- A highly selective, high-speed, and hydrolysis-free O-acylation in subcritical water in the absence of a catalyst
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(Chemical Equation Presented) Fast and furious: A wide range of alcohols are acylated by acetic anhydride, in the absence of catalyst, in subcritical water in a flow-type microreaction system. The esters are selectively produced in high yields at temperatures of 200 to 250°C. Varying the amount of acetic anhydride added with respect to the alcohols allows the regioselective acylation of one or both hydroxy groups of various dihydroxy compounds (see picture).
- Sato, Masahiro,Matsushima, Keiichiro,Kawanami, Hajime,Ikuhsima, Yutaka
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- N-Heterocyclic Carbene/Carboxylic Acid Co-Catalysis Enables Oxidative Esterification of Demanding Aldehydes/Enals, at Low Catalyst Loading
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We report the discovery that simple carboxylic acids, such as benzoic acid, boost the activity of N-heterocyclic carbene (NHC) catalysts in the oxidative esterification of aldehydes. A simple and efficient protocol for the transformation of a wide range of sterically hindered α- and β-substituted aliphatic aldehydes/enals, catalyzed by a novel and readily accessible N-Mes-/N-2,4,6-trichlorophenyl 1,2,4-triazolium salt, and benzoic acid as co-catalyst, was developed. A whole series of α/β-substituted aliphatic aldehydes/enals hitherto not amenable to NHC-catalyzed esterification could be reacted at typical catalyst loadings of 0.02–1.0 mol %. For benzaldehyde, even 0.005 mol % of NHC catalyst proved sufficient: the lowest value ever achieved in NHC catalysis. Preliminary studies point to carboxylic acid-induced acceleration of acyl transfer from azolium enolate intermediates as the mechanistic basis of the observed effect.
- Berkessel, Albrecht,Biswas, Animesh,Harnying, Wacharee,Sudkaow, Panyapon
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supporting information
p. 19631 - 19636
(2021/08/09)
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- Aerobic oxidative esterification and thioesterification of aldehydes using dibromoisocyanuric acid under mild conditions: No metal catalysts required
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A practical direct method for the direct preparation of esters and thioesters from aldehydes is described. Esters and thioesters were synthesized by oxidative esterification and thioesterification via in situ generated acyl bromide intermediates, which were used to react with various alcohols and thiols. The esterification and thioesterification were readily performed in the presence of dibromoisocyanuric acid in dichloromethane, without any metal catalysts and under mild conditions. By using this reaction protocol, various esters and thioesters were prepared in high yields. This effective method offers a promising approach for the facile esterification and thioesterification of aldehydes.
- Kwon, Young-Do,La, Minh Thanh,Kim, Hee-Kwon
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p. 10833 - 10841
(2018/07/05)
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- 1,4-Bis-Dipp/Mes-1,2,4-Triazolylidenes: Carbene Catalysts That Efficiently Overcome Steric Hindrance in the Redox Esterification of α- And β-Substituted α,β-Enals
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As reported by Scheidt and Bode in 2005, sterically nonencumbered α,β-enals are readily converted to saturated esters in the presence of alcohols and N-heterocyclic carbene catalysts, e.g., benzimidazolylidenes or triazolylidenes. However, substituents at the α- or β-position of the α,β-enal substrate are typically not tolerated, thus severely limiting the substrate spectrum. On the basis of our earlier mechanistic studies, a set of N-Mes- or N-Dipp-substituted 1,2,4-triazolium salts were synthesized and evaluated as (pre)catalysts in the redox esterification of various α- or β-substituted enals. In particular the 1,4-bis-Mes/Dipp-1,2,4-triazolylidenes overcome the above limitations and efficiently catalyze the redox esterification of a whole series of α/β-substituted enals hitherto not amenable to NHC-catalyzed transformations. The synthetic value of 1,4-bis-Mes/Dipp-1,2,4-triazolylidenes is further demonstrated by the one-step bicyclization of 10-oxocitral to (racemic) nepetalactone in diastereomerically pure form.
- Yatham, Veera Reddy,Harnying, Wacharee,Kootz, Darius,Neud?rfl, J?rg-M.,Schl?rer, Nils E.,Berkessel, Albrecht
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supporting information
p. 2670 - 2677
(2016/03/12)
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- Oxidation of primary aliphatic and aromatic aldehydes with difluoro(aryl)-λ3-bromane
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Oxidation of primary aliphatic aldehydes with p- trifluoromethylphenyl(difluoro)-λ3-bromane in dichloromethane at 0 °C afforded acid fluorides selectively in good yields, while that of aromatic aldehydes in chloroform at room temperature produced aryl difluoromethyl ethers. A larger migratory aptitude of aryl groups compared to primary alkyl groups during a 1,2-shift from carbon to an electron-deficient oxygen atom in bromane(III) Criegee-type intermediates will result in these differences in the reaction courses.
- Ochiai, Masahito,Yoshimura, Akira,Hoque, Md. Mahbubul,Okubo, Takuji,Saito, Motomichi,Miyamoto, Kazunori
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p. 5568 - 5571
(2011/12/03)
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- α-Aroyloxyaldehydes: Scope and limitations as alternatives to α-haloaldehydes for NHC-catalysed redox transformations
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α-Aroyloxyaldehydes are readily prepared bench stable synthetic intermediates. Their ability to act as α-haloaldehyde surrogates for NHC-promoted redox esterifications and in [4+2] cycloadditions is described.
- Ling, Kenneth B.,Smith, Andrew D.
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supporting information; experimental part
p. 373 - 375
(2011/02/24)
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- Efficient three-step sequence for the deamination of α-aminoesters. Application to the synthesis of CysLT1 antagonists
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A practical and efficient three-step sequence for the deamination of α-aminoesters is reported. This method is based on the NaBH4-mediated selective reduction of α-diazoesters to α-hydrazonoesters and has been successfully applied to the deamin
- González, Alfredo,Pérez, Daniel,Puig, Carles,Ryder, Hamish,Sanahuja, Jordi,Solé, Laia,Bach, Jordi
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supporting information; experimental part
p. 2750 - 2753
(2009/09/25)
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- Process for producing esterificated condensate
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The present invention provides a method for preparing ester or thioester that can conduct catalytic esterification reaction with an equimolar amount of carboxylic acid and alcohol, or catalytic thioesterification reaction with carboxylic acid and an equimolar amount or small amount of thiol, and can be expected as an industrial method that needs an enormous amount of synthesis in the light of green chemistry. By using hafnium chloride (IV), especially tetravalent hafnium compounds represented by hafnium chloride (IV)?(THF)2 or hafnium (IV)t-butoxide as a (poly) condensation catalyst, direct condensation reaction is conducted from carboxylic acid and an equimolar amount of alcohol or a little smaller amount of thiol, in the nonpolar solvent such as toluene and the like, in a deoxidization atmosphere and under heating reflux, and the reaction synthesizes ester monomer or thioester monomer, polyester or polythioester. When heating reflux is conducted by using a nonpolar solvent, it is preferable to remove azeotropic water from the reaction system.
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- Direct ester condensation from a 1:1 mixture of carboxylic acids and alcohols catalyzed by hafnium(IV) or zirconium(IV) salts
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To promote atom efficiency in synthesis and to avoid the generation of environmental waste, the use of stoichiometric amounts of condensing reagents or excess substrates should be avoided. In esterification, excess amounts of either carboxylic acids or alcohols are normally needed. We found that the direct condensation of equimolar amounts of carboxylic acids and alcohols could be achieved using hafnium(IV) or zirconium(IV) salts. These metal salts are highly effective as catalysts for the selective esterification of primary alcohols with carboxylic acids in the presence of secondary alcohols or aromatic alcohols. The present methods can be applied to direct polyesterification and may be suitable for large-scale operations.
- Ishihara, Kazuaki,Nakayama, Masaya,Ohara, Suguru,Yamamoto, Hisashi
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p. 8179 - 8188
(2007/10/03)
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- CHLORO- AND IODOTRIMETHYLSILANE-ACTIVATED ADDITIONS OF ORGANOCOPPER COMPOUNDS TO ENONES AND ENOATES
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Organocopper compounds add to enones and enoates in the presence of chloromethylsilane in ether giving the conjugate adducts in preparatively usefu yields via the silyl enol ethers.Presence of lithium iodide is important and excess of chlorotrimethylsilane accelerates the reactions.The combination of organocopper compound, iodotrimethylsilane and dimethyl sulfide gave faster reactions and very high yields, particularly in dichloromethane, where the reaction mixtures gradually became homogeneous.
- Bergdahl, Mikael,Lindstedt, Eva-Lotte,Nilsson, Martin,Olsson, Thomas
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p. 2055 - 2062
(2007/10/02)
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- Action of Lewis Acids on Aromatic Acetals
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Acetals of the type X.C6H4CH(OR)2, where R = Et, n-Bu and isoamyl, and X = H and CH3, react with antimony perchloride and ferric chloride in anhydrous 1,2-dichloroethane to give benzyl alkyl ether, alkyl benzoate, benzyl ester, α,β-unsaturated aldehyde, benzaldehyde and a small quantity of benzyl alcohol. p-Nitrobenzaldehyde di-n-butyl acetal gave only p-nitrobenzaldehyde and a trace of p-nitrobenzyl alcohol.The mechanism of the formation of benzyl alkyl ether is explained by a hydride ion transfer and that of α,β-unsaturated aldehyde by an aldol type of condensation.The aliphatic and aromatic aldehydes produced in the reaction could undergo Tischenko reaction in the presence of antimony or iron alkoxides to give the esters.
- Alphonse, I.,Arulraj, S. J.
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p. 820 - 822
(2007/10/02)
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- KINETICS AND MECHANISM OF THE ADDITION OF ALCOHOLS TO KETENES IN DIETHYL ETHER SOLUTION IN THE PRESENCE OF BORON TRIFLUORIDE
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The kinetics are reported of the boron trifluoride-catalysed additions of seven alcohols to dimethylketene in diethyl ether solution at 25 deg C.All the reactions involve the rapid initial formation of 1:1 alcohol-boron trifluoride adduct (formation constant K) which transfer a proton to the ketene in the slow step of the addition.For t-butyl alcohol, ethanol, methanol, phenylmethanol, and 2-chloroethanol the K values are > 1000, 320+/-50, 300+/-50, 80+/-20, and 65+/-15 l/mol, respectively.The more acididc an alcohol the faster is the reaction of its 1:1 boron trifluoride adduct with the ketene.For t-butyl alcohol the relatively slow reaction of its adduct is catalysed by a further molecule of the adduct and by free boron trifluoride.At 25 deg C the spontaneous addition of ethanol to diphenylketene in ether (like that to dimethylketene) is first order in the ketene and third order in the ethanol concentration.In this reaction diphenylketene is ca. 10-fold more reactive than the dimethyl derivative in the concentration range studied.Whereas the addition of boron trifluoride to the solution catalyses the addition of ethanol (and the other alcohols) to dimethylketene to such an extent that the spontaneous addition makes a negligible contribution to the overall rate, with diphenylketene the alcohol-boron trifluoride adduct is relatively so unreactive that added boron trifluoride strongly inhibits the spontaneous addition.The ethanol-boron trifluoride adducts is > 10E4-fold less reactive towards diphenylketene.These results support our previous conclusions concerning additions of acidic species to ketenes.
- Poon, Nai L.,Satchell, Derek P. N.
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p. 1083 - 1088
(2007/10/02)
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