- Discovery and characterization of a novel perylenephotoreductant for the activation of aryl halides
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To develop a photocatalyst with catalytical activity for substrates with low reactivities is always highly desired. Herein, based on the principle of structure–property relationships, we rationally designed the natural product cercosporin, the naturally occurring perylenequinonoid pigment, to develop a novel organic perylenephotoreductant, hexacetyl reduced cercosporin (HARCP), through structural manipulation. Compared with cercosporin, HARCP shows prominent electrochemical and photophysical characteristics with greatly improved photoreductive activity, fluorescence lifetime and fluorescence quantum yield. These properties allowed HARCP as a powerful photoreductant to efficiently realize a series of benchmark reactions, including photoreduction, alkoxylation and hydroxylation to construct C–H and C–O bonds using aryl halides as substrates under mild conditions, all of which have never been achieved by the same photocatalyst. Thus, this study well supports the notion that the principle between structural manipulation and photocatalytic activity is of great significance to design customized photocatalysts for photoredox chemistry.
- Guo, Baodang,Huang, Shuping,Li, Jia,Li, Min,Liu, Xuanzhong,Rao, Yijian,Wu, Yawen,Yin, Huimin,Yuan, Zhenbo,Zhang, Yan
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p. 111 - 120
(2021/06/16)
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- Energy-Transfer-Mediated Photocatalysis by a Bioinspired Organic Perylenephotosensitizer HiBRCP
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Energy transfer plays a special role in photocatalysis by utilizing the potential energy of the excited state through indirect excitation, in which a photosensitizer determines the thermodynamic feasibility of the reaction. Bioinspired by the energy-transfer ability of natural product cercosporin, here we developed a green and highly efficient organic photosensitizer HiBRCP (hexaisobutyryl reduced cercosporin) through structural modification of cercosporin. After structural manipulation, its triplet energy was greatly improved, and then, it could markedly promote the efficient geometrical isomerization of alkenes from the E-isomer to the Z-isomer. Moreover, it was also effective for energy-transfer-mediated organometallic catalysis, which allowed realization of the cross-coupling of aryl bromides and carboxylic acids through efficient energy transfer from HiBRCP to nickel complexes. Thus, the study on the relationship between structural manipulation and their photophysical properties provided guidance for further modification of cercosporin, which could be applied to more meaningful and challenging energy-transfer reactions.
- Zhang, Yan,Xia, Mingze,Li, Min,Ping, Qian,Yuan, Zhenbo,Liu, Xuanzhong,Yin, Huimin,Huang, Shuping,Rao, Yijian
-
p. 15284 - 15297
(2021/11/01)
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- Visible light-mediated transition metal-free esterification of amides with boronic acids
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A novel strategy for visible light-mediated esterification of amides with boronic acids in air has been described. This method is characterized by mild reaction conditions and low cost owing to no need of any catalyst, which implies high potential utility in late-stage functionalization of amide drugs and materials.
- Ding, Hao,Qi, Wan-Ying,Zhen, Jing-Song,Ding, Qiuping,Luo, Yong
-
supporting information
(2020/10/02)
-
- Dual aminoquinolate diarylboron and nickel catalysed metallaphotoredox platform for carbon-oxygen bond construction
-
Herein, aminoquinolate diarylboron complexes are utilized as photocatalysts in dual Ni/photoredox catalyzed carbon-oxygen construction reactions. Via this unified metallaphotoredox platform, diverse (hetero)aryl halides can be conveniently coupled with acids, alcohols and water. This method features operational simplicity, broad substrate scope and good compatibility with functional groups. This journal is
- Day, Craig,Jia, Xin,Wei, Lanfeng,Xu, Liang,Zu, Weisai
-
supporting information
p. 8273 - 8276
(2020/08/17)
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- Hexaacyl reductive cercosporin photocatalyst, and preparation method and application thereof
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The invention discloses a hexacyloyl reductive cercosporin photocatalyst and preparation and application thereof, belonging to the technical field of preparation methods and organic synthesis of catalysts. The preparation method comprises the following steps: adding anhydride into a mixture of cercosporin, a reducing agent and alkali, carrying out stirring at room temperature for 1-3 hours, addinganhydride, continuing reacting for 1-3 hours, and carrying out suction filtration, extraction, concentration and column chromatography purification to obtain the catalyst. The catalyst provided by the invention can catalyze reduction, coupling and other photochemical reactions of halogenated hydrocarbons, and has strong reaction activity and industrialization prospects.
- -
-
Paragraph 0085-0087
(2020/11/12)
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- Tropolonate salts as acyl-transfer catalysts under thermal and photochemical conditions: Reaction scope and mechanistic insights
-
Acyl-transfer catalysis is a frequently used tool to promote the formation of carboxylic acid derivatives, which are important synthetic precursors and target compounds in organic synthesis. However, there have been only a few structural motifs known to efficiently catalyze the acyl-transfer reaction. Herein, we introduce a different acyl-transfer catalytic paradigm based on the tropolone framework. We show that tropolonate salts, due to their strong nucleophilicity and photochemical activity, can promote the coupling reaction between alcohols and carboxylic acid anhydrides or chlorides to give products under thermal or blue light photochemical conditions. Kinetic studies and density functional theory calculations suggest interesting mechanistic insights for reactions promoted by this acyl-transfer catalytic system.
- Mai, Binh Khanh,Koenigs, Rene M.,Nguyen, Thanh Vinh,Lyons, Demelza J.M.,Empel, Claire,Pace, Domenic P.,Dinh, An H.
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p. 12596 - 12606
(2020/11/18)
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- Selectivity in the photo-fries rearrangement of some aryl benzoates in green and sustainable media. Preparative and mechanistic studies
-
Irradiation of a series of p-substituted aryl benzoates under N2 atmosphere in homogeneous and micellar media was investigated by means of steady-state condition and of time-resolved spectroscopy. A notable selectivity in favor of the 2-hydroxybenzophenone derivatives was observed in micellar media. The benzophenone derivatives were the main photoproduct. On the other hand, in homogeneous media (cyclohexane, acetonitrile, and methanol) the observed product distribution was entirely different, viz. substituted 2-hydroxybenzophenones, p-substituted phenols, benzyl and benzoic acid were found. The binding constants in the surfactant were also measured and NOESY experiments showed that the aryl benzoates were located in the hydrophobic core of the micelle. Laser flash photolysis experiments led to the characterization of both p-substituted phenoxy radical and substituted 2-benzoylcyclohexadienone transients in homogeneous and micellar environment.
- Siano, Gastón,Bonesi, Sergio M.,Crespi, Stefano,Mella, Mariella
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p. 4338 - 4352
(2019/05/01)
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- Overcoming solid handling issues in continuous flow substitution reactions through ionic liquid formation
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Substitutions such as acylations, arylations, and alkylations are some of the most commonly run reactions for building complex molecules. However, the requirement of a stoichiometric base to scavange acid by-products creates significant challenges when operating in continuous flow due to solid handling issues associated with precipitating base·HX salts. We present a general and simple strategy to overcome these solid handling issues through the use of acid scavenging organic bases that generate low- to moderate-melting ionic liquids upon protonation. The application of these bases towards the most commonly run substitutions are demonstrated, enabling reactions to be run in flow without requiring additional equipment, specific solvents, or dilute reaction conditions to prevent clogging.
- Kashani, Saeed,Sullivan, Ryan J.,Andersen, Mads,Newman, Stephen G.
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supporting information
p. 1748 - 1753
(2018/04/30)
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- Transition-Metal-Free Poly(thiazolium) Iodide/1,8-Diazabicyclo[5.4.0]undec-7-ene/Phenazine-Catalyzed Esterification of Aldehydes with Alcohols
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Poly(3,4-dimethyl-5-vinylthiazolium) iodide was used as a polymer precatalyst in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and phenazine for the oxidative esterification of aldehydes with alcohols. Selective functionalization of OH groups was achieved in the presence of NH2 groups. The poly(thiazolium) iodide/DBU/phenazine system exhibited excellent catalytic activity and could be reused five times without loss of activity.
- Chun, Supill,Chung, Young Keun
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supporting information
p. 3787 - 3790
(2017/07/26)
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- Diacyl Disulfide: A Reagent for Chemoselective Acylation of Phenols Enabled by 4-(N,N-Dimethylamino)pyridine Catalysis
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A general and excellent acylation reagent, diacyl disulfide, was uncovered for efficient ester formation enabled by DMAP (4-(N,N-dimethylamino)pyridine) catalysis. This protocol offered a promising synthetic platform on site-selective acylation of phenolic and primary aliphatic hydroxyl groups, which greatly expanded the realm of protecting group chemistry. The importance of the reagent was also reflected by its excellent moisture tolerance, high efficiency, and potential in synthetic chemistry and biologically meaningful natural product modification.
- Liu, Hong-Xin,Dang, Ya-Qian,Yuan, Yun-Fei,Xu, Zhi-Fang,Qiu, Sheng-Xiang,Tan, Hai-Bo
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supporting information
p. 5584 - 5587
(2016/11/17)
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- Reactions of aryl benzoates with potassium aryloxides: Solvent effects on reaction pathway and kinetics
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Temperature dependences of the relative reactivity of potassium aryloxides XC6H4O-K+ toward 2,4-dinitrophenyl benzoate in 50 mol% dimethylformamide (DMF)-50 mol% H2O mixture have been studied using the competitive reactions technique. Correlation analyses of the relative rate constants kX/kH and differences in the activation parameters (ΔΔCyrillic capital letter en≠ and ΔΔS≠) of the competitive reactions have revealed the existence of two isokinetic series of the reactions of 2,4-dinitrophenyl benzoate with potassium aryloxides with electron-donating substituent (EDS) and electron-withdrawing substituent (EWS), respectively. We have investigated the effect of the substituent X on the activation parameters for each isokinetic series and concluded that the mechanism of the reactions of 2,4-dinitrophenyl benzoate with potassium aryloxides XC6H4O-K+ in 50 mol% DMF-50 mol% H2O mixture is the same as in DMF. Analysis of the obtained data with using the method of two-dimensional reaction coordinate diagram leads to the conclusion that the variation of the solvent from DMF to 50 mol% DMF-50 mol% H2O mixture affects the reaction pathway. The rate constant kX for the reaction of 3-nitrophenyl benzoate with potassium 4-methoxyphenoxide and the relative rate constants kX/kH for the reaction of 3-nitrophenyl benzoate with potassium aryloxides XC6H4O-K+ with EDS were measured in 50 mol% DMF-50 mol% H2O mixtures at 25C, and it has been shown that the addition of water to DMF does not change the mechanism but slows down these reactions.
- Khalfina, Irina A.
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p. 302 - 314
(2015/04/14)
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- Nucleophilic substitution reactions of Y-Substituted-Phenyl Benzoates with Potassium Ethoxide in Anhydrous Ethanol: Reaction Mechanism and Role of K+ Ion
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Pseudo-first-order rate constants (kobsd) have been measured spectrophotometrically for the reactions of Ysubstituted-phenyl benzoates (5a-j) with potassium ethoxide (EtOK) in anhydrous ethanol at 25.0 ± 0.1 °C. The plots of kobsd vs. [EtOK] curve upward regardless of the electronic nature of the substituent Y in the leaving group. Dissection of kobsd into the second-order rate constants for the reactions with the dissociated EtOV and ion-paired EtOK (i.e., kEtO-and kEtOK, respectively) has revealed that the ion-paired EtOK is more reactive than the dissociated Et-V. The Bronsted-type plots for the reactions with the dissociated Et-V and ion-paired EtOK exhibit highly scattered points with βlg = -0.5 ± 0.1. The Hammett plots correlated with ao constants result in excellent linear correlations, indicating that no negative charge develops on the O atom of the leaving Ysubstituted-phenoxide ion in transition state. Thus, it has been concluded that the reactions with the dissociated EtOV and ion-paired EtOK proceed through a stepwise mechanism, in which departure of the leaving group occurs after the RDS, and that K+ ion catalyzes the reactions by increasing the electrophilicity of the reaction center through a four-membered cyclic TS structure.
- Kim, Song-I,Cho, Hyo-Jin,Um, Ik-Hwan
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p. 177 - 181
(2014/02/14)
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- Enthalpy-entropy correlations in reactions of aryl benzoates with potassium aryloxides in dimethylformamide
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Temperature dependences of the relative reactivity of potassium aryloxides XC6H4O-K+ toward 4-nitrophenyl (1), 3-nitrophenyl (2), 4-chlorophenyl (3), and phenyl (4) benzoates in dimethylformamide (DMF) were studied using the competitive reactions technique. The rate constants kX for the reactions of 1 with potassium 4-cyanophenoxide, 2 with potassium 3-bromophenoxide, 3 with potassium 3-bromo-, 4-bromo-, and unsubstituted phenoxides, 4 with potassium 4-methoxy- and 3-methylphenoxides were measured at 25°C. Correlation analysis of the relative rate constants kX/kH(3-Me) and differences in the activation parameters (δδH≠and δ δS ≠) of competitive reactions revealed the existence of six isokinetic series. We investigated the substituent effect of X on the activation parameters for each isokinetic series and concluded that the reactions of aryl benzoates PhCO2C6H4Y with potassium aryloxides in DMF proceed via a four-step mechanism. The large ρ0(Y) and ρXY values at 25°C obtained for the reactions of 1-3 with potassium aryloxides with an electron-donating substituent refer to the rate-determining formation of the spiro-σ-complex. The Hammett plots for the reactions of 1 and 2 exhibit a downward curvature, causing the motion of the transition state for the rate-determining step according to a Hammond effect as the substituent in aryloxide changes from electron-donating to electron-withdrawing. Analysis of data in the terms of two-dimensional reaction coordinate diagrams leads to the conclusion that significant anti-Hammond effects arise in the cases of ortho-substituted and unsubstituted substrates. It was shown that the isokinetic and compensation effects observed for the reactions of aryl benzoates with potassium aryloxides in DMF can be interpreted in the terms of the electrostatic bonding between the reaction centers.
- Khalfina, Irina A.,Vlasov, Vladislav M.
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p. 266 - 282
(2013/05/21)
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- Palladium-catalyzed aerobic oxidative coupling of acyl chlorides with arylboronic acids
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The first example of a palladium-catalyzed aerobic oxidative coupling of acyl chlorides with arylboronic acids has been developed, leading to a wide range of aryl benzoates in good to excellent yields. This catalytic system shows broad functional group tolerance. Preliminary mechanistic experiments using deuterium labeling showed that the oxygen atom was derived from dioxygen. Copyright
- Chen, Jiuxi,Peng, Yong,Liu, Miaochang,Ding, Jinchang,Su, Weike,Wu, Huayue
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supporting information
p. 2117 - 2122
(2012/11/07)
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- Rhodium-catalyzed cleavage reaction of aryl methyl ethers with thioesters
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A rhodium complex catalyzed the reaction of aryl methyl ethers and thioesters giving the corresponding aryl esters and methyl sulfides. S-(p-Chlorophenyl) p-(dimethylamino)benzothioate was used for the reaction of methyl aryl ethers with electron-withdrawing groups, and an S-(p-tolyl) derivative was used for those with electron-donating groups. Polymethoxybenzenes were converted to the esters in a regioselective manner.
- Arisawa, Mieko,Nihei, Yuri,Suzuki, Takaaki,Yamaguchi, Masahiko
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body text
p. 855 - 857
(2012/03/26)
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- Ruthenium/NHC-catalyzed tandem benzylic oxidation/oxidative esterification of benzylic alcohols with phenols
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An efficient methodology to access benzoate derivatives via tandem benzylic oxidation/oxidative esterification of benzylic alcohols with phenols catalyzed by ruthenium/NHC was developed. This operationally simple one-pot process uses O2 as the clean oxidant, producing esters in good to excellent yields.
- Zhang, Di,Pan, Changduo
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experimental part
p. 41 - 45
(2012/06/18)
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- Enthalpy-entropy correlations in reactions of 2,4-dinitrophenyl benzoate with phenols in the presence of potassium hydrogen carbonate and with potassium phenoxides in dimethylformamide
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Temperature dependences of the relative reactivity of substituted phenols RC6H4OH in the presence of potassium hydrogen carbonate and of potassium phenoxides RC6H4O-K + toward 2,4-dinitrophenyl benzoate in dimethylformamide were studied using the competitive reactions technique. Correlation analysis of the relative rate constants kR/kH and differences in the activation parameters (ΔΔH{double barred pipe} and ΔΔS{double barred pipe}) of competitive reactions revealed the existence of two isokinetic series for each type of nucleophiles. The mechanism of transesterification was interpreted in terms of an approach based on analysis of the effect of substituent in the nucleophile on the activation parameters. Pleiades Publishing, Ltd., 2011.
- Khalfina,Vlasov
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experimental part
p. 845 - 854
(2011/10/19)
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- Equilibrium shift in the rhodium-catalyzed acyl transfer reactions
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Rhodium/phosphine complexes catalyze equilibrium acyl transfer reactions between acid fluorides, aryl esters, acylphosphine sulfides, and thioesters. The use of appropriate co-substrates to accept heteroatom groups shifted the equilibrium to desired products. Acylphosphine sulfides and aryl esters were converted to acid fluorides using benzoylpentafluorobenzene as the fluoride donor, and the fluorination reaction of thioesters employed (4-tolylthio) pentafluorobenzene. Acid fluorides were converted into acylphosphine sulfides and thioesters using diphosphine disulfides and disulfides/triphenylphosphine, respectively. Aryl esters were obtained from acid fluorides and phenols in the presence of triphenylsilane. Aryl esters, acylphosphine sulfides, and thioesters were also interconverted in the presence of rhodium complexes. These rhodium-catalyzed acyl transfer reactions proceeded under neutral conditions without using acid or base. The involvement of acyl rhodium intermediates in these reactions was suggested by the carbothiolation reaction of thioesters and alkynes.
- Arisawa, Mieko,Igarashi, Yui,Kobayashi, Haruki,Yamada, Toru,Bando, Kentaro,Ichikawa, Takuya,Yamaguchi, Masahiko
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p. 7846 - 7859
(2011/10/12)
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- Palladium/NHC-catalyzed tandem benzylic oxidation/oxidative esterification of benzylic alcohols with phenols
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A palladium/NHC-catalyzed tandem benzylic oxidation/oxidative esterification of benzylic alcohols with phenols to access aryl benzoate derivatives is described. The procedure tolerates a series of functional groups, such as methoxy, nitro, cyano, chloro, fluoro and bromo groups. Thus, it represents a practically alternative method to access aryl benzoate derivatives.
- Luo, Fang,Pan, Changduo,Cheng, Jiang,Chen, Fan
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supporting information; experimental part
p. 5878 - 5882
(2011/09/12)
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- Palladium/NHC-catalyzed oxidative esterification of aldehydes with phenols
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A palladium-catalyzed oxidative esterification of aldehydes with phenols is described, using air as the clean oxidant. This reaction tolerates many functional groups, providing esters with yields ranging from moderate to excellent.
- Zhang, Manli,Zhang, Shouhui,Zhang, Guoying,Chen, Fan,Cheng, Jiang
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experimental part
p. 2480 - 2483
(2011/05/16)
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- NHC/Iron cooperative catalysis: Aerobic oxidative esterification of aldehydes with phenols
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An NHC/iron cooperative catalytic system mediates the aerobic oxidative esterification of aldehydes with phenols. The use of equimolar amounts of reactants led to good to excellent isolated yields of esters.
- Reddy, R. Sudarshan,Rosa, Joao N.,Veiros, Luis F.,Caddick, Stephen,Gois, Pedro M. P.
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supporting information; experimental part
p. 3126 - 3129
(2011/05/12)
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- Kinetics and mechanism of nucleophilic displacement reactions of Y-substituted phenyl benzoates with cyanide Ion
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Second-order rate constants (kCN-) have been measured for nucleophilic substitution reactions of Y-substituted phenyl benzoates (1a-r) with CN- ion in 80 mol % H2O/20 mol % DMSO at 25.0 ± 0.1 °C. The Bronsted-type plot is linear with βlg = -0.49, a typical βlg value for reactions reported to proceed through a concerted mechanism. Hammett plots correlated with σo and σ-constants exhibit many scattered points. In contrast, the Yukawa-Tsuno plot for the same reaction exhibits excellent linearity with pY = 1.37 and r = 0.34, indicating that a negative charge develops partially on the oxygen atom of the leaving aryloxide in the rate-determining step (RDS). Although two different mechanisms are plausible (i.e., a concerted mechanism and a stepwise pathway in which expulsion of the leaving group occurs at the RDS), the reaction has been concluded to proceed through a concerted mechanism on the basis of the magnitude of βlg and pY values.
- Kim, Song-I,Kim, Eun-Hee,Um, Ik-Hwan
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experimental part
p. 689 - 693
(2010/08/19)
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- Aminolysis of 2,4-dinitrophenyl X-substituted benzoates and Y-substituted phenyl benzoates in MeCN: Effect of the reaction medium on rate and mechanism
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Second-order rate constants (kN) have been determined spectrophotometrically for the reactions of 2,4-di-nitrophenyl X-substituted benzoates (1a-f) and Y-substituted phenyl benzoates (2a-h) with a series of alicyclic secondary amines in MeCN at
- Um, Ik-Hwan,Jeon, Sang-Eun,Seok, Jin-Ah
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p. 1237 - 1243
(2008/09/18)
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- A simple and efficient transprotection of aryl methyl ether to aryl benzoate under microwave activation
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A simple and efficient method for the transprotection of aryl methyl ether to easily cleavable arylbenzoate mediated by microwave activation has been developed. One important feature of this method is its high tolerance towards sensitive functionalities and to some extent to bulky environment.
- Marette, Caroline,Larrouquet, Camille,Tisnès, Pierre,Deloye, Jean-Bernard,Gras, Emmanuel
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p. 6947 - 6950
(2007/10/03)
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- Kinetic study of hydrolysis of benzoates. Part XXIV-variation of the ortho substituent effect with solvent in the alkaline hydrolysis of substituted phenyl benzoates
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The second-order rate constants k2 (M-1 s -1 ) for the alkaline hydrolysis of meta-, para- and orthosubstituted phenyl benzoates, C6H5CO 2C6H4X, in aqueous 0.5 M n-Bu4NBr were measured spectrophotometrically. The dependence of substituent effects, especially ortho inductive, resonance and steric terms on different solvent parameters, was studied using the following equation: Δ log k ortho = c0 + c1(ortho) σ1 + c2(ortho) σR0 + c 3(ortho)EsB + c4ΔE + c 5ΔY + c6ΔP + c7(ortho) ΔEσI + c8(ortho)ΔYσI + c9(ortho) ΔPσI + c10(ortho) ΔEσR0 + c11(ortho) ΔYσR0 + c12(ortho) ΔPσR0 where Δlog k = log kX - log KH, σI, σR0 and E SB are the inductive, resonance and steric substituent constants and E, Y and P are the solvent electrophilicity, polarity and polarizability parameters, respectively. In data treatment ΔE = E s - EH2O, ΔY = YS -YH2O and ΔP = PS - PH2O were used. The solvent electrophilicity was found to be the main factor responsible for changes in the ortho, para and meta polar substituent effects with medium. The variation of the ortho inductive term with the solvent electrophilicity ES was found to be ca threefold smaller than that for para substituents, whereas the ortho resonance term appeared to vary with solvent very similarly to that for para substituents. The steric term of ortho substituents was found to be approximately independent of solvent parameters. The ortho effect caused by the supplementary inductive effect from ortho position was found to disappear in a solvent whose electrophilic solvating power is comparable to that of 60% aqueous ethanol (E ≈ 13.3). Copyright
- Nummert, Vilve,Piirsalu, Mare,Maeemets, Vahur,Koppel, Ilmar
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p. 1138 - 1144
(2007/10/03)
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- Evidence of substituent-induced electronic interplay. Effect of the remote aromatic ring substituent of phenyl benzoates on the sensitivity of the carbonyl unit to electronic effects of phenyl or benzoyl ring substituents
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Carbonyl carbon 13C NMR chemical shifts δC(C=O) measured in this work for a wide set of substituted phenyl benzoates p-Y-C 6H4CO2C6H4-p-X (X = NO2, CN, Cl, Br, H, Me, or MeO; Y = NO2, Cl, H, Me, MeO, or NMe2) have been used as a tool to study substituent effects on the carbonyl unit. The goal of the work was to study the cross-interaction between X and Y in that respect. Both the phenyl substituents X and the benzoyl substituents Y have a reverse effect on δC(C=O). Electron-withdrawing substituents cause shielding while electron-donating ones have an opposite influence, with both inductive and resonance effects being significant. The presence of cross-interaction between X and Y could be clearly verified. Electronic effects of the remote aromatic ring substituents systematically modify the sensitivity of the C=O group to the electronic effects of the phenyl or benzoyl ring substituents. Electron-withdrawing substituents in one ring decrease the sensitivity of δC(C=O) to the substitution of another ring, while electron-donating substituents inversely affect the sensitivity. It is suggested that the results can be explained by substituent-sensitive balance of the contributions of different resonance structures (electron delocalization, Scheme 1).
- Neuvonen, Helmi,Neuvonen, Kari,Pasanen, Paavo
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p. 3794 - 3800
(2007/10/03)
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- Electrostatic catalysis by ionic aggregates: Scope and limitations of Mg(ClO4)2 as acylation catalyst
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Alkali and alkaline earth metal perchlorates exhibit electrostatic catalysis in the activation of anhydrides for the acylation reaction. Perchlorates with higher values of the charge-size function of the metal ion exhibit better catalytic activity following the order Mg(ClO4) 2>Ba(ClO4)2>LiClO4. Acylation of structurally diverse phenols, thiols, alcohols, and amines have been carried out with stoichiometric amounts of anhydride at room temperature under solvent free conditions in the presence of catalytic amount of Mg(ClO4) 2. Sterically hindered and electron deficient phenols are efficiently acylated. Acylation with sterically hindered anhydrides such as iso-butyric, pivalic, and benzoic anhydrides are carried out with phenols and alcohols in excellent yields. Acid-sensitive alcohols are acylated in excellent yields without any competitive side reactions.
- Chakraborti, Asit K.,Sharma, Lalima,Gulhane, Rajesh,Shivani
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p. 7661 - 7668
(2007/10/03)
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- Photochemical generation of the N-isopropylbenzonitrilium ion and unusually slow trapping by azide ion
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The imidate ester 4-cyanophenyl N-isopropylbenzimidate undergoes efficient photoheterolysis in water producing the 4-cyanophenoxide ion and the N-isopropylbenzonitrilium ion. The latter is detected as a transient intermediate in flash photolysis experiments and has a relatively long lifetime (1/kw) in water of 2.5 ms. The rate constants for hydroxide and azide are respectively 5.2 × 106 and 3.9 × 106 dm3 mol-1 s-1. This pattern is not seen with sp2 hybridized cations, where kaz is normally significantly greater than kOH. Further indications that azide ion is unexpectedly poor as a trap for this cation is seen in considering the kaz:kw value in the context of ratios directly measured for sp2 hybridized cations. For the latter a kaz:kw of less than 105 can be taken to mean that the reaction with azide is at (or certainly very close to) the diffusion limit (i.e. 5-10 × 109 dm3 mol-1 s-1). The nitrilium ion 3 has kaz:kw equal to only 104 mol-1 dm3 and yet its azide reaction is three orders of magnitude slower than diffusion.
- Ruane, Patrick H.,McClelland, Robert A.,Hegarty, A. Frank,Steenken, Steen
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- Ruthenium-Catalyzed Oxidations of Alcohols
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A combination of low-valent ruthenium complexes and peroxides such as t-BuOOH and peracids serves as efficient catalytic systems for the oxidation of aromatic and aliphatic hydroxy compounds. The utility of these methods was demonstrated by the synthesis of acyl cyanides which are versatile synthetic intermediates. The principle of the catalytic oxidations with peracids lead to the novel and efficient method for aerobic oxidation of alcohols in the presence of aldehydes. This reaction is of importance in synthetic and large scale industrial processes and from environmental points of view. The present principle will provide new chemistry of oxidative transformations of various industrially important functional materials.
- Murahashi,Naota
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p. 203 - 213
(2007/10/03)
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- Palladium-Catalyzed Decarbonylation of Acyl Cyanides
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The palladium-catalyzed decarbonylation of aromatic and heteroaromatic acyl cyanides 1 gives the corresponding nitriles 2 in excellent yields.Alkylacyl cyanides can be converted into the corresponding alkenes via decarbonylation followed by β-elimination of hydrogen cyanide.Because of easy preparation of acyl cyanides by the oxidation of cyanohydrins, the present decarbonylation reaction provides an efficient method for the preparation of nitriles from aldehydes under mild and neutral conditions.The catalytic decarbonylation involves the following processes; oxidative addition of acyl cyanides 1 to Pd(PPh3)4 to give acylpalladium complexes 13, acyl-aryl rearrangement, reductive elimination.When an acyl cyanide has a β-hydrogen, the intermediate cyanoalkylcarbonylpalladium (15) undergoes β-elimination to give alkenes.
- Murahashi, Shun-Ichi,Naota, Takeshi,Nakajima, Nobuyuki
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p. 898 - 901
(2007/10/02)
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- Liquid crystal mixture
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There is described a liquid crystalline mixture for electro-optical devices which are operated according to the two-frequency matrix addressing procedure. The mixture consists of three components A, B and C, each of which contains one or more compounds. Component A has a viscosity of at most about 40 cp, a clearing point of at least about 40° C. and a dielectric anisotropy between about -2 and about +1. Component B has a dielectric anisotropy below about -2 and component C has a dielectric anisotropy above about +10, a clearing point of at least about 100° C. and there is a cross-over frequency in the total mixture of at most about 15 kHz at 20° C. Novel compounds for such mixtures and their manufacture and use are also described. The novel mixtures make possible especially high multiplex rates and short response times.
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