- Meta -selective arene C-H bond olefination of arylacetic acid using a nitrile-based directing group
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A nitrile-based template attached with a phenylacetic acid framework promoted meta-selective C-H bond olefination. This palladium-catalyzed protocol is applicable to a wide range of substituted phenylacetic acids and tolerates a variety of functional groups. The versatility of this operationally simple method has been demonstrated through drug diversification.
- Bera, Milan,Modak, Atanu,Patra, Tuhin,Maji, Arun,Maiti, Debabrata
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- Lipase-catalyzed 1,6-acylation of D-mannitol
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The selective synthesis of 1,6-diacyl D-mannitols from 2,2,2-trifluoroethyl esters using transesterification, catalyzed by lipases, has been investigated, and the results have been compared with those obtained from a typical acid chloride procedure and a
- Duggan, Peter J.,Humphrey, David G.,McCarl, Victoria
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- Kinetic Analysis as an Optimization Tool for Catalytic Esterification with a Moisture-Tolerant Zirconium Complex
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This work describes the use of kinetics as a tool for rational optimization of an esterification process with down to equimolar ratios of reagents using a recyclable commercially available zirconocene complex in catalytic amounts. In contrast to previously reported group IV metal-catalyzed esterification protocols, the work presented herein circumvents the use of water scavengers and perfluorooctane sulfonate (PFOS) ligands. Insights into the operating mechanism are presented.
- Dalla-Santa, Oscar,Lundberg, Helena,Szabó, Zoltán,Villo, Piret
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p. 6959 - 6969
(2020/06/27)
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- Cu(I)/chiral bisoxazoline-catalyzed enantioselective sommelet-hauser rearrangement of sulfonium ylides
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Catalytic asymmetric thia-Sommelet-Hauser rearrangement of sulfonium ylides remains a great challenge due to its multistep reaction mechanism involving metal carbene formation, proton transfer, and [2,3]-sigmatropic rearrangement. In particular, the key problem of such reactions is the differentiation of the enantiotopic lone pair electrons of sulfur, which generates the sulfonium ylide intermediate bearing chirality on the sulfur atom. With a modified chiral bisoxazoline ligand, we developed a Cu(I)- catalyzed asymmetric thia-Sommelet-Hauser rearrangement with good to excellent enantioselectivities. Mechanistic studies provide insights into the details of the reaction mechanism.
- Wang, Jianbo,Li, Shu-Sen
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supporting information
p. 12343 - 12358
(2020/11/10)
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- Evaluating aryl esters as bench-stable C(1)-ammonium enolate precursors in catalytic, enantioselective Michael addition-lactonisations
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An evaluation of a range of aryl, alkyl and vinyl esters as prospective C(1)-ammonium enolate precursors in enantioselective Michael addition-lactonisation processes with (E)-trifluoromethylenones using isothiourea catalysis is reported. Electron deficient aryl esters are required for reactivity, with 2,4,6-trichlorophenyl esters providing optimal product yields. Catalyst screening showed that tetramisole was the most effective isothiourea catalyst, giving the desired dihydropyranone product in excellent yield and stereoselectivity (up to 90 : 10 dr and 98 : 2 er). The scope and limitations of this process have been evaluated, with a range of diester products being generated after ring-opening with MeOH to give stereodefined dihydropyranones with excellent stereocontrol (10 examples, typically ~90 : 10 dr and >95 : 5 er).
- Young, Claire M.,Taylor, James E.,Smith, Andrew D.
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supporting information
p. 4747 - 4752
(2019/05/24)
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- Direct Esterification of Carboxylic Acids with Perfluorinated Alcohols Mediated by XtalFluor-E
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The direct esterification of carboxylic acids with perfluorinated alcohols mediated by XtalFluor-E is reported. The corresponding polyfluorinated esters are obtained in moderate to excellent yields with a broad range of carboxylic acids, including aromati
- Vandamme, Mathilde,Bouchard, Léa,Gilbert, Audrey,Keita, Massaba,Paquin, Jean-Fran?ois
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supporting information
p. 6468 - 6471
(2016/12/23)
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- Synthesis of arylacetates from benzylic alcohols and oxalate esters through decarboxylative coupling
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Follow that dream: By combining a reversible transesterification between benzylic alcohols and dialkyl oxalates with catalytic decarboxylation of the resulting esters, a regiospecific C-C-bond-forming reaction to give α-arylacetates was achieved. In the overall process, CO2 and a volatile alcohol are the only byproducts. Various α-arylacetates were thus synthesized in high yields from easily accessible starting materials in the presence of catalytic amounts of Pd(OAc)2, dppp, and DABCO (see scheme). Copyright
- Gruenberg, Matthias F.,Goossen, Lukas J.
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supporting information
p. 7334 - 7337
(2013/06/27)
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- Structure-Activity Relationships in the Esterase-catalysed Hydrolysis and Transesterification of Esters and Lactones
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The Broensted exponents for the alkaline hydrolysis of alkyl esters are 1.3 and 0.4 for substitution in the acyl and alcohol portions, respectively, which is indicative of a transition state which resembles the anionic tetrahedral intermediate with a localised negative charge.By contrast, the rate of the pig liver esterase (PLE)-catalysed hydrolysis shows little dependence upon the electron-withdrawing power of substituents.The values of kcat are independent of the pKa of the leaving group alcohol suggesting rate-limiting deacylation.There is a small steric effect of α-substitution in both the alcohol and carboxylic acid residues for the enzyme-catalysed reactions but the enzyme rate enhancement factor remains high for most esters.There is no substantial ee observed for the hydrolysis of racemic esters although the kinetic data can be used for determining the regioselective hydrolysis of diesters.Unsubstituted lactones are poor substrates for PLE but derivatives with hydrophobic substituents show kcat/Km values similar to those for acyclic esters.Dihydrocoumarin undergoes transesterification catalysed by PLE, kcat increases with increasing alcohol concentration indicative of rate-limiting deacylation.There is enantioselectivity in the PLE-catalysed hydrolysis of some racemic lactones but little or none in the transesterification of racemic alcohols with dihydrocoumarin.
- Barton, Patrick,Laws, Andrew P.,Page, Michael I.
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p. 2021 - 2030
(2007/10/02)
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- Acid-Catalyzed Reaction of 2,2,2-Trifluorodiazoethane for Analysis of Functional Groups by 19F Nuclear Magnetic Resonance Spectrometry
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The acid-catalyzed reactions of trifluorodiazoethane with alcohols, phenols, thiols, and carboxylic acids are reported.The yield data for these trifluoroethyl derivatives suggest a simple, and in many cases, quantitative method for introduction of a fluorine tagging group.The 19F chemical shifts indicate that most functional groups (e.g., phenols, alcohols, etc.) have fairly well resolved chemical shifts regions.In addition, paramagnetic shift reagents have been utilized to selectively differentiate carboxylic acids from other active hydrogen functional groups.
- Koller, K. L.,Dorn, H. C.
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p. 529 - 533
(2007/10/02)
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