- Metal-free radical aromatic carbonylations mediated by weak bases
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We report a new method of metal-free alkoxycarbonylation. This reaction involves the generation of aryl radicals from arenediazonium salts by a very weak base (HCO2Na) under mild conditions. Subsequent radical trapping with carbon monoxide and alcohols gives alkyl benzoates. The conditions (metal-free, 1 equiv. base, MeCN, r.t., 3 h) tolerate various functional groups (I, Br, Cl, CF3, SF5, NO2, ester). Mechanistic studies indicate the operation of a radical aromatic substitution mechanism.
- Koziakov, Denis,Jacobi Von Wangelin, Axel
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supporting information
p. 6715 - 6719
(2017/08/22)
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- An efficient method for the preparation of: Tert -butyl esters from benzyl cyanide and tert -butyl hydroperoxide under the metal free condition
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A novel protocol to synthesize tert-butyl esters from benzyl cyanides and tert-butyl hydroperoxide has been successfully achieved. In the presence of tert-butyl hydroperoxide, Csp3-H bond oxidation, C-CN bond cleavage and C-O bond formation proceeded smoothly in one pot under the metal-free condition.
- Chen, Xiuling,Li, Yan,Wu, Minghu,Guo, Haibing,Jiang, Longqiang,Wang, Jian,Sun, Shaofa
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p. 102023 - 102027
(2016/11/09)
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- A direct and sustainable synthesis of tertiary butyl esters enabled by flow microreactors
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Tertiary butyl esters find large applications in synthetic organic chemistry. A straightforward method for the direct introduction of the tert-butoxycarbonyl group into a variety of organic compounds has been developed using flow microreactor systems. The resultant flow process was more efficient, versatile and sustainable compared to the batch.
- Degennaro, Leonardo,Maggiulli, Daniela,Carlucci, Claudia,Fanelli, Flavio,Romanazzi, Giuseppe,Luisi, Renzo
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supporting information
p. 9554 - 9557
(2016/08/01)
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- A mesoporous organosilica grafted Pd catalyst (MOG-Pd) for efficient base free and phosphine free synthesis of tertiary butyl esters via tertiary-butoxycarbonylation of boronic acid derivatives without using carbon monoxide
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A mesoporous organosilica grafted palladium(ii) catalyst was synthesized and characterized using various spectroscopic techniques. Its catalytic activity was evaluated for the synthesis of tertiary butyl esters via tert-butoxycarbonylation of boronic acid
- Ghosh, Kajari,Molla, Rostam Ali,Iqubal, Md. Asif,Islam
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p. 3540 - 3551
(2015/06/25)
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- Copper-catalyzed oxidative esterification of aldehydes with dialkyl peroxides: Efficient synthesis of esters of tertiary alcohols
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Copper-catalyzed oxidative esterification of aldehydes with dialkyl peroxides has been developed. This protocol affords a novel approach for the synthesis of carboxylic esters of tertiary alcohols under mild conditions. Depending on the catalyst system, a variety of tertiary esters were produced in good to excellent yields.
- Zhu, Yefeng,Wei, Yunyang
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p. 13668 - 13670
(2013/08/23)
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- An efficient method for the preparation of tertiary esters by palladium-catalyzed alkoxycarbonylation of aryl bromides
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The palladium-catalyzed alkoxycarbonylation of aryl bromides is described for the efficient preparation of tertiary esters. The protocol proved compatible with a wide variety of functionalized (hetero)aromatic bromides, as well as several different sterically hindered tertiary alcohols, affording the alkoxycarbonylated products in high yields. Finally, the formation of aromatic trityl esters is discussed.
- Xin, Zhuo,Gogsig, Thomas M.,Lindhardt, Anders T.,Skrydstrup, Troels
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supporting information; experimental part
p. 284 - 287
(2012/02/16)
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- Involvement of adsorption effects in the TiO2-sensitized photooxidation rate of benzylic derivatives in CH3CN
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Competitive kinetic experiments in the TiO2-sensitized photooxidation of some series of differently ring-substituted benzylic derivatives (ArCHROR′) in aerated and/or deaerated CH3CN and in the presence of Ag2SO4 were carried out. From logkrel vs Ep plots it was hypothesized that a changeover of the electron abstraction site occurs on going from electron-donating to electron-withdrawing groups on the ring, from the aromatic moiety to the OCH3 group of benzyl methyl ethers, probably owing to the preferential adsorption of this group on TiO2 with respect to the aromatic ring. This phenomenon is not observed with benzyltrimethylsilanes because the orbital resulting from the overlap between the C-Si bond and the aromatic π system is the only adsorption site. The steric hindrance of an α-methyl group (in benzylic alcohols) or a tert-butyl group (in benzyl tert-butyl ethers) reduces the degree of adsorption but does not influence the shape of the plot because OR′ should still be the preferential adsorption group. This also provides useful information about the surface structure of TiO2 suspended in CH3CN. Copyright
- Del Giacco, Tiziana,Rol, Cesare,Sebastiani, Giovanni V.
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p. 127 - 132
(2007/10/03)
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- 'New' catalysts for the ester-interchange reaction: The role of alkali-metal alkoxide clusters in achieving unprecedented reaction rates
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The catalytic effect of alkali-metal tert-butoxide clusters on the rate of ester interchange for several pairs of esters has been determined in nonpolar and weakly polar solvents. Reactivities increase in the order (Li+ + + + +) with the fastest rates reaching 107 catalytic turnovers per hour (TO/h). Ester interchange rates were sensitive to the size of both the transferring OR groups and the ester substituent. Phenyl esters did not exchange with aliphatic esters due to nonstatistical breakdown patterns in the tetrahedral intermediate. A first-order equilibration analysis on the interchange between tert-butyl acetate (tBuAc) and methyl benzoate (MeBz) (5 mol % NaOtBu) indicated enhanced reaction rates as the reaction proceeded. Isolation and quenching (DCl/D2O) of precipitated catalyst points to a mechanism whereby sequential methoxy incorporation into the catalyst cluster increases activity, but eventually precipitates out of solution as a 3:1 OMe:OtBu cluster. The rate law was determined to be k(obs)[MeBz]1[tBuAc]0[NaOtBu](x), where x = 1.2(1), 1.4(1), and 0.85(1) in hexane, ether, and THF, respectively, under conditions where tetrameric catalyst aggregates are expected. Reaction rates were generally observed to be higher in nonpolar solvents (hexane > toluene, ether > THF). Eyring analysis over a 40°C range yielded ΔH(≠) = 10.0(1) kcal mol-1 and ΔS(≠) = -32(3) eu. A Hammett (σ) plot generated with para-substituted methyl benzoates gave ρ +2.35 (R 0.996). These results are interpreted in terms of a catalytic cycle composed of two coupled transesterification reactions with a turnover-limiting addition of a tert-butoxy-containing cluster (tetramer) to methyl benzoate. Catalyst relative reactivities (Cs+ > Rb+ > K+ > Na+ > Li+) are interpreted in terms of competitive electrostatic interactions between the alkali-metal and ground-state and transition-state anions. This analysis predicts the observed linear dependence between log(k(obs)) and l/r(ionic).
- Stanton, Matthew G.
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p. 5981 - 5989
(2007/10/03)
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- Dynamics of bond breaking in ion radicals. Mechanisms and reactivity in the reductive cleavage of carbon-fluorine bonds of fluoromethylarenes
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The reductive cleavage mechanism and reactivity of the carbon-fluorine bonds in fluoromethylarenes are investigated, in liquid ammonia and in DMF, by means of cyclic voltammetry and/or redox catalysis as a function of the number of fluorine atoms and of the structure of the aryl moiety. The reduction of the trifluoro compounds, eventually leading to complete defluorination, involves the di- and monofluoro derivatives as intermediates. Carbenes do not transpire along the reaction pathway. Application of the intramolecular dissociative electron transfer model allows the quantitative rationalization, in terms of driving force and intrinsic barrier, of the variation of the cleavage reactivity of the primary anion radical with the number of fluorine atoms and of the structure of the aryl moiety as well as with the solvating properties of the medium. When, related to the structural factors thus uncovered, the primary anion radical generates the di- and monofluoro intermediates far from the electrode surface, their reduction occurs homogeneously giving rise to an apparently direct six-electron process according to an internal redox catalysis mechanism. Conversely, with rapid cleavages, the reduction of the di- and monofluoro intermediates takes place at the electrode surface and the stepwise expulsion of the fluorides ions transpire in the cyclic voltammetric patterns.
- Andrieux, Claude P.,Combellas, Catherine,Kanoufi, Fredéric,Savéant, Jean-Michel,Thiébault, André
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p. 9527 - 9540
(2007/10/03)
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