- Solvent effects on the rate of the keto-enol interconversion of 2-nitrocyclohexanone
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The rates of tautomerization of 2-nitrocyclohexanone (2-NCH) have been measured spectrophotometrically at 25.0 ± 0.1 °C in several organic aprotic solvents and their binary mixtures. In cyclohexane the reaction is effectively catalyzed by bases and inhibi
- Siani, Gabriella,Angelini, Guido,De Maria, Paolo,Fontana, Antonella,Pierini, Marco
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supporting information; experimental part
p. 4236 - 4241
(2009/02/07)
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- Stereoselective alkylations of chiral nitro imine and nitro hydrazone dianions. Synthesis of enantiomerically enriched 3-substituted 1-nitrocyclohexenes
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(Chemical Equation Presented) Dianions of chiral nitro imines (generated by a combination of LDA and s-BuLi) underwent diastereoselective alkylation with methyl, butyl, isopropyl, allyl, and methallyl iodides. In contrast to the behavior of simple metalloenamines, the most selective auxiliary contained no coordinating groups but did possess a large steric difference between the two substituents. The yield and selectivity of the alkylations were improved by the addition of HMPA or DMPU. The use of (S)-1-naphthylethylamine as the auxiliary afforded the R absolute configuration of the alkylation products. This stereochemical outcome could be rationalized by simple steric approach controlled alkylation in a conformationally fixed, internally coordinated dianion. A SAMP nitro hydrazone gave poorer yields and selectivities.
- Denmark, Scott E.,Ares, Jeffrey J.
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scheme or table
p. 9647 - 9656
(2009/04/11)
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- Ionization and tautomerization of 2-nitrocyclohexanone in aqueous solution
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(Chemical Equation Presented) The keto-enol tautomerism of 2-nitrocyclohexanone (2-NCH) was studied in aqueous solution under different experimental conditions. Ketonization rate constants were measured spectrophotometrically at 25°C at an ionic strength of 0.4 mol dm -3 (NaCl) in diluted hydrochloric acid, in diluted sodium hydroxide, and in several buffers by using NaHSO3 as the scavenger of the keto form. A value of pKaEH = 4.78 for the enol form was obtained from the rate-pH profile of the reaction. A value of pK aKH = 5.97 for the keto form was directly obtained from the UV-vis spectra of 2-NCH recorded at different pHs. The equilibrium constant for the keto-enol tautomerism, pKT = -log([enol]/[ketone]) = 1.19, was obtained by combining the two pKa values (pKT = pKaKH - pKaEH). A comparison of these results with the corresponding values (Keefe, J. R.; Kresge, A. J. In The Chemistry of Enols; Rappoport, Z., Ed.; Wiley & Sons: New York, 1990; pp 399-480) for cyclohexanone shows the dramatic effects of an α-nitro substituent on the keto-enol acidities and the tautomerization constant of alicyclic ketones. Rates and equilibria were discussed in the light of the Bronsted equation, the principle of nonperfect synchronization, and the Marcus theory. It turns out that, on passing from nitroalkanes to nitroketones, the resonance contribution to pKa and deprotonation rate decreases, being overwhelmed by steric and inductive effects.
- Angelini, Guido,De Maria, Paolo,Fontana, Antonella,Pierini, Marco,Siani, Gabriella
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p. 4039 - 4047
(2008/02/04)
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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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- Method for preparing aromatic secondary amino compound
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Disclosed are (1) a method for preparing an aromatic secondary amino compound which comprises reacting an N-cyclohexylideneamino compound in the presence of a hydrogen moving catalyst and a hydrogen acceptor by the use of a sulfur-free polar solvent and/or a cocatalyst, and (2) a method for preparing an aromatic secondary amino compound which comprises reacting cyclohexanone or a nucleus-substituted cyclohexanone, an amine and a nitro compound corresponding to the amine in a sulfur-free polar solvent in the presence of a hydrogen moving catalyst, a cocatalyst being added or not added. In a further aspect, a method is provided for the preparation of aminodiphenylamine by reacting phenylenediamine and cyclohexanone in the presence of a hydrogen transfer catalyst in a sulfur-free polar solvent while using nitroaniline as a hydrogen acceptor.
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- α-nitration of ketones via enol silyl ethers. Radical cations as reactive intermediates in thermal and photochemical processes
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Highly colored (red) solutions of various enol silyl ethers and tetranitromethane (TNM) are readily bleached to afford good yields of α-nitro ketones in the dark at room temperature or below. Spectral analysis show the red colors to be associated with the intermolecular 1:1 electron donor-acceptor (EDA) complexes between the enol silyl ether and TNM. The formation of similar vividly colored EDA complexes with other electron acceptors (such as chloranil, tetracyanobenzene, tetracyanoquinodimethane, etc.) readily establish enol silyl ethers to be excellent electron donors. The deliberate irradiation of the diagnostic (red) charge-transfer absorption bands of the EDA complexes of enol silyl ethers and TNM at -40 °C affords directly the same α-nitro ketones, under conditions in which the thermal reaction is too slow to compete. A common pathway is discussed in which the electron transfer from the enol silyl ether (ESE) to TNM results in the radical ion triad [ESE?+, NO2?, C(NO2)3-]. A subsequent fast homolytic coupling of the cation radical of the enol silyl ether with NO2? leads to the α-nitro ketones. The use of time-resolved spectroscopy and the disparate behavior of theisomeric enol silyl ethers of α- and β-tetralones as well as of 2-methylcyclohexanone strongly support cation radicals (ESE?+) as the critical intermediate in thermal and photoinduced electron-transfer as described in Schemes 1 and 2, respectively.
- Rathore, Rajendra,Kochi, Jay K.
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p. 627 - 639
(2007/10/03)
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- A novel one pot synthesis of α-nitroketones from olefins using trimethylsilylnitrate-chromium trioxide reagent system
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A variety of α-nitroketones have been obtained from the corresponding olefins in good yields upon reaction with trimethylsilylnitrate-chromium trioxide reagent system.
- Reddy, M. Venkat Ram,Kumareswaran,Vankar, Yashwant D.
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p. 7149 - 7152
(2007/10/02)
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- Reactivity of 2-Substituted Cyclohex-1-enylacetic Acids with Diazodiphenylmethane in Various Alcohols
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The reactivities of 2-substituted cyclohex-1-enylacetic acids with diazodiphenylmethane in eleven alcohols has been investigated.The solvent effect is interpreted in terms of the influence of the relative permittivity on the rate constants.The multiple linear correlation of log k with the Kirkwood function of relative permittivity.Taft ?* value for the alkyl group of the alcohol and the number of γ-hydrogen atoms in the alcohol nγH was highly successful (R=0.9927).The log k values for the various acids were correlated by using the appropriate form of the extended Hammett equation involving inductive, resonance and steric parameters.The reaction of cyclohex-1-enylacetic acid with diazodiphenylmethane in eleven alcohols shows a good linear free energy relationship with the corresponding reaction of phenylacetic acid (R=0.9793).The results obtained for 2-substituted cyclohex-1-enylacetic acids were compared with the results for ortho-substituted phenylacetic acids under the same experimental conditions.
- Uscumlic, Gordana S.,Muskatirovic, Milan D.
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p. 1799 - 1802
(2007/10/02)
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- Facile Preparation of α-Nitroketones from Enol Silyl Ethers
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Treatment of enol silyl ethers with the mild nitrating agent tetranitromethane gives good yields of α-nitroketones at room temperature and below.
- Rathore, Rajendra,Lin, Zhe,Kochi, Jay K.
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p. 1859 - 1862
(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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- α-Nitro Ketones. 5. Synthesis of 2-Nitrocyclopentanones
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The synthesis of the trans-3-methyl-, trans-trans- and trans-cis-3,4-dimethyl-, trans-3,5,5-trimethyl-, and cis- and trans-5-methyl-2-nitrocyclopentanones was accomplished by nitration of substituted cyclopentanone enol acetates with nitric acid at 15 deg
- Elfehail. Fadia E.,Zajac, Walter W.
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p. 5151 - 5155
(2007/10/02)
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