- New highly active and selective heterogeneous catalytic system for the synthesis of unsymmetrical organic carbonates: A green protocol
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A green, efficient, and selective synthesis of unsymmetrical organic carbonates is realised in the liquid phase by direct condensation of an alcohol and diethyl carbonate, in an ecocompatible route, in the presence of a recyclable heterogeneous solid-base CsF/α-Al2O3 catalyst. The catalyst displayed unprecedented activity after activation at 393 K for 4 h and produced quantitative yields with a greater rate compared with solid bases reported so far. The present process is a potential alternative to replace soluble bases in commercial synthesis. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005.
- Veldurthy, Bhaskar,Clacens, Jean-Marc,Figueras, Francois
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- An efficient synthesis of organic carbonates: Atom economic protocol with a new catalytic system
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Selective and solvent free synthesis of unsymmetrical organic carbonates catalysed by a reusable MgLa mixed oxide is achieved for the first time via direct condensation of an alcohol and diethyl carbonate in economic route with excellent yields.
- Veldurthy, Bhaskar,Figueras, Francois
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- Palladium-catalysed coupling between allyl carbonates and triethyl methanetricarboxylate (TEMT)
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Triethyl methanetricarboxylate (TEMT) is allylated by allylic carbonates in the presence of catalytic amounts of Pd(0) complexes; the reaction, conducted in very mild conditions, is fast and gives high yields of the title products.
- Cravotto, Giancarlo,Giovenzana, Giovanni B.,Sisti, Massimo,Palmisano, Giovanni
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- Stereoselective Modification of N-(α-Hydroxyacyl)-glycinesters via Palladium-Catalyzed Allylic Alkylation
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N-(α-Hydroxyacyl)-glycinesters can be used as excellent nucleophiles in Pd-catalyzed allylic alkylation. The method allows for the stereoselective introduction of a wide range of side chains, including highly functionalized ones. Both diastereomers can be accessed through variation of the reaction conditions. Furthermore, the use of stannylated carbonates introduces vinylstannane motifs, which are eligible for subsequent C-C coupling reactions.
- Horn, Alexander,Kazmaier, Uli
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supporting information
p. 4595 - 4599
(2019/06/27)
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- Tandem Palladium and Isothiourea Relay Catalysis: Enantioselective Synthesis of α-Amino Acid Derivatives via Allylic Amination and [2,3]-Sigmatropic Rearrangement
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A tandem relay catalytic protocol using both Pd and isothiourea catalysis has been developed for the enantioselective synthesis of α-amino acid derivatives containing two stereogenic centers from readily accessible N,N-disubstituted glycine aryl esters and allylic phosphates. The optimized process uses a bench-stable succinimide-based Pd precatalyst (FurCat) to promote Pd-catalyzed allylic ammonium salt generation from the allylic phosphate and the glycine aryl ester. Subsequent in situ enantioselective [2,3]-sigmatropic rearrangement catalyzed by the isothiourea benzotetramisole forms syn-α-amino acid derivatives with high diastereo- and enantioselectivity. This methodology is most effective using 4-nitrophenylglycine esters and tolerates a variety of substituted cinnamic and styrenyl allylic ethyl phosphates. The use of challenging unsymmetrical N-allyl-N-methylglycine esters is also tolerated under the catalytic relay conditions without compromising stereoselectivity.
- Spoehrle, Stéphanie S. M.,West, Thomas H.,Taylor, James E.,Slawin, Alexandra M. Z.,Smith, Andrew D.
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supporting information
p. 11895 - 11902
(2017/09/07)
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- Ketenimines from Isocyanides and Allyl Carbonates: Palladium-Catalyzed Synthesis of β,γ-Unsaturated Amides and Tetrazoles
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The reaction of allyl ethyl carbonates with isocyanides in the presence of a catalytic amount of Pd(OAc)2provided ketenimines through β-hydride elimination of the allyl imidoylpalladium intermediates. The insertion of the isocyanide into the π-allyl Pd complex proceeded via an unusual η1-allyl Pd species. The resulting ketenimines were hydrolyzed to β,γ-unsaturated carboxamides during purification by flash column chromatography on silica gel or converted in situ into 1,5-disubstituted tetrazoles by [3+2] cycloaddition with hydrazoic acid or trimethylsilyl azide.
- Qiu, Guanyinsheng,Mamboury, Mathias,Wang, Qian,Zhu, Jieping
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p. 15377 - 15381
(2016/12/06)
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- Catalytic activity of MCM-41-TBD in the selective preparation of carbamates and unsymmetrical alkyl carbonates from diethyl carbonate
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The synthesis of carbamates 3 and unsymmetrical alkyl carbonates 5 by reaction of diethyl carbonate with aliphatic amines or alcohols has been realized by using as heterogeneous catalyst a hybrid organic-inorganic material prepared by anchoring TBD to MCM-41 silica. Products are obtained in high yield and very good selectivity and the solid catalyst can be recovered simply by filtration and reused for different cycles without apparent lowering of activity. A supported N -carbethoxyguanidinium active intermediate is proposed, and some spectroscopic data are shown to support the mechanistic hypothesis.
- Carloni, Silvia,De Vos, Dirk E.,Jacobs, Pierre A.,Maggi, Raimondo,Sartori, Giovanni,Sartorio, Raffaella
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p. 199 - 204
(2007/10/03)
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- The synthesis of 5-substituted proline derivatives and of 5-substituted pyrrole-2-carboxylates by 5-endo cyclisations featuring a method for effectively favouring these with respect to 5-exo cyclisations
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Overall 5-endo cyclisations of the C-allylic glycine sulfonamides 5 lead to usually excellent yields of the 2,5-cis- or 2,5-trans-pyrrolidine-2-carboxylates 11 and 12 respectively, depending upon whether base is absent or present. While reductions to the corresponding pyrrolidine-2-methanols 13 proved efficient, subsequent eliminations of the elements of hydrogen iodide gave mixtures of products 14-16. Suitably positioned hydroxy groups compete successfully with the sulfonamide via a 5-exo cyclisation mode. However, when such a substrate contains a furan ring attached to the alkene function (21), then cyclisation does occur at the sulfonamide, presumably by participation of the furan oxygen, to give an iodopyrrolidine-2-methanol 13a. Finally, base-induced elimination of both hydrogen iodide and toluene-p-sulfinic acid from the initial iodopyrrolidines 11 and 12 leads to 5-substituted pyrrole-2-carboxylates 26. Overall, this sequence is complementary to the Kenner pyrrole synthesis.
- Knight,Redfern,Gilmore
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p. 2874 - 2883
(2007/10/03)
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- The Palladium-Catalyzed Cross-Coupling Reaction of Organosilicon Compounds with Allylic Carbonates or Diene Monoxides
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The cross-coupling reaction of allylic carbonates with organosilanes was found to proceed without fluoride ion activation under mild conditions by using a coordinatively unsaturated palladium complex as a catalyst.The reaction was assumed to proceed through an allylpalladium alkoxide derived from the allylic carbonate substrate and a palladium(0) species, the alkoxo ligand activating the organosilicon reagent.Likewise, diene monoxides also underwent cross-coupling with alkenyl- and arylfluorosilanes in moderate to high yields.
- Matsuhashi, Hayao,Asai, Satoshi,Hirabayashi, Kazunori,Hatanaka, Yasuo,Mori, Atsunori,Hiyama, Tamejiro
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p. 1943 - 1952
(2007/10/03)
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- Conversion of allylic alcohols into allylic nitromethyl compounds via a palladium-catalyzed solvolysis: An enantioselective synthesis of an advanced carbocyclic nucleoside precursor
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A two-step reaction sequence to homoallylic nitro compounds from allylic alcohols is presented. Ethoxy carbonylation of the alcohols with ethyl chloroformate provides the corresponding allylic ethyl carbonates in high yields. Exposure of these substrates to catalytic palladium(0) in CH3NO2 initiates a reaction sequence, ionization-decarboxylation-nitromethylation, that culminates with the formation of nitroalkenes. The regio- and stereochemical outcomes of the nitromethyl allylation reaction can be explained by the behavior of the transient π-allylpalladium complexes. This methodology serves as a centerpiece for the synthesis of an important carbocyclic nucleoside intermediate.
- Deardorff, Donald R.,Savin, Kenneth A.,Justman, Craig J.,Karanjawala, Zarir E.,Sheppeck II, James E.,Hager, David C.,Aydin, Nebil
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p. 3616 - 3622
(2007/10/03)
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- C-Allylation of L-Ascorbic acid under Palladium(0) Catalysis
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L-Ascorbic acid (1) is efficiently allylated at C-2 with primary and secondary allylic substrates by using palladium(0) catalysis.Hydrogenation of the resulting allylated compounds 6 affords L-ascorbic acid derivatives with saturated chains at C-2.
- Moreno-Manas, Marcial,Pleixats, Roser,Villarroya, Merce
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p. 4925 - 4928
(2007/10/02)
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- On the Regio- and Stereoselectivity of Bu4N-Catalyzed Allylic Alkylation
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Bu4N has been found to catalyze the alkylation of allylic carbonate with malonate anion.The reaction proceeds with good regioselectivity, the nucleophile attacking predominantly at the carbon where the leaving group was attached.Retention of configuration of the double bond during the course of reaction was observed.Alkylation of methyl (Z)-5-carbomethoxy-1-cyclohexen-3-yl carbonate with sodium salt of dimethyl malonate yielded dimethyl ((Z)-5-carbomethoxy-1-cyclohexen-3-yl)malonate in a highly stereoselective fashion, and a net retention of configuration at the center undergoing substitution is thus established.On the basis of regio- and stereochemical results, a reaction pathway involving an ?-allyliron complex has been suggested.
- Xu, Yuanyao,Zhou, Bo
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p. 974 - 977
(2007/10/02)
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