- A study of electronic effects on the kinetics of thermal deamination of N-nitrosoamides
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N-4-R-Benzyl-N-nitrosopivalamides (1a-d; R = MeO, Me, H, NO2) were allowed to decompose at 18 °C in C6D12, CDCl3, CD3CN, and d6-DMSO, and the rates of decomposition were followed by 1H NMR spectroscopy. The half-lives of the nitrosoamides were found to vary in a systematic way with the nature of the R group on the aromatic nucleus. Electron-releasing groups were found to decrease the stability of the starting nitrosoamide, whereas electron-withdrawing ones increased the nitrosoamides' thermal stability. A Hammett-type plot of log(rate constants of deamination) vs σp was linear (R2 = 0.986) with a ρ-type value of -0.90 indicating development of significant positive charge at the benzylic position in the transition state of the rate-determining step. The thermal stability of the nitrosoamides was also found to be systematically affected by the polarity of the solvent: as the solvent polarity increased, so did the lability of the nitrosoamides. This observation of intra- and intermolecular electronic perturbations of the kinetics of nitrosoamide decomposition appears to be novel. A closer look at the rate-determining step of nitrosoamide thermolysis is made, and a mechanistic framework is proposed that accounts for both steric and electronic modulation of nitrosoamide stability as well as the greater thermal stabilities of the related N-nitrocarboxamides and N-nitrosotosylamides.
- Darbeau,Pease,Gibble
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Read Online
- Nickel-catalyzed direct C-H/C-O cross couplings generating fluorobenzenes and heteroarenes
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The Ni-catalyzed direct C-H/C-O cross couplings of benzylic alcohol derivatives with fluorobenzenes and heteroarenes are disclosed. This transformation provides a straightforward and efficient method for the synthesis of these valuable heteroatom-containing compounds.
- Xiao, Jing,Chen, Tieqiao,Han, Li-Biao
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Read Online
- A solvent-reagent selection guide for Steglich-type esterification of carboxylic acids
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The Steglich esterification is a widely employed method for the formation of esters under mild conditions. A number of issues regarding the sustainability of this transformation have been identified, chiefly the use of hazardous carbodiimide coupling reagents in conjunction with solvents with considerable issues such as dichloromethane (DCM) and N,N-dimethylformamide (DMF). To overcome these issues, we have developed a solvent-reagent selection guide for the formation of esters via Steglich-type reactions with the aim of providing safer, more sustainable conditions. Optimum reaction conditions have been identified after high-throughput screening of solvent-reagent combinations, namely the use of Mukaiyama's reagent (Muk) in conjunction with solvent dimethyl carbonate (DMC). The new reaction conditions were also exemplified through the synthesis of a small selection of building-block like molecules and includes the formation of t-butyl esters.
- Jordan, Andrew,Sneddon, Helen F.,Sydenham, Jack,Whymark, Kyran D.
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supporting information
p. 6405 - 6413
(2021/09/10)
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- Epoxide as precatalyst for metal-free catalytic transesterification
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Transesterification of methyl esters was accelerated by an in situ-generated metal-free catalyst comprising a quaternary alkylammonium salt and an epoxide. The combination of a quaternary alkylammonium acetate and glycidol is optimal, and various esters were synthesized from methyl esters with alcohols in good to excellent yield. Analysis of the catalyst solution revealed that basic species are generated by the ring-opening reaction of epoxide.
- Tanaka, Shinji,Nakashima, Takuya,Satou,Oono, Hiromi,Kon, Yoshihiro,Tamura, Masanori,Sato, Kazuhiko
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p. 2009 - 2013
(2019/07/03)
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- Visible light-induced transformation of aldehydes to esters, carboxylic anhydrides and amides
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A transition metal- and organophotocatalyst free synthesis of esters, carboxylic anhydrides and amides from aldehydes induced by visible-light has been reported. The proposed methodology can be carried out by the use of sunlight or artificial visible light as a blue LED source. The methodology has a very broad applicability and the desired products are obtained in very satisfactory yields.
- Gaspa, Silvia,Raposo, Inês,Pereira, Leonor,Mulas, Gabriele,Ricci, Pier Carlo,Porcheddu, Andrea,De Luca, Lidia
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supporting information
p. 10711 - 10715
(2019/07/15)
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- Nickel-Catalyzed Benzylic Substitution of Benzyl Esters with Malonates as a Soft Carbon Nucleophile
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The nickel-catalyzed benzylic substitution of benzyl alcohol derivatives with a soft carbon nucleophile is extremely rare compared to that with a hard carbon nucleophile. We have achieved the nickel-catalyzed benzylic substitution of benzyl esters with malonates as a soft carbon nucleophile. Primary and secondary benzyl 2,3,4,5,6-pentafluorobenzoates as well as a wide variety of malonate derivatives were well tolerated in the nickel-catalyzed reaction, providing the corresponding alkylation products in 46-86% yields (34 examples). Additionally, we propose a possible reaction mechanism that would undergo via the ??1- A nd ??3-benzylnickel intermediates.
- Tsuji, Hiroaki,Hashimoto, Keisuke,Kawatsura, Motoi
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supporting information
p. 8837 - 8841
(2019/11/11)
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- Sterically congested ester formation from α-substituted malononitrile and alcohol by an oxidative method using molecular oxygen
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A metal-free oxidative esterification or thio-esterifica-tion of readily available substituted malononitrile and alcohol or thiol has been developed by simply mixing α-substituted malononitrile and alcohol or thiol in the presence of base under a molecular oxygen atmosphere. Sterically hindered ester or thioester can be prepared efficiently.
- Hayashi, Yujiro,Li, Jing,Asano, Hirotaka,Sakamoto, Daisuke
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supporting information
p. 675 - 677
(2018/11/23)
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- Reusable and efficient polyvinylpolypyrrolidone-supported triflic acid catalyst for acylation of alcohols, phenols, amines, and thiols under solvent-free conditions
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Abstract: A triflic acid-functionalized polyvinylpolypyrrolidone was prepared and fully characterized by FT-IR, TGA, and SEM. This super acidic solid catalyst shows high catalytic activity for selective acylation of alcohols, phenols, amines, and thiols with anhydrides under solvent-free conditions at room temperature. In addition, this method features an easy to handle solid super acid catalyst and an operationally simple procedure, affording the desired acylated products in excellent yields. Graphical abstract: [Figure not available: see fulltext.].
- Tajbakhsh, Mahgol,Tajbakhsh, Mahmoud,Khaksar, Samad,Gazvini, Helia Janatian,Heidary, Marzieh
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p. 1117 - 1122
(2017/05/10)
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- Iodobenzene Dichloride in the Esterification and Amidation of Carboxylic Acids: In-Situ Synthesis of Ph3PCl2
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A novel, in-situ synthesis of dichlorotriphenylphosphorane (Ph3PCl2) is accomplished upon combining PPh3and the easily prepared hypervalent iodine reagent iodobenzene dichloride (PhICl2). The phosphorane is selectively generated in the presence of carboxylic acid or alcohol residues to rapidly produce acyl chlorides and alkyl chlorides in high yields. Addition of EtOH, PhOH, BnOH, Et2NH or CH2N2results in the direct synthesis of esters, amides and diazo ketones from carboxylic acids.
- Carle, Myriam S.,Shimokura, Grace K.,Murphy, Graham K.
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supporting information
p. 3930 - 3933
(2016/08/24)
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- METHOD OF CONVERTING ALCOHOL TO HALIDE
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The present invention relates to a method of converting an alcohol into a corresponding halide. This method comprises reacting the alcohol with an optionally substituted aromatic carboxylic acid halide in presence of an N-substituted formamide to replace a hydroxyl group of the alcohol by a halogen atom. The present invention also relates to a method of converting an alcohol into a corresponding substitution product. The second method comprises: (a) performing the method of the invention of converting an alcohol into the corresponding halide; and (b) reacting the corresponding halide with a nucleophile to convert the halide into the nucleophilic substitution product.
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Page/Page column 186; 187
(2017/01/02)
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- Metal-Free Direct Oxidation of Aldehydes to Esters Using TCCA
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Aromatic and aliphatic aldehydes are simply converted into esters by an efficient oxidative esterification carried out under mild conditions. The aldehydes are converted in situ into their corresponding acyl chlorides, which are then reacted with primary and secondary aliphatic, benzylic, allylic, and propargylic alcohols and phenols. A variety of esters are obtained in high yields.
- Gaspa, Silvia,Porcheddu, Andrea,De Luca, Lidia
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supporting information
p. 3666 - 3669
(2015/08/18)
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- Scandium triflate catalyzed ester synthesis using primary amides
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A scandium triflate (ScOTf)3 catalyzed methodology has been developed to synthesize esters from primary amides. Various primary and secondary aliphatic alcohols have been shown to react in n-heptane with a range of primary amides for 24 h.
- Atkinson, Benjamin N.,Williams, Jonathan M.J.
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supporting information
p. 6935 - 6938
(2015/01/16)
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- Convenient esterification of carboxylic acids by SN2 reaction promoted by a protic ionic-liquid system formed in situ in solvent-free conditions
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The reaction of esterification of benzoic acid with benzyl chloride was chosen as a model reaction to study the esterification by SN2 promoted by tertiary amine as deprotonating agent. The use of ionic liquid (IL) 1,3-dimethylimidazolium methanesulfonate [MMIm][OMs] as reaction medium has proven to give quantitative yield of the ester, but interestingly the reaction does occur even in solvent-free conditions, where the acid + the amine form a liquid system (a protic IL) in situ. This last methodology was extended to several carboxylic acids in conditions of atom economy (i.e., without excess of any reagent), giving moderately good yields of esters (54-78%) recovered by weight in pure form.
- Cardellini, Fabio,Brinchi, Lucia,Germani, Raimondo,Tiecco, Matteo
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p. 3248 - 3256
(2015/10/06)
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- ZnAl2O4@SiO2 nanocomposite catalyst for the acetylation of alcohols, phenols and amines with acetic anhydride under solvent-free conditions
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A ZnAl2O4@SiO2 nanocomposite was prepared from metal nitrates and tetraethyl orthosilicate by the sol-gel process, and characterized by X-ray diffraction, Fourier transform infrared, transmission electron microscopy, and N2 adsorption-desorption measurements. The nanocomposite was tested as a heterogeneous catalyst for the acetylation of alcohols, phenols, and amines under solvent-free conditions. Under optimized conditions, efficient acetylation of these substrates with acetic anhydride over the ZnAl2O4@SiO2 nanocomposite was obtained. Acetylation of anilines and primary aliphatic amines proceeded rapidly at room temperature, while the reaction time was longer for the acetylation of alcohols and phenols, showing that an amine NH2 group can be selectively acetylated in the presence of alcoholic or phenolic OH groups. The catalyst can be reused without obvious loss of catalytic activity. The catalytic activity of the ZnAl2O4@SiO2 nanocomposite was higher than that of pure ZnAl2O4. The method gives high yields, and is clean, cost effective, compatible with substrates having other functional groups and it is suitable for practical organic synthesis.
- Farhadi, Saeed,Jahanara, Kosar
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p. 368 - 375
(2014/04/03)
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- Nickel-catalyzed selective conversion of two different aldehydes to cross-coupled esters
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In the presence of a Ni(0)/NHC catalyst, an equimolar mixture of aliphatic and aryl aldehydes can be employed to selectively yield a single cross-coupled ester. This reaction can be applied to a variety of aliphatic (1°, 2°, cyc-2°, and 3°) and aryl aldehyde combinations. The reaction represents 100% atom efficiency and generates no waste. Mechanistic studies have revealed that the striking feature of the reaction is the simultaneous coordination of two aldehydes to Ni(0).
- Hoshimoto, Yoichi,Ohashi, Masato,Ogoshi, Sensuke
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supporting information; experimental part
p. 4668 - 4671
(2011/05/16)
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- H6GeMo10V2O40·16H 2O nanoparticles prepared by hydrothermal method: A new and reusable heteropoly acid catalyst for highly efficient acetylation of alcohols and phenols under solvent-free conditions
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A new Keggin-type heteropoly acid, namely decamolybdodivanadogermanic acid (H6GeMo10V2O40·16H 2O), with nanosized particles (5-8 nm), has been synthesized by a hydrothermal method and characterized by elemental analysis, thermogravimetric analysis (TGA), powder X-ray diffractometry (XRD), Fourier-transform infrared spectroscopy (FTIR), UV-Visible spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and potentiometric titration. H6GeMo10V2O40·16H 2O revealed high catalytic activity for acetylation of various alcohols and phenols with acetic anhydride at room temperature (298 ± 2 K) and under solvent-free conditions. The catalyst can be easily recovered and used repeatedly for five cycles with a slight loss of activity. The catalytic activity of H6GeMo10V2O40· 16H2O was higher than that of other Keggin-type heteropoly acids, such as H3PW12O40, H3PMo 12O40 and H4SiW12O40.
- Farhadi, Saeid,Zareisahamieh, Reza,Zaidi, Masoumeh
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experimental part
p. 1323 - 1332
(2012/04/04)
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- An efficient protocol for alcohol protection under solvent- and catalyst-free conditions
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(Chemical Equation Presented) Asimple and highly efficient protocol for pivaloylation of alcohols without using a catalyst under solvent-free conditions has been developed. The key advantages of the reaction are short reaction time, high yields, simple workup, and no need for further purification. Selectivity was observed between primary alcohols vs. secondary alcohols and aliphatic alcohols vs. aromatic alcohols. The accentuated and relevant phenomenon of this method that we observed is in one-pot conversion of TBS protection into Piv protection of the hydroxyl group. 2009 American Chemical Society.
- Rao, Ch. Bhujanga,Chinnababu,Venkateswarlu
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supporting information; experimental part
p. 8856 - 8858
(2010/02/17)
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- Cyclopropanecarboxylic acid esters as potential prodrugs with enhanced hydrolytic stability
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Esters of cyclopropanecarboxylic acid demonstrate a substantial increase in stability under both acid- and base-catalyzed hydrolytic conditions. Comparison of the stability of valacyclovir 13 with the cyclopropane analogue 14 shows that at 40 °C and pH 6 the half-life of 14 is >300 h while the value for 13 is 69.7 h. CBS-QB3 calculations on isodesmic reactions for transfer of groups from an alkane to an ester show that a cyclopropyl group provides hyperconjugative stabilization.
- Bender, David M.,Peterson, Jeffrey A.,McCarthy, James R.,Gunaydin, Hakan,Takano, Yu,Houk
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p. 509 - 511
(2008/09/19)
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- Synthesis of chloroesters by the cleavage of cyclic and acyclic ethers using La(NO3)3·6H2O as a mild and efficient catalyst under solvent-free conditions
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A mild and an efficient synthesis of chloroesters is described by the reaction of cyclic and acyclic ethers with acid chlorides in the presence of a catalytic amount of La(NO3)3·6H2O under solvent-free conditions, affording the corresponding chloroesters in excellent yields. Copyright Taylor & Francis Group, LLC.
- Suresh,Suryakiran,Rajesh,Selvam, J. Jon Paul,Srinivasulu,Venkateswarlu
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- A mild and efficient chemoselective protection of primary alcohols as pivaloyl esters using La(NO3)3·6H2O as a catalyst under solvent-free conditions
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Primary alcohols are selectively and efficiently protected as their pivaloyl esters with pivaloyl chloride in the presence of catalytic amounts of La(NO3)3·6H2O at room temperature under solvent-free conditions in excellent yields. Copyright
- Prabhakar,Suryakiran,Venkateswarlu
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p. 732 - 733
(2008/02/09)
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- A mild and efficient synthesis of chloroesters by the cleavage of cyclic and acyclic ethers using Bi(NO3)3·5H2O as a catalyst under solvent-free conditions
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A facile, efficient synthesis of chloroesters is described. The reaction of cyclic and acyclic ethers with acid chlorides in the presence of catalytic amounts of Bi(NO3)2·5H2O under solvent-free conditions yielded the corresponding chloroesters. Also, the catalyst can be recovered conveniently and reused efficiently for at least six times.
- Suresh,Suryakiran,Venkateswarlu
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p. 1037 - 1040
(2008/09/16)
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- Erbium(III) chloride: A very active acylation catalyst
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Erbium(iii) chloride is a powerful catalyst for the acylation of alcohols and phenols. The reaction works well for a large variety of simple and functionalized substrates by using different kinds of acidic anhydrides (Ac 2O, (EtCO)2O, (PriCO)2O, (Bu tCO)2O, and (CF3CO)2), without isomerization of chiral centres. Moreover, the catalyst can be easily recycled and reused without significant loss of activity. CSIRO 2007.
- Dalpozzo, Renato,De Nino, Antonio,Maiuolo, Loredana,Oliverio, Manuela,Procopio, Antonio,Russo, Beatrice,Tocci, Amedeo
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- Steric effects in the uncatalyzed and DMAP-catalyzed acylation of alcohols - Quantifying the window of opportunity in kinetic resolution experiments
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The kinetics of the reaction of several alcohols (benzyl alcohol, ethanol, 1-phenylethanol, cyclohexanol, and 1-methyl-1-phenylethanol) with a selection of anhydrides (acetic anyhydride, propionic anhydride, isobutyric anhydride, isovaleric anhydride, and pivalic anhydride) as catalyzed by 4-(N,N-dimethylamino)pyridine (DMAP)/triethyl amine have been studied in CH 2Cl2 at 20°C. In all cases the reaction kinetics can be described by rate laws containing a DMAP-catalyzed term and an uncatalyzed (back-ground) term. The rate constants for the background reaction respond sensi tively to changes in the steric demand of the alcohol and the anhydride substrates, making the reaction of cyclohexanol with acetic anhydride 526 times faster than the reaction with pivalic anhydride. Steric effects are even larger for the catalyzed reaction and the reactivity difference between acetic and pivalic anhydride exceeds a factor of 8000 for the reaction of cyclohexa nol. There is, however, no linear correlation between the steric effects on the catalyzed and the uncatalyzed part. As a consequence there are substrate combinations with dominating catalytic terms (such as the reaction of benzyl alcohol with isobutyric anhydride), while other substrate combinations (such as the reaction of cyclohexanol with pivalic anhydride) are characterized through a dominating background process. The implications of these findings for the kinetic resolution of alcohols are discussed.
- Fischer, Christian B.,Xu, Shangjie,Zipse, Hendrik
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p. 5779 - 5784
(2008/03/14)
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- Magnesium bistrifluoromethanesulfonimide as a new and efficient acylation catalyst
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Magnesium bistrifluoromethanesulfonimide catalyzed the acetylation of phenols, alcohols, and thiols under solvent-free conditions at room temperature and in short times. Electron-deficient and sterically hindered phenols provided excellent yields. The catalyst was found to be general for acylation with other anhydrides, such as propionic, isobutyric, pivalic, chloroacetic, and benzoic anhydrides. The rate of acylation was influenced by the electronic and steric factors associated with the anhydride. The reaction with less electrophilic anhydrides (e.g., chloroacetic and benzoic anhydrides) required higher temperature (~80 °C). Chemoselective acetylation, pivalation, and benzoylation took place with acid-sensitive alcohols without any competitive dehydration/rearrangement.
- Chakraborti, Asit K.,Shivani
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p. 5785 - 5788
(2007/10/03)
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- Enzymatic removal of carboxyl protecting groups. 2. Cleavage of the benzyl and methyl moieties
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Enzymes are versatile reagents for the efficient removal of methyl and benzyl protecting groups. An esterase from Bacillus subtilis (BS2) and a lipase from Candida antarctica (CAL-A) allow a mild and selective removal of these moieties in high yields without affecting other functional groups.
- Barbayianni, Efrosini,Fotakopoulou, Irene,Schmidt, Marlen,Constantinou-Kokotou, Violetta,Bornscheuer, Uwe T.,Kokotos, George
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p. 8730 - 8733
(2007/10/03)
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- Erbium(III) triflate as an extremely active acylation catalyst
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Erbium(III) triflate is a powerful catalyst for the acylation of alcohols and phenols. The reaction works well for a large variety of simple and functionalized substrates by using different kinds of acidic anhydrides {Ac 2O, (EtCO)2O, [(CH3)3CO] 2O, Bz2O, and (CF3CO)2O} without isomerisation of chiral centres. Moreover, the catalyst can be easily recycled and reused without significant loss of activity.
- Procopio, Antonio,Dalpozzo, Renato,De Nino, Antonio,Maiuolo, Loredana,Russo, Beatrice,Sindona, Giovanni
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p. 1465 - 1470
(2007/10/03)
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- Efficient method for the preparation of carboxylic acid alkyl esters or alkyl phenyl ethers by a new-type of oxidation-reduction condensation using 2,6-dimethyl-1,4-benzoquinone and alkoxydiphenylphosphines
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A new-type of oxidation-reduction condensation proceeded smoothly to afford carboxylic acid alkyl esters or alkyl phenyl ethers in good to high yields by combined use of alkoxydiphenylphosphines (1) having primary, bulky secondary or tertiary alkoxy groups, a mild quinone-type oxidant such as 2,6-dimethyl-1,4-benzoquinone (DMBQ) and carboxylic acids or phenols. Generally, alkoxydiphenylphosphines were prepared easily from chlorodiphenylphosphine (2) and alcohols in the presence of pyridine, and were isolated by distillation. On the other hand, the phosphines 1 were also prepared in situ from N,N-dimethylaminodiphenylphosphine (3a) and primary or secondary alcohols while primary, bulky secondary or tertiary alkoxydiphenylphosphines were alternatively formed in situ by adding 2 to the "BuLi-treated alcohols in order to perform the above reactions by a one-pot procedure from alcohols and nucleophiles. The reaction of thus formed 1, DMBQ and carboxylic acids or phenols afforded the corresponding alkylated products, including hindered secondary and tertiary alkylated ones, in good to high yields at room temperature. In the case of using chiral secondary alcohols, the corresponding carboxylic acid alkyl esters were obtained as well in high yields with perfect inversion of stereochemistry by SN2 replacement.
- Shintou, Taichi,Kikuchi, Wataru,Mukaiyama, Teruaki
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p. 1645 - 1667
(2007/10/03)
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- Reductive esterification of aromatic aldehydes using Zn/Ac 2O/imidazole or Zn/Yb(OTf)3/(RCO)2O system
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Benzaldehydes are reduced by metallic zinc in the presence of Ac 2O and imidazole, giving the corresponding benzyl acetates in good yields. Reductive esterification of aromatic aldehydes is also carried out via gem-diacetoxy compounds. Carbonyl compounds are readily converted to the gem-diacyloxy compounds in excellent yields on treatment with 2molar amounts of acid anhydride and 10mol% of Yb(OTf)3 in MeCN at room temperature. Thus-formed diacyloxy compounds derived from aromatic aldehydes are reduced in situ by metallic zinc to afford the corresponding esters.
- Hirao, Toshikazu,Santhitikul, Sirida,Takeuchi, Hiroki,Ogawa, Akiya,Sakurai, Hidehiro
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p. 10147 - 10152
(2007/10/03)
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- Efficient esterification of carboxylic acids with alkyl halides catalyzed by fluoride ions in ionic liquids
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Ionic liquids based on 1,3-dialkylimidazolinium methanesulfonate have been used as efficient reusable reaction media in the esterification of several carboxylic acids with alkyl halides catalyzed by fluoride ions. The method has wide applicability, and it is mild and green; it is useful for the protection of acids, via ester formation, for alkali labile molecules.
- Brinchi,Germani,Savelli
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p. 6583 - 6585
(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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- Benzylation of carboxylic acids by oxidation-reduction condensation using quinones and benzyloxydiphenylphosphine
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Various carboxylic benzyl esters were obtained in high yields by way of oxidation-reduction condensation in which benzyloxydiphenylphosphine (BDPP), having been prepared easily from chlorodiphenylphosphine and benzyl alcohol, was treated with various carboxylic acids in the presence of 2,6-dimethyl-1,4-benzoquinone(DMBQ) under mild conditions.
- Mukaiyama, Teruaki,Shintou, Taichi,Kikuchi, Wataru
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p. 1126 - 1127
(2007/10/03)
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- N-nitrosamide-mediated ritter-type reactions. Part II - The operation of persistent steric and π*-acceptor agostic-type effects
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Benzyl cations were generated via thermolysis of N-benzyl-N-nitrosopivalamide in molten 2-R-substituted benzonitriles (R = MeO, Me, H, F, Cl, and Br). The corresponding N-2-R-benzonitrilium species, in contrast to their 4-R-benzonitrilium counterparts, underwent limited reaction with pivalate ion to form unsymmetrical diacylamines via rearrangement of their initial imidic anhydrides. The yield of diacylamines, though small, varied systematically with the nature of the R group in a manner suggesting the operation of interesting steric and/or electronic effects on the pivalate ion-nitrilium ion collapse. The ortho-substituent, though present on only one side of the benzonitrilium ion inhibits reaction at both sides via steric hindrance in the near-ground state and steric crowding in the transition state (a persistent steric effect). The proposed electronic effect involves a π*-acceptor agostic-type interaction between n or σ electrons (HOMO) and the π* system (LUMO) of the nitrilium ion. Additionally, in many cases, attack by water on the nitrilium ion occurred to a significantly larger extent than attack by the much more nucleophilic and positionally favored pivalate ion on the same species. This observation is interpreted in terms of the differences in the sizes and docking trajectories of both species with the nitrilium ion due to charge and charge distribution on both nucleophiles.
- Darbeau, Ron W.,Pease, Rebecca S.,Perez, Edson V.,Gibble, Rebekah E.,Ayo, Faith A.,Sweeney, Aaron W.
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p. 2146 - 2153
(2007/10/03)
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- Selective sulfonylation of arenes and benzoylation of alcohols using lithium perchlorate as a catalyst under neutral conditions
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Sulfonylation of aromatics with p-toluenesulfonyl chloride and benzoylation of alcohols with benzoyl chloride using lithium perchlorate as a catalyst is described. The remarkable selectivity under neutral conditions is an attractive feature of this method.
- Bandgar,Kamble,Sadavarte,Uppalla
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p. 735 - 738
(2007/10/03)
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- Mixed Tishchenko reaction over solid base catalysts
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Catalytic behaviors of solid base catalysts for mixed Tishchenko reactions were investigated to elucidate the activity- and selectivity-determining factors in active sites of the catalysts and molecular structures of the reactants. A mixture containing equal amounts of two kinds of aldehydes was allowed to react at 353 K. The aldehydes used were benzaldehyde, pivalaldehyde, and cyclopropanecar-baldehyde. For all the reactions, the catalytic activity of alkaline earth oxides increased in the order of BaO ? MgO 2O3, ZrO2, ZnO, γ-alumina, hydrotalcite, KF/alumina, and KOH/alumina, were all inactive for the mixed Tishchenko reaction of benzaldehyde and pivalaldehyde; not only crossed-condensation products but also self-condensation products hardly formed. Quantum chemical calculations of the positive charges on the carbonyl carbon atoms of aldehydes and the structure parameters of the active species for the ester formations account for the observed selectivities to four Tishchenko dimers. The selectivities to four Tishchenko dimers over MgO and CaO are determined primarily in the step of the nucleophilic addition of the active species (PhCH2O-, tBuCH2O-, and C3H5CH2O-) to the carbonyl carbon atoms of aldehydes. The reaction of the aldehyde having a more positively charged and sterically less-hindered carbonyl carbon atom with the active species having a less-hindered oxygen atom proceeds faster.
- Seki, Tsunetake,Kabashima, Hajime,Akutsu, Kazumasa,Tachikawa, Hiroto,Hattori, Hideshi
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p. 393 - 401
(2007/10/03)
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- Esterification of carboxylic acids catalyzed by in situ generated tetraalkylammonium fluorides
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Esterification of carboxylic acids with alkyl halides can be efficiently catalyzed by tetrabutylammonium fluoride (TBAF) generated in situ from tetrabutylammonium hydrogensulfate (TBAHSO4) and KF·2H2O in THF. The general applicability and the characteristic feature of this approach has been amply demonstrated.
- Ooi, Takashi,Sugimoto, Hayato,Doda, Kanae,Maruoka, Keiji
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p. 9245 - 9248
(2007/10/03)
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- The Darbeau-White-Gibble reaction: An N-nitrosoamide-mediated Ritter-type reaction. Part I. A study of electronic, steric, and orbital effects in the nucleophile1a
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Benzyl cations were generated via thermal decomposition of N-benzyl-N-nitrosopivalamide in molten 4-R-substituted benzonitriles (R = NH2, Me2N, MeO, Me, H, F, and CF3). In each case, the benzyl cation was intercepted competitively by pivalate ion to yield benzyl pivalate and by the benzonitriles to yield the corresponding N-4-R-benzonitrilium ion. The latter onium ions reacted with pivalate ion to form benzimidic anhydrides which rearranged to yield N-4-R-benzoyl-N-pivaloylbenzylamines (i.e. unsymmetrical diacylamines). The yield of diacylamines (maximum ~10.6% for R = H) is smaller than from the corresponding reactions in acetonitrile and varied systematically with the nature and location of the R group on the aromatic nucleus. Both electron-releasing and electron-withdrawing groups at the para position effected a diminution of the yield of diacylamine; indeed for R = NH2, no diacylamine was formed. ortho Substitution of the aromatic nucleus resulted in significantly diminished yields of diacylamine, as did nucleophilic attack on the nitrilium ion by pivalate rather than acetate. Thus, both electronic and steric effects in nucleophilic attack on the nitrilium carbon were observed. The ratios of counterion-derived product to solvent-derived product for both the first-formed benzyl cation and the less reactive benzonitrilium ion are similar. This observation is interpreted in terms of the intermediacy of nitrogenous entity-separated ion-pairs in these deaminations.
- Darbeau,Gibble,Pease,Bridges,Siso,Heurtin
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p. 1084 - 1090
(2007/10/03)
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- Synthetic studies toward diazonamide A. A novel approach for polyoxazole synthesis
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(equation presented) The indole-bisoxazole fragment of diazonamide A was prepared by a Chan-type rearrangement of a tertiary amide. This approach represents a remarkably direct strategy for polyoxazole synthesis.
- Wipf, Peter,Methot, Joey-Lee
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p. 1261 - 1263
(2007/10/03)
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- Highly powerful and practical acylation of alcohols with acid anhydride catalyzed by Bi(OTf)3
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Bi(OTf)3-catalyzed acylation of alcohols with acid anhydride was evaluated in comparison with other acylation methods. The Bi(OTf)3/acid anhydride protocol was so powerful that sterically demanding or tertiary alcohols could be acylated smoothly. Less reactive acylation reagents such as benzoic and pivalic anhydride are also activated by this catalysis. In these cases, a new technology was developed in order to overcome difficulty in separation of the acylated product from the remaining acylating reagent: methanolysis of the unreacted anhydride into easily separable methyl ester realized quite easy separation of the desired acylation product. The Bi(OTf)3/acid anhydride protocol was applicable to a wide spectrum of alcohols bearing various functionalities. Acid-labile THP- or TBS-protected alcohol, furfuryl alcohol, and geraniol could be acylated as well as base-labile alcohols. Even acylation of functionalized tertiary alcohols was effected at room temperature.
- Orita,Tanahashi,Kakuda,Otera
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p. 8926 - 8934
(2007/10/03)
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- Reaction of essentially free benzyl cations with acetonitrile; synthesis of ethanimidic carboxylic anhydrides and unsymmetrical diacylamines
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Benzyl cations were generated via the thermal decomposition of N-benzyl- N-nitrosopivalamide in acetonitrile and acetonitrile-water mixtures at 25 °C. The first-formed (primary) benzylating agent, the benzyl cation, was scavenged competitively by pivalate (trimethyl acetate) ion to yield benzyl pivalate, by acetonitrile to yield the corresponding N-benzylnitrilium ion, and by water (when present) to yield benzyl alcohol. The nitrilium ion underwent a cascade of reactions to yield an array of products whose identities and relative yields as a function of time were used to elucidate the mechanistic paths involved. Thus, the N-benzylnitrilium ion reacted with pivalate ion to yield the Z-isomer of N-benzylethanimidic pivalic anhydride, followed by its conversion into the E-isomer. This article appears to be the first to document compounds of this type. The E-isomer is labile under the reaction conditions, rearranging into N-acetyl-N-pivalylbenzylamine. In the presence of water as a diluent, a significant fraction of the nitrosoamide was hydrolyzed to benzyl alcohol; hydrolysis of the nitrilium ion yielded N- benzyl acetamide. The yield of hydrosylates was directly proportional to the mole fraction of water in the medium.
- Darbeau, Ron W.,White, Emil H.,Nunez, Nicholas,Coit, Brian,Daigle, Mark
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p. 1115 - 1120
(2007/10/03)
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- 1-(2,5-dichlorophenyl)-2,2-bis(methylsulfanyl)vinyl esters as highly efficient chemoselective acylating reagents
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1-(2,5-Dichlorophenyl)-2,2-bis(methylsulfanyl)vinyl esters 4f-k were prepared in yields usually greater than 90%, by reacting acyl chlorides with 1-(2,5-dichlorophenyl)-2,2-bis(methylsulfanyl)ethanone enolate. These esters were demonstrated to be excellent chemoselective reagents for the acylation of amines, alcohols, thiols, pyrrole and indole. From all the acylation reactions the dimethyl α-oxo dithioacetal 2d, recyclable for the preparation of esters 4f-k, could be recovered in 90-100% yield.
- Degani,Dughera,Fochi,Serra
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p. 1200 - 1208
(2007/10/03)
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- Generation of allylic and benzylic organolithium reagents from the corresponding ester, amide, carbonate, carbamate and urea derivatives
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The reaction of different allylic and benzylic non-enolisable esters or amides (1), carbonates (4), carbamates (6, 7) and ureas (8) with an excess of lithium powder and a catalytic amount of naphthalene (10%) in the presence of an electrophile [(i)PrCHO, (t)BuCHO, PhCHO, Me2CO, Et2CO, (CH2)5CO, Ph2CO, Me3SiCl] in THF at different temperatures (-78, -30 or 0°C) leads, after hydrolysis with water to the corresponding allylated or benzylated products (2).
- Alonso, Emma,Guijarro, David,Martinez, Pedro,Ramon, Diego J.,Yus, Miguel
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p. 11027 - 11038
(2007/10/03)
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- P(RNCH2CH2)3N: Efficient catalysts for transesterifications, acylations, and deacylations
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Extremely strong nonionic superbases of the type P(RNCH2CH2)3N catalyze the transesterification of carboxylic acid esters with high selectivity and yields at 25 °C. These bases also catalyze the deacetylation of alcohols under mild conditions in quantitative yields. Using enol acetates as acylating agents, primary and secondary alcohols are efficiently protected as acetates through the action of these catalysts. Substituents such as epoxide, carbamate, acetal, oxazoline, nitro, and alkynyl functionalities are tolerated under the reaction conditions. N-Protected peptides undergo clean transesterification without significant racemization, making this methodology potentially very useful.
- Ilankumaran, Palanichamy,Verkade
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p. 3086 - 3089
(2007/10/03)
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- Esterification of carboxylic acids with alcohols by 4-(4,6-dimethoxy- 1,3,5-triazin-2-yl)-4-methyl-morpholinium chloride (DMTMM)
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Reaction of carboxylic acids with DMTMM in methanol, ethanol, or isopropyl alcohol in the presence of N-methylmorpholine affords the corresponding esters. The esterification can take place with an equimolar alcohol in THF.
- Kunishima, Munetaka,Morita, Jun,Kawachi, Chiho,Iwasaki, Fumiaki,Terao, Keiji,Tani, Shohei
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p. 1255 - 1256
(2007/10/03)
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- 4-(4,6-Dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride: An efficient condensing agent leading to the formation of amides and esters
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4-(4,6-Dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMTMM) was quantitatively synthesized by the coupling of 2-chloro-4,6-dimethoxy-1,3,5-triazine (CDMT) and N- methylmorpholine (NMM) in THF, and characterized. Condensation of carboxylic acids and amines by DMTMM proceeded effectively in THF to give the corresponding amides in good yields. The corresponding esters can be obtained by esterification of carboxylic acids with DMTMM in methanol, ethanol, isopropyl alcohol, or t-butyl alcohol in the presence of NMM. The amount of alcohols can be reduced to a stoichiometric amount by conducting the reaction in THF. Since the reactions proceed under atmospheric conditions without drying of the solvent, and the co- product (4,6-dimethoxy-1,3,5-triazin-2(1H)-one) arising from DMTMM after condensation can be readily removed by extraction, this method is a very practical one.
- Kunishima, Munetaka,Kawachi, Chiho,Morita, Jun,Terao, Keiji,Iwasaki, Fumiaki,Tani, Shohei
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p. 13159 - 13170
(2007/10/03)
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- Transesterification of N-acyloxazolidinones with alcohol by lanthanum(III) iodide
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Transesterification of N-acyloxazolidinones by treatment with an alcohol and lanthanum(III) iodide gives the corresponding esters in good to excellent yields under mild conditions with negligible racemization.
- Fukuzawa, Shin-Ichi,Hongo, Yuki
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p. 3521 - 3524
(2007/10/03)
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- Zinc promoted mild and efficient method for the esterification of acid chlorides with alcohols
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The esterification of variety of acid chlorides with alcohols in the presence of zinc is described. The easy formation of t-butyl and pivaloyl esters are the additional importance of this procedure.
- Yadav,Reddy, Gondi Sudershan,Srinivas, Dale,Himabindu, Konuru
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p. 2337 - 2342
(2007/10/03)
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- Convenient synthesis of benzyl and allyl esters using benzyl and allyl 2,2,2-trichloro-acetimidate
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Benzyl and allyl 2,2,2-trichloroacetimidate are efficient reagents for the preparation of benzyl and allyl esters of carboxylic acids in the presence of a catalytic amount of boron trifluoride-diethyl ether complex.
- Kokotos, George,Chiou, Antonia
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p. 168 - 170
(2007/10/03)
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- Photochemistry of substituted benzyl acetates and benzyl pivalates: A reinvestigation of substituent effects
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The photosolvolysis reactions, in methanol, of six substituted benzyl acetates (7a-f) and benzyl pivalates (8a-f) were studied. Five major benzylic products were formed from two critical intermediates. The ethers (9) were formed from the ion pair, 15, and all of the other products (10-14) were formed from the radical pair, 16. Quenching studies showed that only excited singlet state reactivity was important. The product yields were found to be highly substituent dependent. For instance, for the acetate esters, the yield of ether (9) varied from 2% for X = 4-OCH3 to 32% for X = 3-OCH3. Most of the differences in the yields could be attributed to ground state processes that occur after bond cleavage. The important competition is between electron transfer, converting the radical pair to the ion pair, and decarboxylation of RCO2*. The rates of electron transfer are shown to fit Marcus theory in both the normal and inverted regions. Direct heterolytic cleavage to form the ion pair is of minimal importance.
- Hilborn,MacKnight,Pincock,Wedge
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p. 3337 - 3346
(2007/10/02)
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- A novel, general route to the synthesis of carboxylic acid esters and thiolesters
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Carboxylic acids were conveniently esterified with alcohols and thiols by the use of triphenylphosphine and N-bromo/Iodo succinimide to afford the corresponding esters and thiol esters.
- Sucheta,Reddy,Ravi,Rama Rao
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p. 4415 - 4416
(2007/10/02)
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- Selective esterification reaction involving hexaalkyl guanidinium chloride catalyst
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A new efficient and selective esterification reaction of carboxylic acids with chloroformates is described using silica-supported catalyst (PBGSiCl). The chemioselectivity of the reaction was high particularly for sterically hindered carboxylic acids supported by a single pathway reaction.
- Gros,Le Perchec,Gauthier,Senet
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p. 1835 - 1842
(2007/10/02)
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