- Conjugate addition of acetal-derived benzyl radicals generated from low-valent titanium-mediated CO bond cleavage
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A new method for the generation of benzyl radicals from acetals via low-valent titanium-mediated homolytic CO bond cleavage is presented. The low cost and availability of the developed titanium reagent enable efficient access to α-alkoxy carbon radical species via the developed reaction.
- Suga, Takuya,Nakamura, Masaharu,Takada, Ryusei,Ukaji, Yutaka
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supporting information
p. 1258 - 1260
(2021/05/17)
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- Practical acetalization and transacetalization of carbonyl compounds catalyzed by recyclable PVP-I
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A novel PVP-I catalyzed acetalizations/transacetalizations of carbonyl compounds has been developed processing with a mild and easy handling fashion. Different types of Acyclic and cyclic acetals were prepared from carbonyl compounds or their acetals successfully. Further applications of newly developed catalytic combination were testified. This protocol featured with simplicity of operation, mild reaction condition, short reaction time, recyclable of catalyst and broad substrates scope with excellent yields.
- Cao, Fu-Rong,Lu, Guangying,Ren, Jiangmeng,Wang, Di,Zeng, Bu-Bing
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- Photocatalytic Reductive Formation of α-Tertiary Ethers from Ketals
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A general photocatalytic reductive strategy for the construction of unsymmetrical α-tertiary dialkyl ethers is reported. By merging Lewis acid-mediated ketal activation and visible-light photocatalytic reduction, in situ-generated α-alkoxy radicals were found to engage in addition reactions with a variety of olefinic partners. Good reaction efficiency is demonstrated with a range of ketals of aromatic and aliphatic ketones. Extension to acetal substrates is also described, demonstrating the overall synthetic utility of this methodology for complex ether synthesis.
- Rossolini, Thomas,Ferko, Branislav,Dixon, Darren J.
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supporting information
p. 6668 - 6673
(2019/09/03)
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- Silver-Catalyzed Olefination of Acetals and Ketals with Diazoesters to β-Alkoxyacrylates
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The first silver-catalyzed reaction of acetals or ketals with diazoesters leading to trisubstituted or tetrasubstituted β-alkoxyacrylates is now reported. A broad range of acetals and ketals bearing different substituents is compatible with this protocol and thus provides an attractive approach for the synthesis of complex β-alkoxyacrylates. The power of this method was further demonstrated by the successful synthesis of picoxystrobin, which is one of the most popular agricultural fungicides commercialized by Dupont.
- Li, Jiawen,Qian, Bo,Huang, Hanmin
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supporting information
p. 7090 - 7094
(2018/11/23)
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- Dual-gold(I)-generated trifluoromethylation of terminal alkynes with Togni's reagent
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The interaction of a Au(I) catalyst (JohnPhosAu(I)-MeCN/SbF6) and the Togni's reagent 1, as a source of electrophilic trifluoromethyl group, has been studied in order to develop gold-catalysed alkyne trifluoromethylation reactions. Alkyne-CF3products were prepared in moderate yields (up to 46%) by electrophilic trifluoromethylation of terminal arylalkynes with Togni's reagent 1 in the presence of sub-stoichiometric amounts of gold catalyst (25%). The proposed addition-elimination reaction mechanism proceeds through a Au-Togni Reagent complex with a linear Togni Reagent-O-Au(I)-P-(phosphane) coordination mode (X-ray analysis). Alkyne deprotonation gives rapid formation of protonated Togni Reagent and a σ,π-acetylide dual-Au complex, confirmed by X-ray analysis. It was shown that the σ,π-dual-Au complex activates for trifluoromethylation, most likely by transfer of a [LAu]+fragment to the alkyne substrate. The resulting reactive π-Au+-alkyne intermediate probably undergoes O-/CF3-addition of Togni Reagent, and final elimination of Togni alcohol gives the alkyne-CF3product.
- Siah, Huey-San Melanie,Fiksdahl, Anne
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supporting information
p. 24 - 33
(2017/03/10)
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- Eco-friendly synthesis and antioxidant activity of new trifluoromethyl-substituted N-(pyrimidin-2-yl)benzo[d]thiazol-2-amines and some N-derivatives
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Abstract: A convenient and environmentally benign procedure for the synthesis of a new series of trifluoromethyl-substituted N-(pyrimidin-2-yl)benzo[d]thiazol-2-amines by the cyclocondensation reaction of (benzo[d]thiazolyl)guanidine with either 4-alkoxy-4-alkyl(aryl/heteroaryl)-1,1,1-trifluoroalk-3-en-2-ones or 2,2,2-trifluoro-1-(2-methoxycyclohexen-1-en-1-yl)ethanone is described. The main reactions were performed in refluxing water as the solvent (8–24?h), without catalysts, and the corresponding new N-(pyrimidinyl)-1H-(benzo[d]thiazolyl)amines were obtained at a 60–88?% yield. Subsequently, some di(hetero)arylamines were derivatized to the respective tertiary amines via easy N-alkylation and N-alkenylation reactions at 55–82?% yields. Finally, the Lipinski parameters and the total antioxidant activity of the new series of secondary arylamines were also evaluated. Graphical abstract: [Figure not available: see fulltext.]
- Bonacorso, Helio G.,Calheiro, Tainara P.,Rodrigues, Melissa B.,Stefanello, Sílvio T.,Soares, Félix A. A.,Zanatta, Nilo,Martins, Marcos A. P.
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p. 2185 - 2194
(2016/11/17)
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- Efficient syntheses of ethyl 2-methylthio-and ethyl 2-benzylthio-6-methyl(aryl)pyrimidine-4-carboxylates and their carboxylic acid derivatives
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A simple and efficient procedure for the synthesis of ethyl 2-methylthio-and ethyl 2-benzylthio-6-methyl(aryl)-pyrimidine-4-carboxylates and their corresponding acid derivatives is reported. The products are obtained in good yields via the cyclocondensation reaction of ethyl 4-alkoxy-2-oxo-4-methyl(aryl)-but-3-enoates with 2-methylisothiourea sulfate or 2-benzylisothiourea hydrochloride, under mild, basic, aqueous conditions.
- Zanatta, Nilo,Fortes, Andressa S.,Bencke, Carlos E.,Marangoni, Mário A.,Camargo, Adriano F.,Fantinel, Cassio A.,Bonacorso, Helio G.,Martins, Marcos A. P.
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p. 827 - 835
(2015/03/14)
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- Investigation of quantitative structure-reactivity relationships in the aliphatic Claisen rearrangement of bis-vinyl ethers reveals a dipolar, dissociative mechanism
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Kinetic investigations of substituent effects in the thermal rearrangement of bis-vinyl ether substrates are reported. Findings indicate that the influence of the various substituent patterns on the rate of rearrangement in these compounds differs from that documented in the literature for the analogous [3,3]-sigmatropic rearrangement of allyl vinyl ethers. In addition, the thermochemical data collected suggests the existence of a dissociative transition state with significant dipolar character. These findings provide a unique contribution to the already extensive body of literature dedicated to mechanistic investigation of the Claisen rearrangement of aliphatic allyl vinyl ethers.
- O'Rourke, Natasha F.,Wulff, Jeremy E.
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p. 1292 - 1308
(2014/03/21)
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- Anodic cleavage of several ketone N-phenylsemicarbazones into methyl N-phenylcarbamate and the corresponding dimethyl acetals
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Several ketone N-phenylsemicarbazones were electrooxidized in the presence of potassium iodide and a base using methanol as the solvent to give nearly commensurate amounts of methyl N-phenylcarbamate and the corresponding dimethyl acetals. Continuous evolution of gaseous nitrogen was observed from the anolyte during the electrooxidation. The reactions were carried out under very mild reaction conditions and are presumed to proceed through a four-electron oxidation process, in which the iodide ion plays an important role as an electron carrier.
- Nishikawa, Shinnosuke,Yamamori, Haruki,Ohashi, Kousuke,Okimoto, Mitsuhiro,Hoshi, Masayuki,Yoshida, Takashi
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p. 1766 - 1771
(2013/05/21)
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- A novel approach to the practical synthesis of sulfides: An InBr 3-Et3SiH catalytic system promoted the direct reductive sulfidation of acetais with disulfides
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We have demonstrated a facile and direct synthesis of sulfide derivatives using acetais and ketals, derived, from aromatic/ conjugated, aldehydes and aromatic ketones, with disulfides and the InBr3-Et3SiH reducing system., We also succeeded in developing an unprecedented one-pot preparation of an aliphatic sulfide from a disulfide and an aliphatic acetal. (Wiley-VCH Verlag GmbH & Co. KGaA.
- Sakai, Norio,Moritaka, Kohei,Konakahara, Takeo
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supporting information; experimental part
p. 4123 - 4127
(2009/12/09)
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- Pd(II)-catalyzed conversion of styrene derivatives to acetals: Impact of (-)-sparteine on regioselectivity
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Pd[(-)-sparteine]Cl2 catalyzes the formation of dialkyl acetals from styrene derivatives with Markovnikov regioselectivity. The substrate scope of this reaction has been investigated, and initial mechanistic studies indicate that the reaction proceeds through an enol ether intermediate and a Pd-hydride.
- Balija, Amy M.,Stowers, Kara J.,Schultz, Mitchell J.,Sigman, Matthew S.
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p. 1121 - 1124
(2007/10/03)
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- Antimalarial activity of 4-(5-trifluoromethyl-1H-pyrazol-1-yl)-chloroquine analogues
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The antimalarial activity of chloroquine-pyrazole analogues, synthesized from the reaction of 1,1,1-trifluoro-4-methoxy-3-alken-2-ones with 4-hydrazino-7-chloroquinoline, has been evaluated in vitro against a chloroquine resistant Plasmodium falciparum clone. Parasite growth in the presence of the test drugs was measured by incorporation of [3H]hypoxanthine in comparison to controls with no drugs. All but one of the eight (4,5-dihydropyrazol-1-yl) chloroquine 2 derivatives tested showed a significant activity in vitro, thus, are a promising new class of antimalarials. The three most active ones were also tested in vivo against Plasmodium berghei in mice. However, the (pyrazol-1-yl) chloroquine 3 derivatives were mostly inactive, suggesting that the aromatic functionality of the pyrazole ring was critical.
- Cunico, Wilson,Cechinel, Cleber A.,Bonacorso, Helio G.,Martins, Marcos A. P.,Zanatta, Nilo,De Souza, Marcus V.N.,Freitas, Isabela O.,Soares, Rodrigo P. P.,Krettli, Antoniana U.
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p. 649 - 653
(2007/10/03)
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- Tri-n-butylstannyl chloride-sodium cyanoborohydride mediated regioselective reductive demethoxylation of alkyl methyl ketals
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A regioselective reductive demethoxylation of alkyl methyl ketals employing sodium cyanoborohydride in the presence of a catalytic amount of tri-n-butyltin chloride as Lewis acid is described.
- Srikrishna,Viswajanani
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p. 621 - 625
(2007/10/03)
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- A mild and simple procedure for the reductive cleavage of acetals and ketals
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A convenient, mild and simple procedure, employing sodium cyanoborohydride in the presence of either catalytic or stoichiometric amount of boron trifluoride etherate in dry THF, for the reductive cleavage of the acetals and ketals is described.
- Srikrishna, Adusumilli,Viswajanani, Ranganathan
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p. 3339 - 3344
(2007/10/02)
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- Hemiacetals of Acetophenone. Aromatic Substituent Effects in the H+- and General-base-catalysed Decomposition in Aqueous Solution
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We describe a double-mixing stopped-flow technique for the study of the acid- and base-catalysed breakdown of the unstable methyl hemiacetals of aryl-substituted acetophenones in aqueous solution.The approach takes advantage of the build-up of the hemiacetal during the H+-catalysed decomposition of the corresponding dimethyl acetal.Thus, mixing a weakly basic solution of acetal with excess acid provides a solution containing unchanged acetal, the acetophenone product of the hydrolysis and the hemiacetal intermediate.After a short period of time ( +-catalysed acetal and hemiacetal breakdown are in good agreement with literature data, but our analysis suggests a larger resonance effect component than previously assumed.The corresponding set of Hammett plots for base catalysis of hemiacetal breakdown reveals a relatively weak dependence of the catalytic constants on aromatic substitution, which appears to be inconsistent with much stronger dependences on substitution in the leaving alcohol.We propose a case of non-perfect synchronization or imbalance in the transition state where, in the breakdown direction in a class n mechanism, the degree of C-O bond breakage as measured by β1g is considerable, but the change in hybridization of the central carbon (sp3 -> sp2), as measured by ρ, lags behind in the transition state so that there is less interaction with the aromatic substituents here.
- McClelland, Robert A.,Engell, Karen M.,Larsen, Truels S.,Soerensen, Poul E.
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p. 2199 - 2206
(2007/10/02)
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- The Mechanism of Termal Eliminations. Part 26. Substituent Effects at Each Carbon of Vinyl Ethers: Non-planarity of the Transition State
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A range of 1-arylethyl vinyl ethers and 1-arylvinyl isopropyl ethers, 2-phenylethyl vinyl ether, isopropenyl isopropyl ether, and isopropyl cis- and trans-phenylvinyl ether have been synthesized and their rates of termal elimination measured between 585.9-666.4 K.The Ei mechanism for vinyl ether pyrolysis has less E1 character than that for pyrolysis of the corresponding esters, so nucleophilic attack by the double bond upon the β-hydrogen is more important for the former.Electron supply to the double bond therefore increases the pyrolysis rate, so that isopropenyl isopropyl ether is more reactive than isopropyl vinyl ether (5.85-fold at 600 K), whereas acetates and formates are almost equally reactive.Likewise isopropyl 1-phenylvinyl ether is 2.2 times more reactive than isopropenyl isopropyl ether,slightly greater than the reactivity difference between the corresponding esters (benzoates and acetates).The rate-enhancing effect of a 2--phenyl substituent in ethyl vinyl ether (5.81-fold per β-hydrogen) is a little less than the corresponding effect in ethyl acetate.In the 2-phenylvinyl ethers both cis and trans phenyl groups produce slight rate acceleration, due to the combined effects of loss of conjugation on going to products, and increase in electron supply to the double bond.The trans compound is more reactive than the cis, confirming that the six-membered transition state for β-elimination is not planar.Aryl substituents in 1-arylvinyl isopropyl ethers produce only very small rate effects; the effects could not be determined for electron-supplying substituents because these induced very rapid oxidation to isopropyl benzoates, and atmospheric hydrolysis also occurs.Isopropyl 2-phenylvinyl ethers were likewise oxidized to benzaldehyde and isopropyl formate. 1-Arylethyl vinyl ethers eliminate abnormally rapidly with concurrent rearrangements to aldehydes and other products.
- Taylor, Roger
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p. 737 - 744
(2007/10/02)
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- Kinetics and Mechanism of Acid-catalysed Addition of Methanol to α-Methoxystyrenes
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A kinetic study of the complex behaviour of ring-substituted α-methoxystyrenes in acidic (HBr) methanol is reported.The reaction yields the corresponding acetals as the only kinetic products; these are subsequently partly hydrolysed into acetophenones with rates only a little lower than those of their formation.The rate-limiting step for methanol addition corresponds to proton attachement to the double bond, yielding an oxocarbenium ion which is trapped by methanol with a rate constant 10E4 higher than that of ion deprotonation.The rate constants for proton transfer from CH3OH2+ are in the same range of magnitude as those for proton transfer from H3O+ in water.The lyonium ion catalytic constants fit a good Young-Jencks equation with ρn-2.86 and ρr-1.28
- Toullec, Jean,El-Alaoui, Mohiedine,Bertrand, Roland
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p. 1517 - 1522
(2007/10/02)
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- Kinetics and Mechanism of the Acid-Catalyzed Bromination of Ring-Substituted Acetophenones in Methanol. Thermodynamics of the Ketone-Acetal-Enol Ether System in Mathanol and Water
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The kinetics of HBr-catalyzed bromination of ring-substituted acetophenones in equilibrium with acetals have been studied in methanol containing small amounts of water at very low halogen concentration (ca. 10-6 M).Under these conditions, the rate is zeroth order with respect to the halogen and first order with respect to the CH3OH2+ ion and the overall carbonyl compound concentrations.The relative concentration of acetal at equilibrium (xeq = eq/(eq + eq)) has been varied by increasing the water concentration; the lyonium ion catalytic constant depends linearly on xeq with an xeq = 0 intercept corresponding to bromination via intermediate enol formation and with an xeq = 1 intercept corresponding to bromination via enol ether.In the case of 3-nitroacetophenone (1a), these extrapolated rate constants are identical with those directly measured from the rates for bromination of 1a and of 1a dimethyl acetal, before ketone-acetal equilibration.In most cases, the enol ether path is highly predominant.Substituent effects on the constants associated with the two paths are examined.The rate constants for enol ether formation are combined with rate constants for the reverse process and with acetal formation equilibrium constants to provide acetal-to-enol ether and ketone-to-enol ether equilibrium constants in methanol.Taking into account data of Gibbs free energies of transfer from methanol to water for the different species involved, equilibrium data in water are also deduced.
- Toullec, Jean,El-Alaoui, Mohiedine
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p. 4054 - 4061
(2007/10/02)
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- Ring Substituent Effects on Acetophenone Dimethyl Acetal Formation. 2. Dual-Parameter Treatment of Kinetic Data for Acid-Catalyzed Acetal Formation and Hydrolysis in Methanol Containing Small Amounts of Water
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The rates of formation and hydrolysis of para- and meta-substituted acetophenone dimethyl acetals have been measured, by a water-concentration method, in methanol containing HBr and small amounts of water.The rate coefficients for pure anhydrous methanol have been extrapolated .Acid and water-concentration effects are consistent with the usual mechanism for acetal hydrolysis in water, but the rate-limiting step in the hydrolysis direction corresponds to water addition to the hemiacetal-yielding oxocarbenium ion.Substituent effects on both extrapolated rate coefficients fit the Young-Jencks-modified Yukawa-Tsuno equation.The validity of this equation and its usefulness for separating polar and conjugative effects are discussed.
- Toullec, Jean,El-Alaoui, Mohiedine
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p. 4928 - 4933
(2007/10/02)
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- Solvolysis of α-Arylvinyl Ethyl Phosphates in Aqueous and Methanolic Solutions: Intramolecular Participation by the oxy Group
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The α-arylvinyl ethyl phosphates 2a-c were synthesized and their solvolysis reactions were studied in acidic aqueous solution and methanol.In aqueous solution both the anionic and neutral diesters are subject to acid-catalyzed hydrolysis.Solvent deuterium isotope effects, the observation of general acid catalysis by formic acid, and comparison with the reaction characteristics of the acid-catalized hydrolysis of other vinyl esters and ethers indicate that the anionic diesters hydrolyze via an ASE2 mechanism.The ratio of the rate constants for hydronium ion catalyzed hydrolysis of anionic and protonated 2c, k-/k0, is 14.1 +/- 0.3.This modest acceleration is consistent with weak electrostatic stabilization of the developping cation by the anionic site, although an inductive effect must also contribute.A previously reported correlation of log kH+ for a series of alkenes of the type R1R2C=CH2 with the sum of the ?P+ parameters for R1 and R2 and k- for 2a at 25 deg C were used to calculate a value of -0.52 for the ?P+ parameter of the anionic oxy group.The estimated ?P+ of the protonated group is -0.43.These parameters and direct comparisons of hydrolysis rates of 2a-c with the hydrolysis rates of the corresponding triesters 1a-c and the α-arylvinyl methyl ethers confirm that the oxy group, in both of its ionization states, is intermediate between a oxy group and an alkoxy group in its ability to stabilize a cation.The solvolysis of 2a-c in methanol/HCl proceeds via two routes.An HCl-catalyzed pathway has characteristics very similar to the acid-catalyzed hydrolysis reactions.Another path, the rate of which is independent of HCl concentration, apparently involves intramolecular general acid catalysis of methanolysis by the prot onated oxy group.Differences in the ionization caonstants of the diesters in the two solvents apparently account for the divergent solvolysis behavior.
- Novak, Michael,Roy, Kalpana R.
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p. 4584 - 4590
(2007/10/02)
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