nanoparticles previously functionalized by chemical and thermal treatments (DH). IR spectroscopy of the NHPI/DH solid shows the presence of a characteristic peak at 1735 cm?1 attributable to the ester bond, while solid-state MAS 13C NMR spectroscopy shows two broad bands corresponding to carbon atoms of carbonyl groups (167 ppm) and aromatic carbons (127 ppm). NHPI/DH promotes autoxidation of isobutylbenzene involving superoxide (O2 .?) and hydroperoxide (HOO?) radicals; NHPI/DH can be reused at least three times and reach a minimum turnover number as high as 20 600, which is probably due to the inertness of the diamond surface, allowing free diffusion of reactive oxygen species. Analogous materials in which NHPI was anchored on activated carbon and multiwall carbon nanotubes were inefficient as autoxidation catalysts. NHPI/DH is able to promote also selective aerobic oxidation of other benzylic hydrocarbons and cycloalkenes.
- Blandez, Juan F.,Navalón, Sergio,álvaro, Mercedes,García, Hermenegildo
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- g-C3N4/metal halide perovskite composites as photocatalysts for singlet oxygen generation processes for the preparation of various oxidized synthons
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g-C3N4/metal halide perovskite composites were prepared and used for the first time as photocatalysts forin situ1O2generation to perform hetero Diels-Alder, ene and oxidation reactions with suitable dienes and alkenes. The standardized methodology was made applicable to a variety of olefinic substrates. The scope of the method is finely illustrated and the reactions afforded desymmetrized hydroxy-ketone derivatives, unsaturated ketones and epoxides. Some limitations were also observed, especially in the case of the alkene oxidations, and poor chemoselectivity was somewhere observed in this work which is the first application of MHP-based composites forin situ1O2generation. The experimental protocol can be used as a platform to further expand the knowledge and applicability of MHPs to organic reactions, since perovskites offer a rich variety of tuning strategies which may be explored to improve reaction yields and selectivities.
- Corti, Marco,Chiara, Rossella,Romani, Lidia,Mannucci, Barbara,Malavasi, Lorenzo,Quadrelli, Paolo
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p. 2292 - 2298
(2021/04/12)
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- METHOD FOR PRODUCING CYCLOALKENONE USING PHOTOELECTROCHEMICAL REACTION SYSTEM
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PROBLEM TO BE SOLVED: To provide a novel production method that can efficiently produce cycloalkenone with high selectivity by electrooxidation of cycloalkene. SOLUTION: The method includes a process in which: in an electrolyte containing cycloalkene, an imide compound and a supporting electrolyte, in the presence of molecular oxygen, a photoresponsive semiconductor metal oxide anode electrode is used to electro-oxidize cycloalkene under light irradiation. SELECTED DRAWING: Figure 3 COPYRIGHT: (C)2020,JPOandINPIT
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Paragraph 0047-0055; 0068-0070; 0075-0076
(2020/10/16)
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- Aerobic oxidation of the C-H bond under ambient conditions using highly dispersed Co over highly porous N-doped carbon
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Highly dispersed Co sites in highly porous N-doped carbon (Co-NC) were synthesized by high-temperature pyrolysis of Zn/Co bimetallic zeolitic imidazolate framework-8 (CoxZn100-x-ZIF). Wide characterization indicated that the pyrolysis atmosphere and temperature play crucial roles in the metal dispersion and pore structure of the resulting materials. A hydrogen treatment at elevated temperatures is found to favour the Zn volatilization and restrict the pore shrinkage of the ZIF precursor, thus yielding efficient catalysts with highly dispersed Co, a high surface area (1090 m2 g-1) and pore volume (0.89 cm3 g-1). When used as a catalyst for aerobic oxidation of ethylbenzene (EB), Co1Zn99-ZIF-800-H2 contributes to 98.9% EB conversion and 93.1% ketone selectivity under mild conditions (60 °C, 1 atm O2), which is 41.3 times more active in comparison to the ZIF-67-derived Co catalyst. Co-NC is stable and could be reused four times without obvious deactivation. This catalyst displays good chemoselectivity to the corresponding ketones when using a broad scope of hydrocarbon compounds.
- Nie, Renfeng,Chen, Jingwen,Chen, Minda,Qi, Zhiyuan,Goh, Tian-Wei,Ma, Tao,Zhou, Lin,Pei, Yuchen,Huang, Wenyu
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p. 1461 - 1466
(2019/03/26)
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- Influence of the channel size of isostructural 3d-4f MOFs on the catalytic aerobic oxidation of cycloalkenes
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The present work reports a new group of heterogeneous catalysts with a 3D structure, CuLnIDA, {[Cu3Ln2(IDA)6]·8H2O} (Ln: LaIII, GdIII or YbIII), with an organic linker (H2IDA: iminodiacetic acid). Different sets of O2 pressure and time were used in order to obtain the optimal reaction conditions at 75 °C. The reaction was found to depend on the [aldehyde]/[substrate] ratio. The best results, with a conversion of 73% for CuLaIDA as the catalyst, were obtained for the smallest ratio of 0.2. Finally, the importance of the pore size was analysed by comparing the catalytic activity of the as formed catalyst with that of the thermally activated one. The conversion increased ca. 26-35% for the different catalysts when they were previously activated. In addition, the selectivity increased towards cyclohexenone. The use of molecular oxygen as the oxidizing agent in a system where an auxiliary solvent is not used, as the cyclohexene substrate and products play the role of a solvent, permitted us to generate a more friendly environmental system for the oxidation of cycloalkenes under mild conditions.
- Cancino, Patricio,Santiba?ez, Luis,Stevens, Christian,Fuentealba, Pablo,Audebrand, Nathalie,Aravena, Daniel,Torres, Julia,Martinez, Sebastian,Kremer, Carlos,Spodine, Evgenia
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supporting information
p. 11057 - 11064
(2019/07/31)
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- IBX as a catalyst for dehydration of hydroperoxides: Green entry to α,β-unsaturated ketones: Via oxygenative allylic transposition
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A catalytic transformation of allylic hydroperoxides into α,β-unsaturated carbonyl compounds using IBX as a dehydration catalyst is described. The combination of a singlet oxygen ene reaction and the IBX-catalyzed dehydration provides α,β-unsaturated carbonyl compounds from alkenes via oxygenative allylic transposition with H2O as the only byproduct.
- Kuga, Tetsuya,Sasano, Yusuke,Iwabuchi, Yoshiharu
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supporting information
p. 798 - 801
(2018/02/06)
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- Cobalt-Catalyzed Regioselective Olefin Isomerization under Kinetic Control
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Olefin isomerization is a significant transformation in organic synthesis, which provides a convenient synthetic route for internal olefins and remote functionalization processes. The selectivity of an olefin isomerization process is often thermodynamically controlled. Thus, to achieve selectivity under kinetic control is very challenging. Herein, we report a novel cobalt-catalyzed regioselective olefin isomerization reaction. By taking the advantage of fine-tunable NNP-pincer ligand structures, this catalytic system features high kinetic control of regioselectivity. This mild catalytic system enables the isomerization of 1,1-disubstituted olefins bearing a wide range of functional groups in excellent yields and regioselectivity. The synthetic utility of this transformation was highlighted by the highly selective preparation of a key intermediate for the total synthesis of minfiensine. Moreover, a new strategy was developed to realize the selective monoisomerization of 1-alkenes to 2-alkenes dictated by installing substituents on the γ-position of the double bonds. Mechanistic studies supported that the in situ generated Co-H species underwent migratory insertion of double bond/β-H elimination sequence to afford the isomerization product. The less hindered olefin products were always preferred in this cobalt-catalyzed olefin isomerization due to an effective ligand control of the regioselectivity for the β-H elimination step.
- Liu, Xufang,Zhang, Wei,Wang, Yujie,Zhang, Ze-Xin,Jiao, Lei,Liu, Qiang
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p. 6873 - 6882
(2018/05/30)
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- Chiral-Substituted Poly-N-vinylpyrrolidinones and Bimetallic Nanoclusters in Catalytic Asymmetric Oxidation Reactions
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A new class of poly-N-vinylpyrrolidinones containing an asymmetric center at C5 of the pyrrolidinone ring were synthesized from l-amino acids. The polymers, particularly 17, were used to stabilize nanoclusters such as Pd/Au for the catalytic asymmetric oxidations of 1,3- and 1,2-cycloalkanediols and alkenes, and Cu/Au was used for C-H oxidation of cycloalkanes. It was found that the bulkier the C5 substituent in the pyrrolidinone ring, the greater the optical yields produced. Both oxidative kinetic resolution of (±)-1,3- and 1,2-trans-cycloalkanediols and desymmetrization of meso cis-diols took place with 0.15 mol % Pd/Au (3:1)-17 under oxygen atmosphere in water to give excellent chemical and optical yields of (S)-hydroxy ketones. Various alkenes were oxidized with 0.5 mol % Pd/Au (3:1)-17 under 30 psi of oxygen in water to give the dihydroxylated products in >93% ee. Oxidation of (R)-limonene at 25 °C occurred at the C-1,2-cyclic alkene function yielding (1S,2R,4R)-dihydroxylimonene 49 in 92% yield. Importantly, cycloalkanes were oxidized with 1 mol % Cu/Au (3:1)-17 and 30% H2O2 in acetonitrile to afford chiral ketones in very good to excellent chemical and optical yields. Alkene function was not oxidized under the reaction conditions. Mechanisms were proposed for the oxidation reactions, and observed stereo- and regio-chemistry were summarized.
- Hao, Bo,Gunaratna, Medha J.,Zhang, Man,Weerasekara, Sahani,Seiwald, Sarah N.,Nguyen, Vu T.,Meier, Alex,Hua, Duy H.
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p. 16839 - 16848
(2017/01/10)
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- Bismuth-substituted "sandwich" type polyoxometalate catalyst for activation of peroxide: Umpolung of the peroxo intermediate and change of chemoselectivity
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The epoxidation of alkenes with peroxides by WVI, MoVI, VV, and TiIV compounds is well established, and it is well accepted that the active intermediate peroxo species are electrophilic toward nucleophilic substrates. Polyoxotungstates, for example, those of the "sandwich" structure, [WZn(TM-L)2(ZnW9O34)2]q- in which TM = transition metal and L = H2O, have in the past been found to be excellent epoxidation catalysts. It has now been found that substituting the Lewis basic BiIII into the terminal position of the "sandwich" polyoxometalate structure to yield [Zn2BiIII2(ZnW9O34)2]14- leads to an apparent umpolung of the peroxo species and formation of a nucleophilic peroxo intermediate. There are two lines of evidence that support the formation of a reactive nucleophilic peroxo intermediate: (1) More electrophilic sulfoxides are more reactive than more nucleophilic sulfides, and (2) nonfunctionalized aliphatic alkenes and dienes showed ene type reactivity rather than epoxidation pointing toward "dark" formation of singlet oxygen from the nucleophilic intermediate peroxo species. Allylic alcohols reacted much faster than alkenes but showed chemoselectivity toward C-H bond activation of the alcohol and formation of aldehydes or ketones rather than epoxidation. This explained via alkoxide formation at the BiIII center followed by oxidative β-elimination.
- Amanchi, Srinivasa Rao,Khenkin, Alexander M.,Diskin-Posner, Yael,Neumann, Ronny
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p. 3336 - 3341
(2015/06/16)
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- Selective acceptorless dehydrogenation and hydrogenation by iridium catalysts enabling facile interconversion of glucocorticoids
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An iridium(III) pentamethylcyclopentadienyl catalyst supported by 6,6'-dihydroxy-2,2'-bipyridine displays exquisite selectivity in acceptorless alcohol dehydrogenation of cyclic α,β-unsaturated alcohols over benzylic and aliphatic alcohols under mild aqueous reaction conditions. Hydrogenation of aldehydes and ketones occurs indiscriminately using the same catalyst under hydrogen, although chemoselectivity could be achieved when other potentially reactive carbonyl groups present are sterically inaccessible. This chemistry was demonstrated in the reversible hydrogenation and dehydrogenation of the A ring of glucocorticoids, despite the presence of other alcohol/or carbonyl functionalities in rings C and D. NMR studies suggest that an iridium(III) hydride species is a key intermediate in both hydrogenation and dehydrogenation processes.
- Ngo, Anh H.,Adams, Michael J.,Do, Loi H.
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supporting information
p. 6742 - 6745
(2015/02/19)
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- Expanding the scope of biomass-derived chemicals through tandem reactions based on oxorhenium-catalyzed deoxydehydration
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New modes of DODH: Oxorhenium compounds act as deoxydehydration(DODH)/acid dual-purpose catalysts to transform biomass-derived diol substrates into a variety of commodity chemical precursors. The power of this approach is highlighted by a tandem [1,3]-OH shift/DODH of 2-ene-1,4-diols and 2,4-diene-1,6-diols, and by a DODH/esterification sequence of sugar acids to unsaturated esters for the production of polymers and plasticizers. Copyright
- Shiramizu, Mika,Toste, F. Dean
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p. 12905 - 12909
(2014/01/06)
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- Aerobic oxidation of cycloalkenes catalyzed by iron metal organic framework containing N-hydroxyphthalimide
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Iron metal organic framework [Fe(BTC)] loaded with N-hydroxyphthalimide (NHPI) promotes the aerobic oxidation of (cyclo)alkenes to give variable percentages of allylic oxidation products and the corresponding epoxide, dependidng on the nature of the substrate. In the case of cyclopentene and cyclohexene, aerobic oxidation catalyzed by NHPI/Fe(BTC) renders their corresponding unsaturated cyclic alcohol and ketone with 97% selectivity in 5 h at 6% and 12% conversion, respectively. Under the same experimental conditions, cyclooctene exhibited 95% selectivity toward the formation of cyclooctene oxide with 2% of cyclooctenol/one at 4 h. Cycloheptene as susbstrate exhibits an intermediate behavior, and the aerobic oxidation catalyzed by NHPI/Fe(BTC) leads to the formation of cycloheptenol/cycloheptenone with 77% selectivity, accompanied by 23% of cycloheptene oxide at 4 h. Further experiments with non-symmetric olefins exhibited also a mixture of products including epoxides and allyic products. A mechanism to explain these experimental results has been proposed.
- Dhakshinamoorthy, Amarajothi,Alvaro, Mercedes,Garcia, Hermenegildo
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experimental part
p. 259 - 265
(2012/06/01)
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- Palladium-catalyzed asymmetric alkylation in the synthesis of cyclopentanoid and cycloheptanoid core structures bearing all-carbon quaternary stereocenters
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General catalytic asymmetric routes toward cyclopentanoid and cycloheptanoid core structures embedded in numerous natural products have been developed. The central stereoselective transformation in our divergent strategies is the enantioselective decarboxylative alkylation of seven-membered β-ketoesters to form α-quaternary vinylogous esters. Recognition of the unusual reactivity of β-hydroxyketones resulting from the addition of hydride or organometallic reagents enabled divergent access to γ-quaternary acylcyclopentenes through a ring contraction pathway or γ-quaternary cycloheptenones through a carbonyl transposition pathway. Synthetic applications of these compounds were explored through the preparation of mono-, bi-, and tricyclic derivatives that can serve as valuable intermediates for the total synthesis of complex natural products. This work complements our previous work with cyclohexanoid systems.
- Hong, Allen Y.,Bennett, Nathan B.,Krout, Michael R.,Jensen, Thomas,Harned, Andrew M.,Stoltz, Brian M.
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p. 10234 - 10248
(2012/01/03)
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- Effective oxidation of benzylic and alkane C-H bonds catalyzed by sodium o-iodobenzenesulfonate with Oxone as a terminal oxidant under phase-transfer conditions
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Catalytic oxidation of benzylic C-H bonds could be efficiently realized using IBS as a catalyst which was generated in situ from the oxidation of sodium 2-iodobenzenesulfonate (1b) by Oxone in the presence of a phase-transfer catalyst, tetra-n-butylammonium hydrogen sulfate, in anhydrous acetonitrile at 60 °C. Various alkylbenzenes, including toluenes and ethylbenzenes, several oxygen-containing functionalities substituted alkylbenzenes, and a cyclic benzyl ether could be efficiently oxidized. And, the same reagent system of cat. 1b/Oxone/cat. n-Bu4NHSO4 could be applied to the effective oxidation of alkanes as well.
- Cui, Li-Qian,Liu, Kai,Zhang, Chi
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supporting information; experimental part
p. 2258 - 2265
(2011/05/08)
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- An efficient procedure for the TEMPO-catalyzed oxidation of alcohols to aldehydes and ketones using ferric chloride hexahydrate as terminal oxidant
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A simple, efficient procedure for the oxidation of alcohols by catalytic 2,2,6,6-tetramethyl-piperidyl-l-oxy (TEMPO) was developed using FeCl 3·6H2O as the terminal oxidant. The reaction gives high yield of the corresponding aldehydes and ketones with no over oxidation to the acid.
- Kumar, R. Senthil,Karthikeyan,Perumal, Paramasivan T.
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p. 720 - 725
(2008/09/21)
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- An efficient and general approach to β-functionalized ketones
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Figure presented The oxidation of selected anlons (N3 -, SCN-, I-, and Br-) by eeric ammonium nitrate (CAN) in the presence of substituted cyclopropyl alcohols provides a novel approach to β-functionalized ketones. The protocol has a number of advantages including short reaction times, ease of reagent handling, and mild, neutral reaction conditions. Overall, this method provides an alternative pathway to important starting materials and intermediates in organic synthesis.
- Jingliang, Jiao,Nguyen, Larry X.,Patterson, Dennis R.,Flowers II, Robert A.
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p. 1323 - 1326
(2008/01/01)
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- Copper-catalyzed rearrangement of vinyl oxiranes
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A novel copper-catalyzed vinyl oxirane ring expansion protocol has been developed. A wide range of vinyl oxiranes can be rearranged to 2,5-dihydrofurans in excellent yields in the presence of electrophilic copper(II) acetylacetonate catalysts. Regioisomeric vinyl oxiranes can be converted to a single dihydrofuran product using these conditions. This method uses low catalyst loadings (0.5-5 mol %), has good tolerance of substitution patterns, and can be done in the absence of solvent. Copyright
- Batory, Lindsay A.,McInnis, Christine E.,Njardarson, Jon T.
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p. 16054 - 16055
(2007/10/03)
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- Pd(OH)2/C-mediated selective oxidation of silyl enol ethers by tert-butylhydroperoxide, a useful method for the conversion of ketones to α,β-enones or β-Silyloxy-α,β-enones
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(Chemical Equation Presented) Pd(OH)2-catalyzed oxidation of silyl enol ethers by t-BuOOH gives either β-silyloxy-α,β-enones or α,β-enones in good yields depending on the base used.
- Yu, Jin-Quan,Wu, Hai-Chen,Corey
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p. 1415 - 1417
(2007/10/03)
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- Oxidative Synthesis of α,β-Unsaturated Ketone from α-Iodo Ketone Using Peracid
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Oxidation of α-iodo ketone in CH2Cl2 using m-chloro-perbenzoic acid yields α,β-unsaturated ketone by β-H elimination in good yield. This reaction affords a new and convenient synthetic method for α,β-unsaturated ketone from α-iodo ketone.
- Horiuchi, C. Akira,Ji, Shun-Jun,Matsushita, Masatoshi,Chai, Wen
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p. 202 - 204
(2007/10/03)
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- Iodine(V) reagents in organic synthesis. Part 4. o-Iodoxybenzoic acid as a chemospecific tool for single electron transfer-based oxidation processes
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o-Iodoxybenzoic acid (IBX), a readily available hypervalent iodine(V) reagent, was found to be highly effective in carrying out oxidations adjacent to carbonyl functionalities (to form α, β-unsaturated carbonyl compounds) and at benzylic and related carbon centers (to form conjugated aromatic carbonyl systems). Mechanistic investigations led to the conclusion that these new reactions are initiated by single electron transfer (SET) from the substrate to IBX to form a radical cation which reacts further to give the final products. Fine-tuning of the reaction conditions allowed remarkably selective transformations within multifunctional substrates, elevating the status of this reagent to that of a highly useful and chemoselective oxidant.
- Nicolaou,Montagnon,Baran,Zhong
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p. 2245 - 2258
(2007/10/03)
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- Synthesis of α,β-unsaturated ketone from α-iodo ketone using photoirradiation
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Irradiation of α-iodo ketone in hexane under a nitrogen atmosphere with a high-pressure mercury lamp (λ>300nm) at room temperature afforded the corresponding α,β-unsaturated ketones in good yield. This reaction affords a new, clean and convenient synthetic method for the α,β-unsaturated ketone.
- Ji, Shun-Jun,Takahashi, Eiji,Takahashi, T. Tomoyoshi,Horiuchi, C. Akira
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p. 9263 - 9266
(2007/10/03)
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- Steric and electronic effects in the diastereoselective catalytic epoxidation of cyclic allylic alcohols with methyltrioxorhenium (MTO)
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The steric effects of allylic substituents in the epoxidations with methyltrioxorhenium/urea/hydrogen peroxide adduct (MTO/UHP) have been assessed for a series of 3-alkyl-substituted cyclohexenes. The trans selectivity increases with the size of the substituent and the diastereoselectivities follow an excellent linear correlation with the steric substituent constants of Taft (E(s)) or Charton (v). Good cis selectivity is observed in the epoxidation of the cyclic allylic alcohols 2-cyclopentenol and 2-cyclohexenol due to a hydroxy-directing effect through hydrogen bonding; however, for 2-cycloheptenol and 2-cyclooctenol hydrogen bonding is ineffective and steric interactions cause a higher trans selectivity. The conformationally fixed cis- and trans-5-tert-butyl-2-cyclohexenols serve as suitable substrates for gauging the dihedral angle of the transition states for the oxygen transfer in these epoxidations. Thus, the MTO/UHP oxidant favours a quasi-equatorial arrangement of the hydroxy group for effective hydrogen bonding (hydroxy-group directivity), in analogy to m- chloroperbenzoic acid (m-CPBA) and dimethyldioxirane (DMD), and a dihedral angle of ca. 130°is suggested.
- Adam, Waldemar,Mitchell, Catherine M.,Saha-Moeller, Chantu R.
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p. 785 - 790
(2007/10/03)
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- Tetrachlorocyclopentadienone O-Oxide, a Facile Oxygen-Atom-Transfer Reagent: The Disproportionation of Cycloalkyldioxyl Radicals
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Photolysis of tetrachlorodiazocyclopentadiene (1) in oxygen-saturated hydrocarbon solvents results in the transient formation of tetrachlorocyclopentadienone O-oxide (3). This rapidly decomposes, giving rise to products derived from oxidation of the hydrocarbons. Cyclopentane, cyclopentene, cycloheptane, cycloheptene, cycloheptatriene, and indene have been studied. Cycloheptatriene and indene gave only low yields of tractable products, but the others gave the corresponding ketones and secondary alcohols as the major products. Although yields varied considerably, the ketone and alcohol products were always obtained, within experimental error, in a 1 : 1 molar ratio. This observed product ratio supports the disproportionation of cycloalkyldioxyl radicals as a crucial step.
- Dunkin, Ian R.,McCluskey, Adam
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p. 1397 - 1400
(2007/10/03)
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- Applications of the β-azidonation reaction to organic synthesis. α,β- Enones, conjugate addition, and γ-lactam annulation
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The β-azido functionalization reaction provides a mechanistically different enone synthesis that involves treatment of 2 with fluoride anion to effect desilylation and concomitant β-elimination to give 3. Table 1 lists a number of examples of the direct conversion of a TIPS enol ether into the corresponding α,β-enone via a β-azido TIPS enol ether. The β-azido group can be ionized with Me3Al or Me2AlCl and the intermediate enonium ion trapped by a variety of nucleophiles such as an allylstannane, electron-rich aromatics, TMS enol ethers, Et2AlCN, Me2AlCCR, Me4AlLi, and vinylaluminum reagents to give the products listed in Table 2. The diastereoselectivity of the reaction of a 4-substituted enonium ion with indole shows an unusual increase of selectivity with increasing temperature. Reduction of the azide 2 provides access to β-amino TIPS enol ethers 5, which, for example, can be converted into a cinnamide derivative and cyclized via a putative 'ene' process into a γ-lactam.
- Magnus, Philip
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p. 12486 - 12499
(2007/10/03)
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- A versatile cobalt(II)-Schiff base catalyzed oxidation of organic substrates with dioxygen: Scope and mechanism
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Cobalt(II) complex 1a-f derived from Schiff bases act as efficient catalysts during the oxidation of wide range of organic substrates(e.g. alkenes, alcohols, benzylic compounds and aliphatic hydrocarbons) with dioxygen in the presence of aliphatic aldehydes or ketones or ketoesters. EPR studies on 1a-f complexes suggest that the aliphatic carbonyl compounds promote the formation of a cobalt(II)-superoxo species responsible for the oxidation of organic compounds. These studies also demonstrate the role of ligands on cobalt in controlling the chemoselectivity of these oxidations. A plausible mechanistic rational is also provided for these oxidations.
- Punniyamurthy,Bhatia, Beena,Reddy, M. Madhava,Maikap, Golak C.,Iqbal, Javed
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p. 7649 - 7670
(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 electron transfer from enol silyl ethers to quinone. Part 2. Direct observation of ion-pair dynamics by time-resolved spectroscopy
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Time-resolved spectroscopy in two time domains (encompassing picoseconds and nanoseconds/microseconds) allows all the reactive intermediates involved in the photooxidation of enol silyl ethers (ESE) by chloranil (CA) to be identified, and each step in their temporal evolution to α-enone (E) and adduct (A) to be delineated.Thus, the radical-ion pair is the common intermediate formed in unit quantum yield via the highly efficient quenching of triplet chloranil by enol silyl ethers in both dichloromethane and acetonitrile.In the context of the Fuoss-Winstein formulation, the first-formed is a contact ion-pair, which in a non-polar solvent, such as dichloro-methane, predominantly suffers an initial ion-pair collapse (internal return) by β-proton transfer, and the resultant radical pair ultimately leads to α-enone (E).The contact ion-pair formed in the polar solvent undergoes diffusive separation, and the free ion ESE cation radical suffers desilylation by acetonitrile and ultimately leads to adduct (A).Added electrolyte to dichloromethane solutions modulates the ion-pair behaviour via the 'special salt effect' to divert the enone pathway to adduct formation.
- Bockman, T. Michael,Kochi, Jay K.
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p. 1633 - 1644
(2007/10/03)
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- Recoverable chiral sulfoxides for asymmetric synthesis: application to stereoselective carbonyl reduction and the asymmetric synthesis of allylic alcohols
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The enantiomerically pure cyclic sulfinamide S(S)R-(+)-3 reacts with the sodium enolates of ketones to give the corresponding homochiral sulfoxides.Reduction of the carbonyl group in these products may be achieved using a variety of reducing agents the best of which were DIBAL-H or DIBAL-H/ZnBr2, which give complementary products of high diastereomeric excess.Reduction of the hydroxy sulfoxides with Raney nickel proceeds in low yield and causes partial racemisation of the products.However the combined use of a durected reduction followed by a facile sulfenic acid elimination provides a synthesis of allylic alcohols in high enentiomeric excess.
- Butlin, Roger J.,Linney, Ian D.,Mahon, Mary F.,Tye, Heather,Wills, Martin
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- Synthesis of dioxochromium(VI) complexes, potential oxidation catalysts
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Some new chromium(VI) complexes have been synthesised using a number of tridentate and tetradentate ligands.Catalytic behaviour of one representative dioxochromium complex has been investigated in various oxidation reactions using 70percent t-butylhydroperoxide as oxidant.
- Agarwal, D. D.,Raina, Daisy,Agarwal, S. C.,Kaul, Anju
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p. 288 - 291
(2007/10/03)
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- Chromium pillared clay catalysed allylic oxidation and oxidative deprotection of allyl ethers and amines : A simple and convenient procedure
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An efficient method for allylic oxidation of cyclic and acyclic alkenes to the corresponding α,β-unsaturated carbonyl compounds in good yields was described using catalytic amounts of chromiapillared montmorillonite and equimolar quantities of tert-butyl hydroperoxide. This is also a convenient method for selective oxidative deprotection of allyl ethers and amines using same system. Incidentally this is the first heterogeneous system for the allylic oxidation as well as oxidative deprotection.
- Choudary, Boyapati M.,Prasad, Annavajhula Durga,Swapna, Vinukonda,Valli, Velaga L. K.,Bhuma, Vedantam
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p. 953 - 962
(2007/10/02)
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- New Trialkylsilyl Enol Ether Chemistry: New Regiospecific Methodology for the Synthesis of α,β-Unsaturated Cyclic Ketones
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Treatment of TIPS enol ethers with PhIO/TMSN3 followed by desilylation/elimination with fluoride ion gives good yields of the α,β-unsaturated ketone.
- Magnus, Philip,Evans, Andrew,Lacour, Jerome
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p. 2933 - 2936
(2007/10/02)
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- Methods for the introduction of a Phenylselenium Dichloride Group into he α-position of Carbonyl Compounds. Syntheses of Enones.
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Phenylselenium trichloride, PhSeCl3, direcly introduced, in fair yield, a PhSeCl2 group into the α-position of ketones with loss of HCl.To some extent, depending on the substrate, this reagent was also shown to act as a chlorinating agent toward ketones, yielding α-chloro ketones and α-phenylselenenyl ketones.The latter compounds were readily converted to selenium(IV) dichlorides by SO2Cl2 chlorination to significantly improve the overall yields of the selenetion process.The consecutive treatment of ketones with PhSeCl and SO2Cl2 could also be used for the introduction of a PhSeCl2 group, but this procedure was usually less efficient than the PhSeCl3-based one.Unsymmetrical ketones were selenated with poor regiocontrol.Aldehydes were primarily chlorinated by treatment with PhSeCl3, but consecutive treatment with PhSeCl3 and SO2Cl2 introduced a PhSeCl2 group into the α-position.Carboxylic acids and esters were ureactive toward PhSeCl3 and PhSeCl.PhSeCl3 underwent addition reactions with enones to introduce a PhSeCl2 group α or β to the carbonyl group, depending on the substrate.The carbonyl compounds substituted in the α-position with a PhSeCl2 group were easily converted to the corresponding α,β-unsaturated carbonyl compounds after hydrolysis/selenoxide elimination.Since the selenium(IV) intermediates involved were highly crustalline and easy to purify, the preparation of enones from symmetrical ketones via PhSeCl2 introduction/hydrolytic elimination was especially convenient to perform from the operational point of view.
- Engman Lars
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p. 4031 - 4037
(2007/10/02)
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- Reaction of FeCl3 with 7-chloro-1-silyloxybicycloheptanes : A way to 2-(1-chloroalkylidene)cyclohexanones.
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The regioselectivity of the FeCl3-promoted cleavage of the title compounds was studied : 2-(1,1-dichloroalkyl)cyclohexanones were obtained which were converted to 2-(1-chloroalkylidene)cyclohexanones by dehydrochlorination.
- Blanco, L.,Mansouri, A.
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p. 3239 - 3242
(2007/10/02)
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- NEW SYNTHETIC METHODS FOR α,β-UNSATURATED KETONES, ALDEHYDES, ESTERS AND LACTONES BY THE PALLADIUM-CATALYZED REACTIONS OF SILYL ENOL ETHERS, KETENE SILYL ACETALS, AND ENOL ACETATES WITH ALLYL CARBONATES
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Silyl enol ethers and ketene silyl acetals derived from ketones, aldehydes, esters and lactones are converted into α,β-unsaturated ketones, aldehydes and lactones by treatment with allyl carbonates in high yields using the palladium-bis(diphenylphosphino)ethane (dppe) complex as catalyst.Phosphine-free palladium catalyst instead of the palladium-phosphine complex gives a higher selectivity for the preparation of cyclopentenone, cyclooctenone, dienones, α,β-unsaturated esters and lactones.As a solvent, the use of nitriles such as acetonitrile is essential.In other solvents, allylation takes place.Enol acetates derived from ketones are converted into α,β-unsaturated ketones by reaction with allyl carbonate in acetonitrile using the palladium complex and tributyltin methoxide as bimetallic catalysts.
- Minami, Ichiro,Takahashi, Kazuhiko,Shimizu, Isao,Kimura, Tsuneo,Tsuji, Jiro
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p. 2971 - 2978
(2007/10/02)
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- PHENYL SELENIUM TRICHLORIDE IN SYNTHESIS. REACTION WITH KETONES. A NEW VARIATION OF THE SELENOXIDE ELIMINATION REACTION
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Phenyl selenium trichloride was used for the introduction of a PhSeCl2-group into the α-position of ketones.These products were converted to enones (hydrolysis/selenoxide elimination) or α-phenylselenoketones (thiourea-reduction).
- Engman, Lars
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p. 6385 - 6388
(2007/10/02)
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- A NEW Cr(VI) REAGENT FOR THE CATALYTIC OXIDATION OF SECONDARY ALCOHOLS TO KETONES
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A new process is described for the oxidation of secondary alcohols to ketones using peroxyacetic acid in the presence of a catalytic amount of 2,4-dimethylpentane-2,4-diol cyclic chromate.
- Corey, E. J.,Barrette, Ernie-Paul,Magriotis, Plato A.
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p. 5855 - 5858
(2007/10/02)
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