- Exocyclic iminium salts as catalysts for alkene epoxidation by Oxoneρ
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Exocyclic iminium salts are evaluated as catalysts for alkene epoxidation by Oxone, presumed to proceed via the corresponding oxaziridinium species. Iminium triflate salts derived from pyrrolidine and electron poor aromatic aldehydes were found to be good catalysts. Attempts to prepare chiral variants of these iminium salts were largely unsuccessful, presumably due to their ready hydrolysis.
- Armstrong, Alan,Ahmed, Ghafoor,Garnett, Ian,Goacolou, Katell,Wailes, J. Steven
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- Design of efficient ketone catalysts for epoxidation by using the field effect
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By using the field effect (through-space charge-dipole or dipole-dipole interactions), efficient ketone catalysts 7 and 10 were developed for in situ epoxidation of olefins with Oxone. With either ketone 7 (10-20 mol %) or 10 (5-10 mol %) as catalyst, epoxidation of various olefins (2 mmol scale) at room temperature with 1.5 equiv of Oxone was complete in a short period of time with excellent isolated yields of epoxides (80-97%) and good ketone recovery (~80%) Furthermore, the in situ epoxidation of olefins can be performed on a large scale (20-100 mmol) directly with 5 mol % of commercially available tetrahydrothiopyran-4-one, which is oxidized by Oxone to ketone 10 during the epoxidation reactions.
- Yang, Dan,Yip, Yiu-Chung,Jiao, Guan-Sheng,Wong, Man-Kin
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- Formation of epoxides and N-arylaziridines via a simple Mg-Barbier reaction in DMF
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The Mg-activation of benzal bromide 2b in DMF in the presence of carbonyl compounds 1 or imines 4 leads to epoxides 3 and N-arylaziridines 5, respectively, with acceptable isolated yields. It was found that DMF is likely involved in this process to form a nucleophilic intermediate by reaction with a first generated electrophilic carbene. Results obtained in this chemical approach are compared to those obtained using electrochemical activation, also in DMF.
- Oudeyer, Sylvain,Léonel, Eric,Paugam, Jean Paul,Nédélec, Jean-Yves
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- An effective dual copper-and sulfide-catalytic system for the epoxidation of aldehydes with phenyldiazomethane
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Epoxides have been obtained from alde-hydes and phenyldiazomethane using catalytic amounts of both the copper homoscorpionate com-plexes Tp xCuL (Tpx = homoscorpionate ligand; L = acetonitrile or tetrahydrofuran, THF) and dimethyl sulfide (SMe2) in high yields and diasteroselectivities, and with activities higher (TOF = 46 h-1) than those already known with rhodium-or copper-based cata-lysts. Among the copper(I) homoscorpionate com-plexes tested, TpBr3Cu(NCCH 3) showed the highest catalytic activity under mild conditions. The catalytic activity is controlled by electronic effects induced by the Tp x ligand as well as by the stability of the TpxCu(SR 2) adducts. Indeed, in the case of TpMs as ligand, the TpMsCu(THT) (THT = tetrahydrothio-phene) and Tp MsCu(SMe2) species could be isolated as very stable crystalline solids, the molecular struc-ture of the former being confirmed by single-crystal X-ray diffraction analysis. The in situ generation of PhCHN 2 from benzaldehyde tosylhydrazone sodium salt at 60 °C in methyl tert-butyl ether as solvent and TpMsCu(THF) as the catalyst also showed high cata-lytic activities, improving those already reported with copper-based catalysts.
- Pereira, Ana,Martín, Carmen,Maya, Celia,Belderrain, Tomás R.,Pérez, Pedro J.
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- Non-aqueous iminium salt mediated catalytic asymmetric epoxidation
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A range of substituted dihydroisoquinolinium salts has been tested in the catalytic asymmetric epoxidation of simple alkenes using our newly developed non-aqueous conditions employing tetraphenylphosphonium monoperoxysulfate (TPPP) as oxidant, giving ees of up to 97%.
- Bulman Page, Philip C.,Buckley, Benjamin R.,Barros, David,Blacker, A. John,Heaney, Harry,Marples, Brian A.
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- N,N-Dialkylalloxans - a new class of catalyst for dioxirane epoxidations
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N,N-Dimethyl- and N,N-dibenzylalloxans 1a and 1b have been prepared and used as novel dioxirane catalysts for the epoxidation of a range of di- and tri-substituted alkenes in good to excellent yield. The dibenzylalloxan 1b can be recovered in high yield with no evidence of catalyst decomposition.
- Carnell, Andrew J.,Johnstone, Robert A. W.,Parsy, Christophe C.,Sanderson, William R.
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- Highly efficient catalysts for epoxidation mediated by iminium salts
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A range of substituted dihydroisoquinolinium salts has been tested in the catalytic epoxidation of several alkenes. Catalyst loadings as low as 0.5 mol% have been used in the epoxidation of 1-phenylcyclohexene. Georg Thieme Verlag Stuttgart.
- Bulman Page, Philip C.,Buckley, Benjamin R.,Appleby, Louise F.,Alsters, Paul A.
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- First Epoxidation Reaction of Carbonyl Compounds via Ferrocenyl Sulfur Ylides
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Epoxidation reactions of carbonyl compounds (aldehydes and a ketone) mediated by sulfanyl ferrocenes have been successfully achieved in a one-pot reaction, under mild conditions. This reaction implies intermediary formation of a sulfonium salt (a ferrocenyl one was observed for the first time by 1H NMR) and then an ylide. The diastereoselectivity of the formation of stilbene oxide was unusual: the effect of steric hindrance and aromatic nature of the sulfide substituents have been evidenced. A catalytic asymmetric example with a planar chiral ferrocene is described.
- Miniere, Stephanie,Reboul, Vincent,Arrayas, Ramon Gomez,Metzner, Patrick,Carretero, Juan Carlos
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- A biomimetic iron catalyst for the epoxidation of olefins with molecular oxygen at room temperature
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It's no sacrifice: A bio-inspired iron system, in which a β-keto ester serves as a sacrificial cosubstrate, readily epoxidizes olefins under ambient conditions with air. Aromatic olefins are oxidized in high yields with excellent chemoselectivity. Mechanistic investigations point out substantial differences to well-known radical-based autoxidations.
- Schroeder, Kristin,Join, Benoet,Amali, Arlin Jose,Junge, Kathrin,Ribas, Xavi,Costas, Miquel,Beller, Matthias
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- Pyrrolidine-Derived Iminium Salts as Catalysts for Alkene Epoxidation by Oxone
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Iminium triflate salts derived from pyrrolidine and aromatic aldehydes catalyse alkene epoxidation by Oxone. Catalysts 3d and 3e, with ortho-electron withdrawing substituents, are most effective.
- Armstrong, Alan,Ahmed, Ghafoor,Garnett, Ian,Goacolou, Katell
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- Manganese salen compounds embedded within cross-linked chiral polyethylenimine: Asymmetric epoxidation in an aqueous biphasic medium
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Chiral cross-linked polyethylenimines were used to intercalate MnIII salen catalysts, thereby inducing a chiral environment upon an achiral metal complex. The synzyme, dispersed in water, catalyzes the aqueous biphasic asymmetric epoxidation of styrene de
- Levi, Noam,Neumann, Ronny
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- Asymmetric Epoxidation of Unfunctionalized Olefins Using Novel Chiral Dihydroisoquinolinium Salts as Organocatalysts
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Abstract: Two new non-racemic chiral dihydroisoquinolinium salts with N-substituents bulkier than a methyl group have been synthesized from (1S,2R)-norephedrine. These salts were used to catalyze asymmetric epoxidation of a series of prochiral olefins. One of the two new catalysts provided higher enantioselectivities (up to 66% ee) than the reference salt containing an N-methyl substituent.
- Ali, K. Ben
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p. 638 - 646
(2021/06/02)
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- Concurrent Formation of N-H Imines and Carbonyl Compounds by Ruthenium-Catalyzed C-C Bond Cleavage of β-Hydroxy Azides
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A commercial cyclopentadienylrutenium dicarbonyl dimer ([CpRu(CO)2]2) efficiently catalyzes the formation of N-H imines and carbonyl compounds simultaneously from β-hydroxy azides via C-C bond cleavage under visible light. Density functional theory calculations for the cleavage reaction support the mechanism involving chelation of alkoxy azide species and liberation of nitrogen as the driving force. The synthetic utility of the reaction was demonstrated by a new amine synthesis promoted by chemoselective allylation of imine and synthesis of isoquinoline.
- Lee, Jeong Min,Bae, Dae Young,Park, Jin Yong,Jo, Hwi Yul,Lee, Eunsung,Rhee, Young Ho,Park, Jaiwook
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supporting information
p. 4608 - 4613
(2020/06/05)
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- Mild Iridium-Catalysed Isomerization of Epoxides. Computational Insights and Application to the Synthesis of β-Alkyl Amines
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The isomerization of epoxides to aldehydes using the readily available Crabtree's reagent is described. The aldehydes were transformed into synthetically useful amines by a one-pot reductive amination using pyrrolidine as imine-formation catalyst. The reactions worked with low catalyst loadings in very mild conditions. The procedure is operationally simple and tolerates a wide range of functional groups. A DFT study of its mechanism is presented showing that the isomerization takes place via an iridium hydride mechanism with a low energy barrier, in agreement with the mild reaction conditions. (Figure presented.).
- Cabré, Albert,Cabezas-Giménez, Juanjo,Sciortino, Giuseppe,Ujaque, Gregori,Verdaguer, Xavier,Lledós, Agustí,Riera, Antoni
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supporting information
p. 3624 - 3631
(2019/07/10)
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- Highly selective and efficient olefin epoxidation with pure inorganic-ligand supported iron catalysts
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Over the past two decades, there have been major developments in the transition iron-catalyzed selective oxidation of alkenes to epoxides; a common structure found in drug, isolated natural products, and fine chemicals. Many of these approaches have enabled highly efficient and selective epoxidation of alkenes via the design of specialized ligands, which facilitates to control the activity and selectivity of the reactions catalyzed by iron atom. Herein, we report the development of the olefin epoxidation with inorganic-ligand supported iron-catalysts using 30% H2O2 as an oxidant, and the mechanism is similar to iron-porphyrin type. With the catalyst 1, (NH4)3[FeMo6O18(OH)6], various aromatic and aliphatic alkenes were successfully transformed into the corresponding epoxides with excellent yields as well as chemo- and stereo-selectivity. This catalytic system possesses the advantages of being able to avoid the use of expensive, toxic, air/moisture sensitive and commercially unavailable organic ligands. The generality of this methodology is simple to operate and exhibits high catalytic activity as well as excellent stability, which gives it the potential to be used on an industrial scale, and maybe opens a way for the catalytic oxidation reaction via inorganic-ligand coordinated iron catalysis.
- Zhou, Zhuohong,Dai, Guoyong,Ru, Shi,Yu, Han,Wei, Yongge
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supporting information
p. 14201 - 14205
(2019/10/02)
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- Controlling Selectivity in Alkene Oxidation: Anion Driven Epoxidation or Dihydroxylation Catalysed by [Iron(III)(Pyridine-Containing Ligand)] Complexes
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A highly reactive and selective catalytic system comprising Fe(III) and macrocyclic pyridine-containing ligands (Pc-L) for alkene oxidation by using hydrogen peroxide is reported herein. Four new stable iron(III) complexes have been isolated and characterized. Importantly, depending on the anion of the iron(III) metal complex employed as catalyst, a completely reversed selectivity was observed. When X=OTf, a selective dihydroxylation reaction took place. On the other hand, employing X=Cl resulted in the epoxide as the major product. The reaction proved to be quite general, tolerating aromatic and aliphatic alkenes as well as internal or terminal double bonds and both epoxides and diol products were obtained in good yields with good to excellent selectivities (up to 93 % isolated yield and d.r.=99 : 1). The catalytic system proved its robustness by performing several catalytic cycles, without observing catalyst deactivation. The use of acetone as a solvent and hydrogen peroxide as terminal oxidant renders this catalytic system appealing.
- Tseberlidis, Giorgio,Demonti, Luca,Pirovano, Valentina,Scavini, Marco,Cappelli, Serena,Rizzato, Silvia,Vicente, Rubén,Caselli, Alessandro
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p. 4907 - 4915
(2019/08/30)
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- CERAMIDE GALACTOSYLTRANSFERASE INHIBITORS FOR THE TREATMENT OF DISEASE
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Described herein are compounds, methods of making such compounds, pharmaceutical compositions and medicaments containing such compounds, and methods of using such compounds to treat or prevent diseases or disorders associated with the enzyme ceramide galactosyltransferase (CGT), such as, for example, lysosomal storage diseases. Examples of lysosomal storage diseases include, for example, Krabbe disease and Metachromatic Leukodystrophy.
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Paragraph 000578; 000579; 000708; 000709
(2018/01/17)
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- Convenient and mild epoxidation of alkenes using heterogeneous cobalt oxide catalysts
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A general epoxidation of aromatic and aliphatic olefins has been developed under mild conditions using heterogeneous CoxOy-N/C (x=1,3; y=1,4) catalysts and tert-butyl hydroperoxide as the terminal oxidant. Various stilbenes and aliph
- Banerjee, Debasis,Jagadeesh, Rajenahally V.,Junge, Kathrin,Pohl, Marga-Martina,Radnik, Joerg,Brueckner, Angelika,Beller, Matthias
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p. 4359 - 4363
(2014/05/06)
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- Iron-catalyzed epoxidation of olefins using hydrogen peroxide
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A practical method of olefin epoxidation was developed by combining FeCl3·6H2O and 1-methylimidazole in acetone using H2O2 as the terminal oxidant. This system showed very good reactivity toward epoxidation of both terminal and substituted alkenes. The use of tridentate and tetradentate amine-bis(phenolate) ligands as additives was also examined. Modest improvement in selectivity was achieved if a bulky tridentate ligand was used. Generally, however, the simple catalyst system involving ferric chloride, 1-methylimidazole and dilute H2O 2 in acetone proved most successful in achieving good to excellent yields of epoxide products for a number of substrates, including aromatic and aliphatic alkenes.
- Hasan, Kamrul,Brown, Nicole,Kozak, Christopher M.
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experimental part
p. 1230 - 1237
(2011/06/27)
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- Bis(pyridylimino)isoindolato-iridium complexes as epoxidation catalysts for alkenes
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The reaction of the sodium salts of ligands 1a,b (1a = 1,3-bis(2-(5-(3,5- xylyl)pyridyl)imino)-5,6-dimethylisoindole, 1b = 1,3-bis(2-(4-tert-butylpyridyl) imino)-5,6-dimethylisoindole) with [Ir(μ-Cl)(COD)]2 (COD = cyclooctadiene) and [Ir(μ-Cl)(C2H4)2] 2 afforded the corresponding isoindolato complexes [{BPI(1a,b)}IrI(COD)] (2a,b) and [{BPI(1a,b)}IrI(C 2H4)2] (3a,b), respectively. The catalytic activity of the complexes 2a,b was tested in the epoxidation of a wide range of non-electron-rich olefins, using PPO (PPO = 3-phenyl-2-(phenylsulfonyl)-1,2- oxaziridine) as oxidizing agent, giving the corresponding epoxides in moderate to high yields.
- Camerano, Jose A.,Saemann, Christoph,Wadepohl, Hubert,Gade, Lutz H.
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scheme or table
p. 379 - 382
(2011/03/21)
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- Highly enantioselective biphasic iminium-catalyzed epoxidation of alkenes. on the importance of the counterion and of N(sp2)-C(sp3) Rotamers
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Diastereomeric biaryliminium cations made of an (Ra)-5,5′,6,6′, 7,7′,8,8′-octahydrobinaphthyl core and exocyclic appendages derived from (S)or (R)-3,3-dimethylbutan-2-amine are effective asymmetric epoxidation catalysts for unfunctionalized alkenes. Herei
- Novikov, Roman,Bernardinelli, Gerald,Lacour, Jerome
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experimental part
p. 596 - 606
(2009/12/01)
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- An improved iron-catalyzed epoxidation of aromatic and aliphatic olefins with hydrogen peroxide as oxidant
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A convenient and practical method for the iron-catalyzed epoxidation of aromatic and aliphatic olefins is described. The iron catalyst system is generated in situ from iron trichloride hexahydrate, pyridine-2,6-dicarboxylic acid (H2pydic), and benzylamines. By variation of the benzylamine ligand, a variety of aliphatic and aromatic olefins were oxidized in high yield (up to 96%) and good-to-excellent selectivity in the presence of hydrogen peroxide as the terminal oxidant. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.
- Bitterlich, Bianca,Schroeder, Kristin,Tse, Man Kin,Beller, Matthias
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body text
p. 4867 - 4870
(2009/05/26)
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- Novel biomimetic iron-catalysts for environmentally benign epoxidations of olefins
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A new selective and easily manageable epoxidation method is presented using an inexpensive and efficient FeCl3·6H2O and imidazole derivatives as catalysts. Aqueous hydrogen peroxide as an environmentally benign oxidant is utilized. This novel Fe/imidazole system gives moderate to excellent yields toward aromatic mono-, di-, and tri-substituted olefins.
- Schr?der, Kristin,Tong, Xiaofeng,Bitterlich, Bianca,Tse, Man Kin,Gelalcha, Feyissa Gadissa,Brückner, Angelika,Beller, Matthias
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p. 6339 - 6342
(2008/02/10)
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- New chiral iminium salt catalysts for asymmetric epoxidation
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A range of enantiomerically pure 4-substituted 5-amino-1,3-dioxanes has been condensed with 2-(2-bromoethyl)benzaldehyde to produce chiral dihydroisoquinolinium salts, which are effective asymmetric catalysts for the epoxidation of simple alkenes, giving ees of up to 71 %. Wiley-VCH Verlag GmbH & Co. KGaA, 2006.
- Bulman Page, Philip C.,Buckley, Benjamin R.,Rassias, Gerasimos A.,Blacker, A. John
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p. 803 - 813
(2007/10/03)
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- Synthetic, spectral and catalytic activity studies of ruthenium bipyridine and terpyridine complexes: Implications in the mechanism of the ruthenium(pyridine-2,6-bisoxazoline)(pyridine-2,6-dicarboxylate)-catalyzed asymmetric epoxidation of olefins utilizing H2O2
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Various Ru(L1)(L2) (1) complexes (L1 = 2,2′-bipyridines, 2,2′:6′,2″-terpyridines, 6-(4S)-4-phenyl-4,5-dihydro-oxazol-2-yl-2,2′-bipyridinyl or 2,2′-bipyridinyl-6-carboxylate; L2 = pyridine-2,6-dicarboxylate, pyridine-2-carboxylate or 2,2′-bipyridinyl-6-carboxylate) have been synthesized (or in situ generated) and tested on epoxidation of olefins utilizing 30% aqueous H2O2. The complexes containing pyridine-2,6-dicarboxylate show extraordinarily high catalytic activity. Based on the stereoselective performance of chiral ruthenium complexes containing non-racemic 2,2′-bipyridines including 6-[(4S)-4-phenyl-4,5-dihydro-oxazol-2-yl]-[2,2′]bipyridinyl new insights on the reaction intermediates and reaction pathway of the ruthenium-catalyzed enantioselective epoxidation are proposed. In addition, a simplified protocol for epoxidation of olefins using urea hydrogen peroxide complex as oxidizing agent has been developed.
- Tse, Man Kin,Jiao, Haijun,Anilkumar, Gopinathan,Bitterlich, Bianca,Gelalcha, Feyissa Gadissa,Beller, Matthias
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p. 4419 - 4433
(2007/10/03)
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- Process for the ruthenium-catalysed epoxidation of olefins by means of hydrogen peroxide
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The present invention relates to a process for the epoxidation of olefins using catalysts based on ruthenium complexes in the presence of hydrogen peroxide.
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Page/Page column 5-6
(2008/06/13)
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- A simple method for epoxidation of olefins using sodium chlorite as an oxidant without a catalyst
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Sodium chlorite has been demonstrated to be capable of epoxidizing a variety of olefins at 55-65 °C (oil bath). Chlorine dioxide is believed to be the pivotal epoxidizing agent in the reaction on the basis of the mechanistic studies.
- Geng, Xue-Li,Wang, Zhi,Li, Xiao-Qiang,Zhang, Chi
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p. 9610 - 9613
(2007/10/03)
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- Convenient method for epoxidation of alkenes using aqueous hydrogen peroxide
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(Chemical Equation Presented) The complex [Ru(tpy)(pydic)] (1a) is an active catalyst for epoxidation of alkenes by aqueous 30% hydrogen peroxide in tertiary alcohols. The protocol is simple to operate and gives the corresponding epoxides in good to excellent yields. Chiral enantiopure [Ru(tpy*)(pydic) ] complexes have been synthesized and successfully applied in this procedure.
- Man, Kin Tse,Klawonn, Markus,Bhor, Santosh,Doebler, Christian,Anilkumar, Gopinathan,Hugl, Herbert,Maegerlein, Wolfgang,Beller, Matthias
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p. 987 - 990
(2007/10/03)
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- Process for the asymmetric epoxidation of olefins
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The present invention relates to a catalyst based on ruthenium complexes and to a process for the asymmetric epoxidation of olefins using catalysts based on ruthenium complexes.
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Page/Page column 5
(2008/06/13)
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- Asymmetric aminolysis of aromatic epoxides: A facile catalytic enantioselective synthesis of anti-β-amino alcohols
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The first asymmetric aminolysis of trans-aromatic epoxides with anilines is described. The process affords enantioenriched anti-β-amino alcohols in up to 99% ee. The complete regio- and diastereoselectivity observed uses commercially available [Cr(Salen)CI] as a Lewis acid catalyst and in combination with a very simple experimental procedure renders the present reaction a facile and practical tool for the synthesis of chiral nonracemic anti-β-amino alcohols.
- Bartoli, Giuseppe,Bosco, Marcella,Carlone, Armando,Locatelli, Manuela,Massaccesi, Massimo,Melchiorre, Paolo,Sambri, Letizia
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p. 2173 - 2176
(2007/10/03)
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- Lithiation and reactions of stilbene oxides: Synthetic utility
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(Chemical Equation Presented) The lithiation of trans- and cis-stilbene oxides (±)-1 and 8 has been investigated. While with 8, lithiation occurred exclusively at the benzylic position, with the trans isomer (±)-1, ortho-lithiation competed with α-lithiation depending upon the experimental conditions. The configurational stability of the α-lithiated cis- and trans-stilbene oxides (±)-2 and (±)-9, respectively, was proved as well as that of scalemic stilbene oxide (R,R)-2.
- Florio, Saverio,Aggarwal, Varinder,Salomone, Antonio
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p. 4191 - 4194
(2007/10/03)
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- Epoxide Formation by Indirect Electroreductive Coupling between Aldehydes or Ketones and Activated gem-Dichloro Compounds
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Epoxides are prepared by indirect electroreductive coupling of carbonyl compounds (aldehydes or ketones) and activated gem-dichloro compounds. This process is more efficient with aryl ketones than with aryl aldehydes. Though yields are only moderate, this
- Oudeyer,Leonel,Paugam,Nedelec
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p. 389 - 400
(2007/10/03)
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- A new protocol for the in situ generation of aromatic, heteroaromatic, and unsaturated diazo compounds and its application in catalytic and asymmetric epoxidation of carbonyl compounds. Extensive studies to map out scope and limitations, and rationalization of diastereo- and enantioselectivities
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A variety of metalated tosylhydrazone salts derived from benzaldehyde have been prepared and were reacted with benzaldehyde in the presence of tetrahydrothiophene (THT) (20 mol %) and Rh2(OAc)4 (1 mol %) to give stilbene oxide. Of the lithium, sodium, and potassium salts tested, the sodium salt was found to give the highest yield and selectivity. This study was extended to a wide variety of aromatic, heteroaromatic, aliphatic, α,β-unsaturated, and acetylenic aldehydes and to ketones. On the whole, high yields of epoxides with moderate to very high diastereoselectivities were observed. A broad range of tosylhydrazone salts derived from aromatic, heteroaromatic, and α,β-unsaturated rated aldehydes was also examined using the same protocol in reactions with benzaldehyde, and again, good yields and high diastereoselectivities were observed in most cases. Thus, a general process for the in situ generation of diazo compounds from tosylhydrazone sodium salts has been established and applied in sulfur-ylide mediated epoxidation reactions. The chiral, camphor-derived, [2.2.1] bicyclic sulfide 7 was employed (at 5-20 mol % loading) to render the above processes asymmetric with a range of carbonyl compounds and tosylhydrazone sodium salts. Benzaldehyde tosylhydrazone sodium salt gave enantioselectivities of 91 ± 3% ee and high levels of diastereoselectivity with a range of aldehydes. However, tosylhydrazone salts derived from a range of carbonyl compounds gave more variable selectivities. Although those salts derived from electron-rich or neutral aldehydes gave high enantioselectivities, those derived from electron-deficient or hindered aromatic aldehydes gave somewhat reduced enantioselectivities. Using α,β-unsaturated hydrazones, chiral sulfide 7 gave epoxides with high diastereoselectivities, but only moderate yields were achieved (12-56%) with varying degrees of enantioselectivity. A study of solvent effects showed that, while the impact on enantioselectivity was small, the efficiency of diazo compound generation was influenced, and CH3CN and 1,4-dioxane emerged as the optimum solvents. A general rationalization of the factors that influence both relative and absolute stereochemistry for all of the different substrates is provided. Reversibility in formation of the betaine intermediate is an important issue in the control of diastereoselectivity. Hence, where low diastereocontrol was observed, the results have been rationalized in terms of the factors that contribute to the reduced reversion of the syn betaine back to the original starting materials. The enantioselectivity is governed by ylide conformation, facial selectivity in the ylide reaction, and, again, the degree of reversibility in betaine formation. From experimental evidence and calculations, it has been shown that sulfide 7 gives almost complete control of facial selectivity, and, hence, it is the ylide conformation and degree of reversibility that are responsible for the enantioselectivity observed. A simple test has been developed to ascertain whether the reduced enantioselectivity observed in particular cases is due to poor control in ylide conformation or due to partial reversibility in the formation of the betaine.
- Aggarwal, Varinder K.,Alonso, Emma,Bae, Imhyuck,Hynd, George,Lydon, Kevin M.,Palmer, Matthew J.,Patel, Mamta,Porcelloni, Marina,Richardson, Jeffery,Stenson, Rachel A.,Studley, John R.,Vasse, Jean-Luc,Winn, Caroline L.
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p. 10926 - 10940
(2007/10/03)
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- Process for the preparation of an oxirane, aziridine or cyclopropane
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A process for the preparation of an oxirane, aziridine or cyclopropane of formula (I), wherein X is oxygen, NR4or CHR5; R1is hydrogen, alkyl, aryl, heteroaromatic, heterocyclic or cycloalkyl; R2is hydrogen, alkyl, aryl, heteroaromatic, CO2R8, CHR14NHR13, heterocyclic or cycloalkyl; or R1and R2join together to form a cycloalkyl ring; R3and R10are, independently, hydrogen, alkyl, aryl, heteroaromatic, CO2R8, R83Sn, CONR8R9, trialkylsilyl or triarylsilyl; R4is an electron withdrawing group; R5is alkyl, cycloalkyl, aryl, heteroaromatic, SO2R8, SO3R8, COR8, CO2R8, CONR8R9, PO(R8)2, PO(OR8)2or CN; R8and R9are independently alkyl or aryl; and R13and R14are independently hydrogen, alkyl or aryl is provided. The process comprises degrading a compound of formula (II), (IIa), (IIb) or (IIc): wherein R3and R10are as defined above; Y is a cation; depending on the nature of Y, r is 1 or 2; and L is a suitable leaving group, to form a diazo compound. The diazo compound is reacted with a suitable transition metal catalyst, and the product thereof reacted with a sulphide of formula SR6R7, wherein R6and R7are independently alkyl, aryl or heteroaromatic, or R6and R7join together to form an optionally substituted ring which optionally includes an additional heteroatom. This product is then reacted with an aldehyde, ketone, imine or alkene.
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- Catalytic asymmetric synthesis of epoxides from aldehydes using sulfur ylides with in situ generation of diazocompounds
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A practical, general, and convergent to epoxides with control of the relative and absolute stereochemistry has been achieved by generating the reactive intermediate (the diazo compound) in situ from tosylhydrazone salts (see scheme, PTC = phase-transfer catalyst, Ts = toluene-4-sulfonyl). High yields (58-82%), high d.r. (88:12-98:2), and high ee values (87-94%) have been obtained using a new class of stable chiral sulfides at low catalyst loading (5 mol%) and [Rh2(OAc)4] (0.5 mol%).
- Aggarwal, Varinder K.,Alonso, Emma,Hynd, George,Lydon, Kevin M.,Palmer, Matthew J.,Porcelloni, Marina,Studley, John R.
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p. 1430 - 1433
(2007/10/03)
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- A novel epoxidation reaction of olefins using a combination of chloramine-M, benzaldehyde, and benzyltriethylammonium chloride
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A combination of Chloramine-M (CH3SO2NClNa), benzaldehyde, and benzyltriethylammonium chloride (BTEAC) was found to epoxidize a wide range of olefins. While epoxidation of trans-olefins provided exclusively trans- epoxides, cis-olefins (cis-stilbene, cis-β-methylstyrene, and 4-cis-octene) gave trans-epoxides as major products. Good to excellent diastereoselectivities were obtained for epoxidation of two substituted cyclohexenes. Chloramine-T was found to give a slower reaction than Chloramine-M. cis-N-Sulfonyloxaziridine D is proposed to be the epoxidizing agent in this novel epoxidation reaction on the basis of the mechanistic studies.
- Yang, Dan,Zhang, Chi,Wang, Xue-Chao
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p. 4039 - 4043
(2007/10/03)
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- Thermolysis of substituted tert-butyl-(2-phenyl-prop-2-yl) peroxides
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tert-Butyl-(2-phenyl-1-methoxy-prop-2-yl)-peroxide (1a), tert-butyl-(2-phenyl-1-acetoxy-prop-2-yl)-peroxide (1b) and tert-butyl-(1,2-diphenyl-prop-2-yl)-peroxide (1c) were prepared from t-BuOOH and 1-methoxy-2-phenyl-prop-2-ol (a), 2-phenyl-2-methyl-oxirane (b) and, respectively, 1,2-diphenyl-propan-2-ol (c). The peroxides 1a-c were characterized by NMR spectroscopy and elemental analysis. Kinetic data were determined and the products analyzed from thermolysis of 1a-c at 110-155°C in cumene as the solvent. The major thermolysis product from 1a-c was acetophenone, formed via fragmentation of intermediate alkoxy radicals: R-CH2-C(Ph)(Me)O (R: MeO (a); AcO (b); Ph (c)). Wiley-VCH Verlag GmbH, 1999.
- Suprun
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p. 363 - 368
(2007/10/03)
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- A Novel Catalytic Cycle for the Synthesis of Epoxides Using Sulfur Ylides
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A novel, neutral catalytic cycle for the synthesis of epoxides from carbonyl compounds and diazo compounds using catalytic quantities of transition metal salts and sulfides has been developed.In this catalytic cycle, the diazo compounds is decomposed by the transition metal salt to give a metallocarbene, and this is picked up to the sulfide to give a sulfur ylide, which then reacts with the aldehyde to give an epoxide and returns the sulfide back into the catalytic cycle.To obtain good yields of epoxides it is necessary to maintain a low concentration of the diazo compound (by slow addition), otherwise dimerisation of the diazo compound is the dominant reaction.Factors affecting the outcome of the reaction were studied.The reactions are relatively insensitive to solvent, but are sensitive to the structure of the sulfide, the metal salt and the concentration.Unhindered sulfides give good yields of epoxides with any metal salt, but with hindered sufides higher yields are obtained with Cu(acac)2 than with Rh2(OAc)4.The yields of epoxides are sensitive to sulfide concentration especially when using substoichiometric amounts of sulfides.Higher concentration leads to faster rates of formation and subsequent reaction of the sulfur ylides, and consequently to higher yields.This novel catalytic cycle has also been applied to base-sensitive aldehydes.We found that our new catalytic cycle for epoxidation gives much improved yields of epoxides compared to those obtained by traditional sulfur ylide chemistry and is tolerant to a wide variety of sensitive functional groups.Ketones also participate in the catalytic cycle, although they give reduced yields of epoxides compared to aldehydes and require a slightly elevated temperature. - Keywords: catalysis; diazo compounds; epoxidations; sulfur ylides; synthetic methods
- Aggarwal, Varinder K.,Abdel-Rahman, Hesham,Fan, Li,Jones, Ray V. H.,Standen, Mike C. H.
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p. 1024 - 1030
(2007/10/03)
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- Oxidative photofragmentation of α,β-amino alcohols via single electron transfer: Cooperative reactivity of donor and acceptor ion radicals in photogenerated contact radical ion pairs
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The studies presented in this paper show that α,β-amino alcohols undergo a very clean C-C bond cleavage upon SET (single electron transfer) oxidation by photoexcited electron acceptors in a process which generally culminates in two-electron reduction of the acceptors. For a number of different α,β-amino alcohols, the oxidative fragmentation occurs in a high chemical yield (>90%), yet with low to medium quantum efficiencies (0.0001-0.1) which vary strongly depending on the properties of electron donor (D), acceptor (A), and solvent. The net quantum efficiency reflects the competition between back electron transfer and the chemical redox process. Detailed mechanistic studies were carried out to investigate the visible light induced oxidative fragmentation of α,β-amino alcohols in the presence of electron acceptors including, thioindigo (TI), 9,10-dicyanoanthracene (DCA), 2,6,9,10-tetracyanoanthracene (TCA), and 1,4-dicyanonaphthalene (DCN). Cosensitized (biphenyl) photoredox leads to free ions, A- and D+, and moderately efficient unassisted fragmentation of D+. Quenching of 1A* by electron donor (D) to give a solvent separated radical ion pair (SSRIP) leads to a very inefficient reaction. In contrast, quenching to give a contact radical ion pair (CRIP) gives a relatively efficient reaction. This reaction is sensitive to the stereochemistry of the amino alcohol, suggesting a preferred anticoplanar configuration during the C-C bond cleavage process. The critical matching of reactivity of acceptor and donor ion radicals allows a rapid reaction to occur in the relatively narrow time window between formation and decay of the contact radical ion pair.
- Ci, Xiaohong,Kellett, Matthew A.,Whitten, David G.
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p. 3893 - 3903
(2007/10/02)
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- THE PHOTOCHEMICAL PREPARATION OF OZONIDES BY ELECTRON-TRANSFER PHOTO-OXYGENATION OF EPOXIDES
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9,10-Dicyanoanthracene (DCA) sensitizes the electron-transfer photo-oxygenation of epoxides in oxygen-saturated acetonitrile to form ozonides.Epoxides with oxidation potentials lower than 2 V vs SCE quench the fluorescence of DCA and are converted to the
- Schaap, A. Paul,Siddiqui, Shahabuddin,Prasad, Girija,Palomino, Eduardo,Sandison, Mark
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p. 2229 - 2236
(2007/10/02)
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