- Intermolecular domino Michael/aldol reactions of α,β-unsaturated esters, aromatic aldehydes, and various nucleophiles promoted with a catalytic amount of a guanidine base in DMSO
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In DMSO, a catalytic amount of Barton's base (2-t-butyl-1,1,3,3-tetramethylguanidine, BTMG) effectively catalyzed intermolecular three-component reactions of α,β-unsaturated esters, aldehydes, and carbon-, sulfur-, or nitrogen-pronucleophiles to give three-component addition products with the formation of two new σ-bonds: pronucleophiles and aldehydes reacted with α,β-unsaturated esters at their β-positions and α-positions, respectively. Mechanism studies suggested that these reactions proceeded by the first intermolecular Michael addition of anionic nucleophiles that were formed from pronucleophiles with a catalytic amount of BTMG, followed by intermolecular aldol reactions of transient ester enolates even in the presence of more than stoichiometric amounts of acidic pronucleophiles. High nucleophilicity over Br?nsted basicity of transient enolates in polar solvents was observed for transient ester enolates rather than ketone enolates.
- Matsuo, Jun-ichi,Morita, Shunya,Yoshimura, Tomoyuki
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- Poly(N-vinylimidazole) as efficient recyclable catalyst for the Michael addition of CH-acids to electron deficient alkenes in water
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Efficiency of poly(N-vinylimidazole) as the basic recyclable catalyst for the Michael addition of CH-acids to acrylonitrile, methyl acrylate, methyl vinyl ketone and methyl vinyl sulfone in water at ambient temperature was studied. In these reactions, formation of both 1 : 1 and 1 : 2 adducts is possible.
- Tarasenko, E. A.,Beletskaya, I. P.,Tyurin, V. S.,Lamaty, F.
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p. 2613 - 2616,4
(2020/09/16)
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- 2-Substituted nitrones and isomeric hydroxylamines - obtained via aluminium amalgam reduction of nitro nitriles and ketones-a new access to convenient intermediates for nitroso carbonyl compounds preparation
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Substituted five-membered cyclic nitrones (pyrroline N-oxides) have been obtained in good to high yields from tertiary γ-nitro ketones and nitriles employing aluminium amalgam as a reducing agent in moist diethyl ether or THF. Attempts to obtain cyclic amino nitrones from α- or β-nitro nitriles failed and only the corresponding hydroxylamines have been isolated. Both nitrones and hydroxylamines have been used for synthesis of tertiary C-nitroso nitriles or ketones.
- Grela, Karol,Konopski, Leszek
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body text
p. 3608 - 3613
(2010/07/05)
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- Bifunctional heterogeneous catalysis of silica-alumina-supported tertiary amines with controlled acid-base interactions for efficient 1,4-addition reactions
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We report the first tunable bifunctional surface of silica-aluminasupported tertiary amines (SA-NEt2) active for catalytic 1,4-addition reactions of nitroalkanes and thiols to electron-deficient alkenes. The 1,4-addition reaction of nitroalkanes to electron-deficient alkenes is one of the most useful carbon-carbon bond-forming reactions and applicable toward a wide range of organic syntheses. The reaction between nitroethane and methyl vinyl ketone scarcely proceeded with either SA or homogeneous amines, and a mixture of SA and amines showed very low catalytic activity. In addition, undesirable side reactions occurred in the case of a strong base like sodium ethoxide employed as a catalytic reagent. Only the present SA-supported amine (SA-NEt2) catalyst enabled selective formation of a double-alkylated product without promotions of side reactions such as an intramolecular cyclization reaction. The heterogeneous SA-NEt2 catalyst was easily recovered from the reaction mixture by simple filtration and reusable with retention of its catalytic activity and selectivity. Fur-thermore, the SA-NEt2 catalyst system was applicable to the addition reaction of other nitroalkanes and thiols to various electron-deficient alkenes. The solid-state magic-angle spinning (MAS) NMR spectroscopic analyses, including variable-contact-time 13C cross-polarization (CP)/MAS NMR spectroscopy, revealed that acid-base interactions between surface acid sites and immobilized amines can be controlled by pretreatment of SA at different temperatures. The catalytic activities for these addition reactions were strongly affected by the surface acid-base interactions. 2009 Wiley-VCH Verlag GmbH & Co. KGaA.
- Motokura, Ken,Tanaka, Satoka,Tada, Mizuki,Iwasawa, Yasuhiro
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experimental part
p. 10871 - 10879
(2010/04/05)
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- Oxalic acid catalyzed reaction between dithioacetals and acetals. A simple and eco-friendly method for a conversion of a dithioacetal to a carbonyl compound
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Oxalic acid catalyzes a reaction between dithioacetals and acetals. This reaction is useful in a new and eco-friendly method to convert dithioacetals to carbonyl compounds.
- Miyake, Hideyoshi,Nakao, Yuichi,Sasaki, Mitsuru
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p. 6247 - 6250
(2007/10/03)
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- Use of heterogeneous catalyst KG-60-NEt2 in Michael and Henry reactions involving nitroalkanes
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The N,N-diethylpropylamine supported on amorphous silica (KG-60-NEt2) catalyses the formation of carbon-carbon bonds by nitroalkanes through both the nitroaldol (Henry) and Michael reactions. The catalyst shows general utility with a variety of electrophilic acceptors. Moreover, the catalyst can be reused for two further cycles without loss of the activity.
- Ballini, Roberto,Bosica, Giovanna,Livi, Damiana,Palmieri, Alessandro,Maggi, Raimondo,Sartori, Giovanni
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p. 2271 - 2273
(2007/10/03)
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- P(RNCH2CH2)3N: Efficient 1,4-addition catalysts
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The 1,4-addition of primary alcohols, higher nitroalkanes, and a Schiff's base of an α-amino ester to α,β-unsaturated substrates produces the corresponding products in moderate to excellent yields when carried out at -63 to 70°C in the presence of catalytic amounts of the nonionic strong bases P(RNCH2CH2)3N (R = Me, i-Pr, i-Bu) in isobutyronitrile. Diastereoselectivity for the anti form of the product is high in the case of the Schiff's base in the absence of lithium ion. These catalysts are easily removed from the product by either column filtration through silica gel or via aqueous workup.
- Kisanga, Philip B.,Ilankumaran, Palanichamy,Fetterly, Brandon M.,Verkade, John G.
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p. 3555 - 3560
(2007/10/03)
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- Electrochemical and esr spin trap studies of a new iron tetra- catecholamide complex
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A new siderophore, N5,N6-thiodipropanoyl-bis[N1,N10-bis(2,3-dihydroxy benzoyl-spermidine)]-Fe (III) complex or H2LFe has been synthesised. The reaction of the reduced form of this complex with dioxygen has been investigated through electrochemical study and revealed the formation of a new species assumed to be H2O2. This species has been confirmed by esr spectroscopy using the diamagnetic compound 5-deutero-2,2,5- trimethylpyrrolidine-1-hydroxyl as spin trap. The resulting persistent radical is 5-deutero-2,2,5-trimethylpyrrolidine-1-yloxy (a(N) = 16.58 G, a(D) = 3.49 G).
- Cheraiti,Brik,Keita,Nadjo,Gaudemer
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p. 2315 - 2320
(2007/10/03)
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- The Michael reaction of nitroalkanes with conjugated enones in aqueous media
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The Michael reaction of various nitroalkanes with conjugated enones can be performed in NaOH 0.025 M and in the presence of cetyltrimethylammonium chloride (CTACl) as cationic surfactant, without any organic solvent. Good yields of the products are obtained even with hindered starting materials.
- Ballini, Roberto,Bosica, Giovanna
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p. 8027 - 8030
(2007/10/03)
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- New 2-Substituted Pyrroline-N-oxides: An EPR Solvent Study of the Radical Spin Adducts
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Ten substituted 5,5-dimethyl-1-pyrroline-N-oxides as well as the parent nitrene spin trap (DMPO) were prepared: 5,5-dimethyl-1-pyrroline-N-oxide, 2,5,5-trimethyl-1-pyrroline-N-oxide, 2-tert-butyl-5,5-dimethyl-1-pyrroline-N-oxide, 2-phenyl-5,5-dimethyl-1-pyrroline-N-oxide, 2-d5-phenyl-5,5-dimethyl-1-pyrroline-N-oxide, 2-phenyl-5,5-dimethyl-1-pyrroline-N-oxide-nitronyl-13C, 2-(4-fluorophenyl)-5,5-dimethyl-1-pyrroline-N-oxide, 2-(4-chlorophenyl)-5,5-dimethyl-1-pyrroline-N-oxide, 2-(4-tert-butylphenyl)-5,5-dimethyl-1-pyrroline-N-oxide, 2-(4-methylphenyl)-5,5-dimethyl-1-pyrroline-N-oxide and 2-(2-methylphenyl)-5,5-dimethyl-1-pyrroline-N-oxide.Analytical (i.e.EPR-grade) samples of these novel cyclic nitrones were obtained and characterized by (among other methods) 1H NMR spectroscopy.Reduction of DMPO and these various 2-substituted cyclic nitrones gave the corresponding cyclic N,N-dialkylhydroxylamines, whose structure and conformations were also analyzed by 1H NMR spectroscopy.Air oxidation of these cyclic N,N-dialkylhydroxylamines provided access to the EPR spectra of the hydrogen, methyl, tert-butyl, phenyl, d5-phenyl, nitronyl-13C-phenyl, 4-fluorophenyl, 4-chlorophenyl, 4-tert-butylphenyl, 4-methylphenyl and 2-methylphenyl cyclic aminoxyl (pyrrolidine N-oxyl nitroxide) radical spin adducts of DMPO.The 14N, 13C (where applicable) and 1H hyperfine splitting constants of these aminoxyl adducts in ten solvents of widely different polarities (e.g., hexane to water) were measured and the solvent effect on these parameters was evaluated.It was found that for the various 2-substituted DMPO-type apin adducts both the nitrogen and β-hydrogen EPR hyperfine splittings correlated linearly (r2 >/= 0.90) with typical solvent polarity parameters such as ET(30).The correlation between the nitrogen and β-hydrogen hyperfine splitting constants were even more linear (r2 >/= 0.97). - Keywords: electron paramagnetic resonance NMR 1H, 14N and 13C hyperfine splittings Spin traps Spin adducts Nitrones (1-pyrroline-N-oxides)
- Janzen, Edward G.,Zhang, Yong-Kang,Haire, D. Lawrence
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p. 711 - 720
(2007/10/02)
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- Mechanistic studies on the formation of aminoxyl radicals from 5,5-dimethyl-1-pyrroline-N-oxide in Fenton systems. Characterization of key precursors giving rise to background ESR signals
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To assign unidentified ESR signals obtained in a Fenton system with a spin trap, 5,5-dimethyl-pyrroline-N-oxide (DMPO), fundamental reactions of DMPO have been thoroughly investigated.When the concentration of Fe(2+) in Fenton systems exceeded 1percent of that of DMPO, background ESR signals totally distinguishable from 2-hydroxy-5,5-dimethyl-1-pyrollidinyloxy (DMPO-OH) appeared, and simultaneously absorbance at 520 nm increased, which was characteristic of hydroxamic acids complexed with Fe(3+).To prove the postulated formation of hydroxamic acid as a key intermediate, DMPO was subjected to Fenton reaction or was treated with Fe(3+) in aqueous solution to produce DMPO-OH (Makino et al.Biochem.Biophy.Res.Commun. 172, 1073 (1990)), and a major product was was isolated by RPLC.Based on (1)H, (13)C NMR and MS measurements, the structure of the major product was assigned to 1-hydroxy-5,5-dimethyl-1-pyrrolid-2-one (HDMPN) having a hydroxamic acid structure.Temperature dependence of NMR spectra and careful analysis of the fragmentation patterns in MS further revealed that HDMPN was present in equilibrium with 2-hydroxy-5,5-dimethyl-1-pyrroline-N-oxide (HDMPO), a tautomer of HDMPN.It has also been shown that the oxidation of DMPO yielding HDMPN and HDMPO occurs via DMPO-OH and is driven by Fe(3+).These oxidation products (HDMPN and HDMPO) were readily converted to the corresponding ESR visible aminoxyl radicals by oxidation and .OH addition in aqueous solution, respectively, and superimposition of the ESR signals arising from these radicals accounts for the background signals observed in Fenton systems with DMPO as spin trap.
- Makino, Keisuke,Hagi, Akifumi,Ide, Hiroshi,Murakami, Akira,Nishi, Masatoshi
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p. 2818 - 2827
(2007/10/02)
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- PALLADIUM CATALYZED C-ALLYLATION OF NITROALKANES
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A detailed study of palladium catalyzed C-allylation of aliphatic nitro compounds is described.Allylic alcohols and/or their acetates and allyl phenyl ethers were employed as allylating agents.The dependence of the reaction yield on nature and quantity of base and structure of the allylic unit is reported and explained.The lowest yield was obtained for allyl alcohol; however it could be considerably increased by addition of a stoichiometric amount of ethyl acetate.Order of reactivity of functional groups was OPh>OAc>OH.A novel method of synthesis of tetrakis (triphenylphosphine) palladium is also reported.
- Aleksandrowicz, Piotr,Piotrowska, Hanna,Sas, Wojciech
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p. 1321 - 1327
(2007/10/02)
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- Homosolvolysis
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Nitroxides, when used as solvents, promote the homolysis of a variety of weak bonds.Strong chemical evidence for the formation of free radicals is confirmed by e.s.r. studies in which the formation of free radicals has been monitored.This fission of single bonds of solute molecules dissolved in solvents with unpaired electrons is called homosolvolysis, in contrast to the common bond fission observed in polar solvents which is called heterosolvolysis.
- Scott, Alan C.,Tedder, John M.,Walton, John C.,Mhatre, Sushila
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p. 260 - 266
(2007/10/02)
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