- Isopropyl 2-ethoxyacetate—an efficient acylating agent for lipase-catalyzed kinetic resolution of amines in batch and continuous-flow modes
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Productivity [conversion (c) and specific reaction rate (rbatchor rflow)] and enantiomer selectivity [enantiomeric ratio (E) and enantiomeric excess (ee) of the products] of ethyl and isopropyl esters of acetic, 2-methoxyacetic and 2-ethoxyacetic acids as acylating agents were compared in the N-acylation of (±)-1-phenylethanamine rac-1 catalyzed by variously immobilized forms of Candida antarctica lipase B (CaLB) using shake flasks and continuous-flow reactors. The effect of the temperature in the 0–80 °C range on productivity and enantiomer selectivity in KRs of rac-1 was investigated with the isopropyl esters in continuous-flow mode using CaLB-filled minireactors. Isopropyl 2-ethoxyacetate surpassed the performance of ethyl 2-methoxyacetate in terms of both productivity (1.9–2.9 times higher rate in batch mode) and enantiomeric selectivity (ee(R)-amide>99.9% compared to 99.8%) providing at 40 °C high volumetric productivity (2.22 kg L?1h?1), specific reaction rate and enantiomeric excess (rflow=783 μmol min?1g?1, ee(R)-2c>99.9%).
- Oláh, Márk,Boros, Zoltán,Hornyánszky, Gábor,Poppe, László
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p. 7249 - 7255
(2016/10/26)
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- A general and enantioselective approach to pentoses: A rapid synthesis of PSI-6130, the nucleoside core of sofosbuvir
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An efficient route towards biologically relevant pentose derivatives is described. The de novo synthetic strategy features an enantioselective α-oxidation reaction enabled by a chiral amine in conjunction with copper(II) catalysis. A subsequent Mukaiyama aldol coupling allows for the incorporation of a wide array of modular two-carbon fragments. Lactone intermediates accessed via this route provide a useful platform for elaboration, as demonstrated by the preparation of a variety of C-nucleosides and fluorinated pentoses. Finally, this work has facilitated expedient syntheses of pharmaceutically active compounds currently in clinical use.
- Peifer, Manuel,Berger, Rapha?lle,Shurtleff, Valerie W.,Conrad, Jay C.,Macmillan, David W. C.
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supporting information
p. 5900 - 5903
(2014/05/20)
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- Efficient and catalyst-free condensation of acid chlorides and alcohols using continuous flow
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An efficient, catalyst-free continuous flow procedure for the condensation of acid chlorides and alcohols was developed. Different esters could be obtained using this protocol with excellent conversions starting from the corresponding acid chlorides and alcohols in very short reaction times (5-7 min). The reaction was performed solventless for liquid reagents but requires a solvent for solid reagents in order to prevent clogging of the microreactor. Since no catalyst is needed, the purification of the reaction mixture is very straightforward. Scale-up of the reaction to a microreactor with an internal volume of 13.8 ml makes it possible to produce 2.2 g min-1 of ester with an isolated yield of 98% and recuperation of the formed HCl.
- Van Waes, Frederik E. A.,Cukalovic, A.,Stevens, Christian V.,Drabowicz, J.
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p. 2776 - 2779,4
(2020/09/14)
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- Fast DKR of amines using isopropyl 2-methoxyacetate as acyl donor
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The dynamic kinetic resolution (DKR) of various primary amine substrates was performed using a modified version of the Baeckvall system. A single equivalent of isopropyl 2-methoxyacetate was used as acyl donor in combination with p-MeO Shvo complex as the racemization catalyst and Novozym 435 as the acylation catalyst. A reaction temperature of 100°C was employed to ensure a high racemization rate. Adding 2,4-dimethyl-3-pentanol (DMP) as hydrogen donor at a concentration of 0.5 M successfully suppressed side product formation. Under these modified DKR conditions, complete conversion was observed for most substrates within 26 h showing both high ee values and good chemoselectivity, whereas the original system required a reaction time of 72 h. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.
- Veld, Martijn A. J.,Hult, Karl,Palmans, Anja R. A.,Meijer
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p. 5416 - 5421
(2008/03/18)
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- Method for the production of esters
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The present invention relates to a novel process for the preparation of esters of the general formula I from compounds of the general formula II contained in aqueous solutions which comprises a) extracting the compounds of the general formula II directly or after liberation from their salts in the presence of a C1-C8-alcohol and a water-immiscible solvent and b) then esterifying with the C1-C8-alcohol in the presence of a catalyst and of an entraining agent under the conditions of an azeotropic distillation, where the process steps (a) and (b) can be carried out separately in terms of time and space or else in a successive continuous or batchwise sequence and where the variables and substituents in the formulae I and II have the following meanings: R1=F, Cl, —OH, —OC1-C10-alkyl, R2=H, C1-C10-alkyl; R3=C1-C8-alkyl, Q=—OH, —O?K+, where K+is an alkali metal cation or alkaline earth metal cation, n=0, 1 or 2.
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Page column 11-12
(2008/06/13)
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- Process for the preparation of methoxyacetic acid esters
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The invention relates to a process for the preparation of methoxyacetic acid esters in which a chloroacetic acid ester is reacted with an alkali metal methoxide to give the methoxyacetic acid ester.
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- CATALYTIC ROLE OF DIORGANOTIN DICHLORIDE IN ESTERIFICATION OF CARBOXYLIC ACIDS
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Various carboxylic acids were converted into corresponding esters in fair to good yields by diorganotin dichloride-catalysed reaction with alcohols.
- Kumar, Amal K.,Chattopadhyay, Tapas K.
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p. 3713 - 3714
(2007/10/02)
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- Carbenes in a Rigid Matrix. Substituent Effects on the Temperature Dependence of α-Carbonylcarbene Reactions
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The temperature dependence of methoxycarbonyl- (1a and b) and benzoyl-carbenes (2a and b) reactions in alcohols has been examined in order to elucidate the scope and limitation of low temperature photolysis as a tool for detecting triplet carbenes.The results reveal that the method cannot be applied to all carbenes but gives important information on the reactivity and/or multiplicity of ground-state carbenes.Low-temperature photolysis of PhCN2CO2Me in an ethanol matrix, for example, resulted in a dramatic increase in C-H insertion products, probably derived from the triplet (1a) via an abstraction-recombination mechanism, at the expense of the singlet product, i.e. the O-H insertion compound, which was shown to be the main product of photolysis at ambient temperature.In marked contrast, (1b) generated in a propan-2-ol matrix at -196 deg C did not result in a major increase in the C-H insertion product.Similar and more contrasting substituent effects on the temperature dependence were observed in the benzoylcarbene system (2).Thus, the Wolff rearrangement of (2a) was almost completely supressed in a rigid matrix at -196 deg C, whereas that of (2b) was not appreciably supressed even at -196 deg C.These differences were explained by considering the effects of the substituent on the ground-state multiplicity of carbene and/or on the relation of the activation energy differences of the singlet and triplet reactions with energy differences between two states.
- Tomioka, Hideo,Okuno, Hiroshi,Izawa, Yasuji
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p. 1636 - 1641
(2007/10/02)
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- Mechanism of the Photochemical Wolff Rearrangement. The Role of Conformation in the Photolysis of α-Diazo Carbonyl Compounds.
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Investigation of photochemical processes of several α-diazo carbonyl compounds reveals that the Wolff rearrangement to form ketene takes place directly from the singlet excited state of the s-Z conformer whereas the excited state of the s-E conformer dissociates nitrogen to generate singlet carbonyl carbene, which either undergoes characteristic carbenic reactions, e.g., insertion and 1,2-hydrogen shift, or gives rise to ketene.The migratory aptitude as well as the relative efficiency of other competing reactions from singlet carbene is shown to be an important factor in dete rmining which reaction pathway is favored.Substantial amounts of singlet carbene can be formed even under sensitized conditions, presumably via intersystem crossing from initially formed triplet carbene.
- Tomioka, Hideo,Okuno, Hiroshi,Izawa, Yasuji
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p. 5278 - 5283
(2007/10/02)
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