- The design of novel N-4′-pyridinyl-α-methyl proline derivatives as potent catalysts for the kinetic resolution of alcohols
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A novel family of chiral acylation catalysts based on a N-4′-pyridinyl-α-methyl proline structure has been studied. A set of 31 compounds has been easily prepared and screened in the kinetic resolution of racemic alcohol 33 resulting in high enantioselectivities in most cases. From results obtained, H-bonding interactions between the catalyst and the substrate would appear essential to afford high enantioselectivity during the catalytic acylation. Additional solvent dependence and anhydride studies have been made to better identify the mechanism. This work has been further extended to the study of a number of structurally different alcohols. Ethanolamine derivatives in particular were found to be highly effective substrates (up to S = 18.8) in the kinetic resolution.
- Priem, Ghislaine,Pelotier, Béatrice,Macdonald, Simon J. F.,Anson, Mike S.,Campbell, Ian B.
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Read Online
- Diastereoselective reduction of alkenylboronic esters as a new method for controlling the stereochemistry of up to three adjacent centers in cyclic and acyclic molecules
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(figure presented) cis-Boronates are readily available via a diastereoselective Pd-catalyzed reduction of tetrasubstituted alkenylboronic esters using H2. Applying the reaction conditions presented to unsaturated open-chain boronic esters allows the stereochemistry of up to three adjacent centers to be controlled.
- Hupe, Eike,Marek, Ilan,Knochel, Paul
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Read Online
- PNO ligand containing planar chiral ferrocene and axial chiral diphenol and application thereof
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The invention discloses a PNO ligand containing planar chiral ferrocene and axially chiral diphenol and application of the PNO ligand. The PNO ligand containing planar chiral ferrocene and axially chiral diphenol is shown in any one of general formulas (I)-(IV). Or a PNO ligand containing planar chiral ferrocene and axial chiral diphenol as shown in any one of general formulas (V)-(VIII); compared with a previously reported tridentate ligand, the PNO ligand containing the planar chiral ferrocene and the axial chiral diphenol not only has good stability and easiness in synthesis, but also has planar chirality and axial chirality and has a good chiral environment, so that not only is excellent selectivity to a substrate ensured, but also the catalytic activity of a catalyst and the application range of the substrate are further improved. The chiral raw materials used in the invention are commercial bulk products, and the ligand synthesis route is simpler, so that large-scale production can be well carried out, and the method has a huge commercial application prospect.
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Paragraph 0098-0099
(2021/06/23)
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- ARYLCYCLOHEXYLAMINE DERIVATIVES AND THEIR USE IN THE TREATMENT OF PSYCHIATRIC DISORDERS
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Provided herein are arylcyclohexylamine derivatives and their use in the treatment of psychiatric disorders.
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Paragraph 0327
(2021/07/02)
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- Method for preparing alcohol through reaction of Suzuki no exogenous alkali (by machine translation)
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The method for synthesizing the alcohol compound by. using the method disclosed by the invention for preparing .the alcohol compound by adopting the method Suzuki disclosed by the invention has the advantages that the reaction system, is convenient and convenient, to prepare, and the reaction system is convenient to prepare . Suzuki. (by machine translation)
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Paragraph 0022-0026
(2020/02/14)
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- Erbium-Catalyzed Regioselective Isomerization-Cobalt-Catalyzed Transfer Hydrogenation Sequence for the Synthesis of Anti-Markovnikov Alcohols from Epoxides under Mild Conditions
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Herein, we report an efficient isomerization-transfer hydrogenation reaction sequence based on a cobalt pincer catalyst (1 mol %), which allows the synthesis of a series of anti-Markovnikov alcohols from terminal and internal epoxides under mild reaction conditions (≤55 °C, 8 h) at low catalyst loading. The reaction proceeds by Lewis acid (3 mol % Er(OTf)3)-catalyzed epoxide isomerization and subsequent cobalt-catalyzed transfer hydrogenation using ammonia borane as the hydrogen source. The general applicability of this methodology is highlighted by the synthesis of 43 alcohols from epoxides. A variety of terminal (23 examples) and 1,2-disubstituted internal epoxides (14 examples) bearing different functional groups are converted to the desired anti-Markovnikov alcohols in excellent selectivity and yields of up to 98%. For selected examples, it is shown that the reaction can be performed on a preparative scale up to 50 mmol. Notably, the isomerization step proceeds via the most stable carbocation. Thus, the regiochemistry is controlled by stereoelectronic effects. As a result, in some cases, rearrangement of the carbon framework is observed when tri-and tetra-substituted epoxides (6 examples) are converted. A variety of functional groups are tolerated under the reaction conditions even though aldehydes and ketones are also reduced to the respective alcohols under the reaction conditions. Mechanistic studies and control experiments were used to investigate the role of the Lewis acid in the reaction. Besides acting as the catalyst for the epoxide isomerization, the Lewis acid was found to facilitate the dehydrogenation of the hydrogen donor, which enhances the rate of the transfer hydrogenation step. These experiments additionally indicate the direct transfer of hydrogen from the amine borane in the reduction step.
- Liu, Xin,Longwitz, Lars,Spiegelberg, Brian,T?njes, Jan,Beweries, Torsten,Werner, Thomas
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p. 13659 - 13667
(2020/11/30)
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- A Practical and Stereoselective In Situ NHC-Cobalt Catalytic System for Hydrogenation of Ketones and Aldehydes
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Homogeneous catalytic hydrogenation of carbonyl groups is a synthetically useful and widely applied organic transformation. Sustainable chemistry goals require replacing conventional noble transition metal catalysts for hydrogenation by earth-abundant base metals. Herein, we report how a practical in situ catalytic system generated by easily available pincer NHC precursors, CoCl2, and a base enabled efficient and high-yielding hydrogenation of a broad range of ketones and aldehydes (over 50 examples and a maximum turnover number [TON] of 2,610). This is the first example of NHC-Co-catalyzed hydrogenation of C=O bonds using flexible pincer NHC ligands consisting of a N-H substructure. Diastereodivergent hydrogenation of substituted cyclohexanone derivatives was also realized by fine-tuning of the steric bulk of pincer NHC ligands. Additionally, a bis(NHCs)-Co complex was successfully isolated and fully characterized, and it exhibits excellent catalytic activity that equals that of the in-situ-formed catalytic system. Catalytic hydrogenation is a powerful tool for the reduction of organic compounds in both fine and bulk chemical industries. To improve sustainability, more ecofriendly, inexpensive, and earth-abundant base metals should be employed to replace the precious metals that currently dominate the development of hydrogenation catalysts. However, the majority of the base-metal catalysts that have been reported involve expensive, complex, and often air- and moisture-sensitive phosphine ligands, impeding their widespread application. From a mixture of the stable CoCl2, imidazole salts, and a base, our newly developed catalytic system that formed easily in situ enables efficient and stereoselective hydrogenation of C=O bonds. We anticipate that this easily accessible catalytic system will create opportunities for the design of practical base-metal hydrogenation catalysts. A practical in situ catalytic system generated by a mixture of easily available pincer NHC precursors, CoCl2, and a base enabled highly efficient hydrogenation of a broad range of ketones and aldehydes (over 50 examples and up to a turnover number [TON] of 2,610). Diastereodivergent hydrogenation of substituted cyclohexanone derivatives was also realized in high selectivities. Moreover, the preparation of a well-defined bis(NHCs)-Co complex via this pincer NHC ligand consisting of a N-H substructure was successful, and it exhibits equally excellent catalytic activity for the hydrogenation of C=O bonds.
- Zhong, Rui,Wei, Zeyuan,Zhang, Wei,Liu, Shun,Liu, Qiang
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supporting information
p. 1552 - 1566
(2019/06/14)
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- (Poly)cationic λ3-Iodane-Mediated Oxidative Ring Expansion of Secondary Alcohols
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Herein, a simplified approach to the synthesis of medium-ring ethers through the electrophilic activation of secondary alcohols with (poly)cationic λ3-iodanes (N-HVIs) is reported. Excellent levels of selectivity are achieved for C–O bond migration over established α-elimination pathways, enabled by the unique reactivity of a novel 2-OMe-pyridine-ligated N-HVI. The resulting hexafluoroisopropanol (HFIP) acetals are readily derivatized with a range of nucleophiles, providing a versatile functional handle for subsequent manipulations. The utility of this methodology for late-stage natural product derivatization was also demonstrated, providing a new tool for diversity-oriented synthesis and complexity-to-diversity (CTD) efforts. Preliminary mechanistic investigations reveal a strong effect of alcohol conformation on the reactive pathway, thus providing a predictive power in the application of this approach to complex molecule synthesis.
- Walters, Jennifer C.,Tierno, Anthony F.,Dubin, Aimee H.,Wengryniuk, Sarah E.
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supporting information
p. 1460 - 1464
(2018/04/06)
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- Directed β C-H Amination of Alcohols via Radical Relay Chaperones
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A radical-mediated strategy for β C-H amination of alcohols has been developed. This approach employs a radical relay chaperone, which serves as a traceless director that facilitates selective C-H functionalization via 1,5-hydrogen atom transfer (HAT) and enables net incorporation of ammonia at the β carbon of alcohols. The chaperones presented herein enable direct access to imidate radicals, allowing their first use for H atom abstraction. A streamlined protocol enables rapid conversion of alcohols to their β-amino analogs (via in situ conversion of alcohols to imidates, directed C-H amination, and hydrolysis to NH2). Mechanistic experiments indicate HAT is rate-limiting, whereas intramolecular amination is product- and stereo-determining.
- Wappes, Ethan A.,Nakafuku, Kohki M.,Nagib, David A.
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supporting information
p. 10204 - 10207
(2017/08/10)
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- Diastereoselective and enantioselective alkaline-hydrolysis of 2-aryl-1-cyclohexyl acetate: a CAL-B catalyzed deacylation/acylation tandem process
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Candida antarctica lipase proved to be a particularly efficient lipase for the resolution of racemic 2-arylcyclohexyl acetate in hydrolysis reaction with Na2CO3 in an organic medium. The (1R,2S)-trans-2-arylcyclohexanols 2a–2d were obtained with high ee values (up to >99%) and the selectivity reached E > 200. The influence of the enol ester and the solvent on (±)-trans-2-arylcyclohexanol in the CAL-B catalyzed acylation was also studied and compared with the deacylation. The CAL-B exhibits a better affinity for the alkaline hydrolysis reaction compared with acylation with the enol esters in the same organic solvents. The best conditions were applied to resolve a stereoisomeric mixture cis/trans-2-phenyl-1-cyclohexanol and its corresponding acetate by acylation and deacylation. The obtained results show a highly enantio- and diastereoselectivity of the CAL-B during the acylation and the deacylation in favor of the trans-(R)-enantiomer product. The resolution of a mixture of cis/trans-2-arylcyclohexanols was an easy, convenient approach to provide only one stereoisomer of a mixture of four with high enantiomeric excess.
- Belkacemi, Fatma Zahra,Merabet-Khelassi, Mounia,Aribi-Zouioueche, Louisa,Riant, Olivier
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supporting information
p. 1644 - 1650
(2017/10/12)
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- Promising Ni/Al-SBA-15 catalysts for hydrodeoxygenation of dibenzofuran into fuel grade hydrocarbons: Synergetic effect of Ni and Al-SBA-15 support
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This work has been undertaken with the aim of designing promising noble-metal-free catalysts for efficient hydrodeoxygenation (HDO) of dibenzofuran (DBF) into fuel grade hydrocarbons. For this, various Ni/Al-SBA-15 catalysts with different Si/Al (50, 60, 70 and 80) mole ratios were synthesized and their catalytic performance was tested for HDO of DBF in a batch reactor. The catalysts were systematically characterized using XRD, N2-adsorption-desorption, Raman, H2-TPR, NH3-TPD, XRF, and FESEM techniques. The activity results showed that the HDO of DBF proceeds via hydrogenation of benzene on the Ni sites followed by cleavage of C-O bonds on the acidic sites of the catalyst to yield unsaturated hydrocarbons. Further hydrogenation of unsaturated hydrocarbons on the Ni sites gives bicyclohexane as the major product. Remarkably, a 100% DBF conversion was found for all the catalysts except for Ni/SBA-15 and Ni/Al-SBA-15(80) (Si/Al mole ratio = 80) catalysts, which showed 97.97 and 99.31%, respectively. A significant observation noticed in this study is that the incorporation of Al into Ni/SBA-15 results in an outstanding improvement in the selectivity of the bicyclohexane product. Among the catalysts tested, the Ni/Al-SBA-15(50) (Si/Al mole ratio = 50) catalyst showed the highest efficiency, with superior selectivity of ~87% for bicyclohexane and ~96% degree of deoxygenation at 10 MPa, 260 °C and 5 h. The obtained structure-activity results reveal the synergetic effect of Ni and support in HDO of DBF reaction: the concentration of acidic sites has a significant effect on the selectivity of the desired products.
- Gbadamasi, Sharafadeen,Ali, Tammar Hussein,Voon, Lee Hwei,Atta, Abdulazeez Yusuf,Sudarsanam, Putla,Bhargava, Suresh K.,Abd Hamid, Sharifah Bee
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p. 25992 - 26002
(2016/03/25)
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- Effective hydrodeoxygenation of dibenzofuran by a bimetallic catalyst in water
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Effective hydrodeoxygenation (HDO) of dibenzofuran (DBF) catalyzed by a bimetallic nickel/platinum (Ni/Pt) catalyst in water was demonstrated at 200 °C and 1.2 MPa hydrogen (H2) pressure. The bimetallic catalysts prepared by a wet chemical method exhibit prominent activity that overcomes the limitations of use of a single Ni or Pt metal catalyst. The yield of HDO products can be up to 90%. Reaction results indicate that the conversion of DBF was affected by the reaction temperature and H2 pressure. The deoxygenation selectivity was strongly dependent on reaction temperature. The reaction pathway is also proposed.
- Dong, Peng,Lu, Guo-Ping,Cai, Chun
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p. 1605 - 1609
(2016/02/19)
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- Diastereoselective and Enantioselective Silylation of 2-Arylcyclohexanols
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The silylation-based kinetic resolution of trans 2-arylcyclohexanols was accomplished by employing a triaryl silyl chloride as the derivatizing reagent with a commercially available isothiourea catalyst. The methodology is selective for the trans diastereomer over the cis, which provides an opportunity to selectively derivatize one stereoisomer out of a mixture of four. By employing this technology, a facile, convenient method to form a highly enantiomerically enriched silylated alcohol was accomplished through a one-pot reduction-silylation sequence that started with a 2-aryl-substituted ketone.
- Wang, Li,Akhani, Ravish K.,Wiskur, Sheryl L.
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supporting information
p. 2408 - 2411
(2015/05/27)
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- Nickel-catalyzed regiodivergent opening of epoxides with aryl halides: Co-catalysis controls regioselectivity
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Epoxides are versatile intermediates in organic synthesis, but have rarely been employed in cross-coupling reactions. We report that bipyridine-ligated nickel can mediate the addition of functionalized aryl halides, a vinyl halide, and a vinyl triflate to epoxides under reducing conditions. For terminal epoxides, the regioselectivity of the reaction depends upon the cocatalyst employed. Iodide cocatalysis results in opening at the less hindered position via an iodohydrin intermediate. Titanocene cocatalysis results in opening at the more hindered position, presumably via TiIII-mediated radical generation. 1,2-Disubstituted epoxides are opened under both conditions to form predominantly the trans product.
- Zhao, Yang,Weix, Daniel J.
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supporting information
p. 48 - 51
(2014/01/23)
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- Construction of a chiral quaternary carbon center by catalytic asymmetric alkylation of 2-arylcyclohexanones under phase-transfer conditions
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In this paper, we present an asymmetric alkylation of modified 2-arylcyclohexanones that employs a novel chiral ammonium bromide as a phase-transfer catalyst and an achiral auxiliary as a controller to improve the enantioselectivity to afford optically enriched products having a chiral quaternary carbon center.
- Kano, Taichi,Hayashi, Yumi,Maruoka, Keiji
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supporting information
p. 7134 - 7137
(2013/06/27)
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- Influence of chiral thiols on the diastereoselective synthesis of γ-lactams from cyclic anhydrides
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The synthesis of γ-lactams from both four-component and imine-anhydride reactions is reported. The synthesis of 2-phenylcyclohexanethiol is described and this compound was evaluated along with an additional seven chiral thiols. A range of selectivity and yields was observed and comparisons to established reactions are made in order to account for the observed reactivity.
- Younai, Ashkaan,Fettinger, James C.,Shaw, Jared T.
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scheme or table
p. 4320 - 4327
(2012/07/28)
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- A boron-based synthesis of the natural product (+)-trans- dihydrolycoricidine
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Diastereoselective diboration results in the highly selective 1,4-dihydroxylation of chiral cyclohexadienes (see scheme). Together with the catalytic enantioselective conjugate allylboration, the diene diboration facilitates the asymmetric synthesis of the cytotoxic agent (+)-trans- dihydrolycoricidine (1). pin=pinacol. Copyright
- Poe, Sarah L.,Morken, James P.
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supporting information; experimental part
p. 4189 - 4192
(2011/06/20)
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- PALLADIUM CATALYSTS
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The invention relates to a particulate substance comprising a particulate porous support coupled to a palladium species. The palladium species may comprise palladium nanoclusters. The particulate substance may be used as a catalyst for conducting a carbon-carbon coupling reaction or a reduction.
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Page/Page column 17; 19
(2010/05/13)
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- Palladium nanoclusters supported on propylurea-modified siliceous mesocellular foam for coupling and hydrogenation reactions
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This paper describes the synthesis, characterization and applications of palladium (Pd) nanoparticles supported on siliceous mesocellular foam (MCF). Pd nanoparticles of 2-3 nm and 4-6 nm were used in reactions involving molecular hydrogen (such as hydrogenation of double bonds and reductive amination), transfer hydrogenation of ketones and epoxides, and coupling reactions (such as Heck and Suzuki reactions). They successfully catalyzed all these reactions with excellent yield and selectivity. This heterogeneous catalyst was easily recovered by filtration, and recycled several times without any significant loss in activity and selectivity. The palladium leaching in the reactions was determined to be much less than the FDA-approved limit of 5 ppm. Furthermore, the catalyst can be stored and handled under normal atmospheric conditions. This immobilized catalyst allows for ease of recovery/reuse and minimization of waste generation, which are of great interest in the development of green chemical processes.
- Erathodiyil, Nandanan,Ooi, Samuel,Seayad, Abdul M.,Han, Yu,Lee, Su Seong,Ying, Jackie Y.
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experimental part
p. 3118 - 3125
(2009/04/08)
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- Discovery of N-(2-aryl-cyclohexyl) substituted spiropiperidines as a novel class of GlyT1 inhibitors
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Screening of the Roche compound library led to the identification of cis-N-(2-phenyl-cyclohexyl)-spiropiperidine 1 as structurally novel GlyT1 inhibitor. The SAR, which was developed in this series, resulted in the discovery of highly potent compounds displaying excellent selectivity against the GlyT2 isoform.
- Pinard, Emmanuel,Ceccarelli, Simona M.,Stalder, Henri,Alberati, Daniela
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p. 349 - 353
(2007/10/03)
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- Highly diastereoselective catalytic Meerwein-Ponndorf-Verley reductions
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Very practical synthesis of ephedrine analogues in high yields and enantiopurity was realized by a highly diastereoselective Meerwein-Ponndorf- Verley (MPV) reduction of protected α-amino aromatic ketones using catalytic aluminum isopropoxide. The high anti selectivity resulted from the chelation of the nitrogen anion to the aluminum. In contrast, high syn selectivity was obtained with α-alkoxy ketones and other compounds via Felkin-Ahn control.
- Yin, Jingjun,Huffman, Mark A.,Conrad, Karen M.,Armstrong III, Joseph D.
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p. 840 - 843
(2007/10/03)
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- Reduction of carbonyl compounds by lanthanide metal/2-propanol: In-situ generation of samarium isopropyloxide for stereoselective Meerwein-Ponndorf- Verley reduction
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The reduction of ketones and aldehydes with lanthanide metals (La, Ce, Sm, Yb) and a catalytic amount of iodine (5 mol %) in iPrOH proceeded smoothly to produce the corresponding alcohols as the major products in good yield, while in THF, methanol, and ethanol the pinacols were mainly produced. The yields of alcohols were improved most effectively by the use of Sm metal, the amount of pinacol produced thus being minimized. The actual reducing agent may be samarium isopropyloxide, which mediates the Meerwein-Ponndorf-Verley-type hydride-transfer reaction, since the reaction can be carried out catalytically with respect to samarium. The stereoselectivities of the reductions of the 2- and 4-substituted cyclohexanones with Sm/iPrOH were higher than those achieved with SmI2/iPrOH or Sm/ H20. The asymmetric reduction of acetophenone could be achieved to give the 1-phenylethanol in up to 95% ee in the presence of the chiral ligand 7. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.
- Fukuzawa, Shin-Ichi,Nakano, Narihito,Saitoh, Takahide
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p. 2863 - 2867
(2007/10/03)
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- Recyclable Polyurea-Microencapsulated Pd(0) Nanoparticles: An Efficient Catalyst for Hydrogenolysis of Epoxides
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(Matrix presented) Pd nanoparticles (~2 nm in size) microencapsulated in polyurea is an efficient and recyclable catalyst for reductive ring-opening hydrogenolysis of epoxides, using either HCOOH/Et3N or H2 as a hydrogen donor.
- Ley, Steven V.,Mitchell, Claire,Pears, David,Ramarao, Chandrashekar,Yu, Jin-Quan,Zhou, Wuzong
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p. 4665 - 4668
(2007/10/03)
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- Free-radical hydroxylation reactions of alkylboronates
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The radical hydroxylation of B-alkylcatecholboranes, easily prepared by hydroboration of olefins, has been investigated. When molecular oxygen was used as oxidizing agent, the corresponding alcohols were obtained directly without alkaline treatment. The presence of Lewis base additives such as Et3N or DABCO has a benefic effect on the selectivity and yield. Alternatively, 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) reacts cleanly with B-alkylcatecholboranes to afford alkyl radicals that can be trapped by a second equivalent of TEMPO to give alkoxyamines. Reduction of the alkoxyamines with zinc in acetic acid affords the desired alcohols. The whole procedure is particularly mild and does not require any basic condition. The two approaches presented in this paper are valuable and represent mild alternatives to the classical alkaline oxidation of organoboranes to alcohols.
- Cadot, Christine,Dalko, Peter I.,Cossy, Janine,Ollivier, Cyril,Chuard, Rachel,Renaud, Philippe
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p. 7193 - 7202
(2007/10/03)
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- Asymmetric synthesis of CDP840 by Jacobsen epoxidation. An unusual syn selective reduction of an epoxide
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An asymmetric synthesis of the PDE IV inhibitor, CDP840 (3) is reported. The absolute stereochemistry was controlled by a Jacobsen epoxidation of the Z triaryl olefin 8 (89% ee) or the E triaryl olefin 9 (48% ee). The disparate results in stereocontrol were interpreted in terms of the 'skewed side-on approach model' proposed by Jacobsen. LiBH4 · BH3 reduction of the epoxides was found to proceed with retention of configuration.
- Lynch,Choi,Churchill,Volante,Reamer,Ball
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p. 9223 - 9228
(2007/10/03)
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- Diastereoselective reduction of cyclohexanones with diisobutylaluminium phenoxides in terms of the isoinversion principle
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The diastereoselectivity of the reduction of 2-substituted cyclohexanones 1-6 with 4-substituted diisobutylaluminium phenoxides a-d has been investigated as a function of temperature. The high-temperature region is found to be dominated by hydride transfer, which is controlled by steric as well as electronic effects. However, at low temperatures the Meerwein-Ponndorf-Verley reaction gains in Importance. This phenomenon is quantified by an isoinversion relationship.
- Meyer-Stork, Markus A.,Haag, Dieter,Scharf, Hans-Dieter
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p. 593 - 595
(2007/10/03)
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- Silica Gel Supported Zinc Borohydride. A Novel Reagent for Hydration of Unactivated Alkenes and Alkynes
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A simple and general procedure for hydration of unactivated alkenes and alkynes producing less substituted alcohols selectively has been achieved by the reaction of the corresponding alkenes or alkynes on silica gel support with zinc borohydride in 1,2-dimethoxyethane.
- Ranu, Brindaban C.,Sarkar, Arunkanti,Saha, Manika,Chakraborty, Rupak
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p. 6579 - 6584
(2007/10/02)
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- An Unusual Anti-Markovnikov Hydration of Alkenes with Titanium(III) Tetrahydroborates
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Titanium(III) tetrahydroborate formed by the reaction of titanium tetrachloride and benzyltriethylammonium borohydride (1:4) reacts with alkenes in dichloromethane (-20 deg C) very readily to yield directly the corresponding alcohols in excellent yields after a simple aqueous work up.
- Kumar, K. S. Ravi,Baskaran, S.,Chandrasekaran, S.
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p. 171 - 174
(2007/10/02)
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- An unusual regioselctive anti-Markovnikov hydration of alkenes with zinc borohydride on silica gel support
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An efficient and general procedure of regioselective anti-Markovnikov hydration of alkenes producing less-substituted alcohols has been achieved by a simple reaction of alkene on silica gel support with zinc borohydride in 1,2-dimethoxyethane.
- Ranu,Chakraborty,Saha
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p. 4659 - 4662
(2007/10/02)
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- An Internally Activated Tin Hydride with Enhanced Reducing Ability
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Tin hydride 1 is activated for nucleophilic hydride transfer and also for radical chain reduction, depending on solvent.The nucleophilic hydride pathway is favored in methanol, and 1 can be used as a selective reducing agent for ketones.Simple ketones are not reduced in aprotic solvents, but β-hydroxy ketones are activated internally by the hydroxyl group and can be reduced in THF with good control of stereochemistry, as in the conversion from 7 to 9 (30:1 9:8).A catalytic version of the nucleophilic hydride reductions in methanol has been developed using PhSiH3 as the stoichiometric hydride source.Radical chain dehalogenations can also be achieved with 1 at room temperature and without added radical initiators.Simple xanthates are not reduced efficiently in the absence of an initiator, but the reaction proceeds in the presence of AIBN.
- Vedejs, E.,Duncan, S. M.,Haight, A. R.
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p. 3046 - 3050
(2007/10/02)
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- Stereoselectivity in hydrosilylative reduction of substituted cyclohexanone derivatives with chiral rhodium-bis(oxazolinyl)pyridine catalyst
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Stereoselectivity in the reduction of substituted cyclohexanones, 4-tert-butylcyclohexanone, 2-methylcyclohexanone, 2-phenylcyclohexanone, and 2-methoxycarbonyl-methylcyclohexanone, was examined with chiral rhodium-bis(oxazolinyl)pyridine catalyst and diphenylsilane. 4-tert-Butylcyclohexanone gave the corresponding trans(equatorial)-alcohol predominantly; the ratio of the trans/cis alcohols, 67:33. Other 2-substituted cyclohexanones showed exclusive enantioselectivities for each diastereomer in terms of the kinetic resolution; e.g. from 2-phenylcyclohexanone, 99% ee of (1S,2R)-trans-2-phenylcyclohexanol and 96% ee of (1S,2S)-cis-2-phenylcyclohexanol in 92% yield (the trans/cis ratio = 51:49).
- Nishiyama,Park,Itoh
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p. 1029 - 1034
(2007/10/02)
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- A Facile Conversion of Alkenes to Alcohols with Benzyltriethylammonium Borohydride-Chlorotrimethylsilane
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A combination of benzyltrimethylammonium borohydride and chlorotrimethylsilane (1:1) in dichloromethane at 0 deg C has been found to be a convenient reagent system for the conversion of alkenes to alcohols, the hydroxy group of which is introduced in an anti-Markovnikov manner.
- Baskaran, Sundarababu,Gupta, Varsha,Chidambaram, Nallaperumal,Chandrasekaran, Srinivasan
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p. 903 - 904
(2007/10/02)
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- ACTIVATION OF REDUCING AGENTS. SODIUM HYDRIDE CONTAINING COMPLEX REDUCING AGENTS 21. REGIOSELECTIVE REDUCTION OF ALKENE OXIDES
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It is shown that epoxides are reduced by ZnCRA and NiCRA.Interestingly, the simple change in the nature of the metal included in the reagent, changes the regiochemistry of the reduction.
- Fort, Yves,Vanderesse, Regis,Caubere, Paul
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p. 3111 - 3114
(2007/10/02)
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- Solvolysis of cis- and trans-2-Phenylcyclohexyl-p-bromobenzene Sulphonate
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Die Solvolyse von cis- and trans-2-Phenyl-cyclohexyl-p-brombenzensulfonaten wurde in Essigsaeure, waessrigem Dioxan und waessrigem Ethanol untersucht und mit der des Cyclohexylsulfonatesters verglichen.In Essigsaeure liegt die Geschwindigkeit des cis-Isomeren gegenueber dem trans-Isomeren um den Faktor 5 hoeher, in waessrigem Dioxan und waessrigem Alkohol dagegen um den Faktor 10 bzw. 12.Produkte der Acetolyse sind hauptsaechlich Eliminierungsprodukte (1- und 3-Phenylcyclohexen 75 percent) und cis- und trans-Acetate (25 percent).In waessrigen Loesungsmitteln entstehen vorwiegend Eliminierungsprodukte (98 percent).Die Erhoehung der Geschwindigkeit des cis-Isomeren gegenueber der trans-Verbindung ist auf eine sterische Beschleunigung zurueckzufuehren.Ein solvatisiertes Ionenpaar wurde als Zwischenprodukt postuliert; fuer eine Phenylnachbargruppenwirkung ergab sich kein Hinweis.
- Youssef, Abdel-Hamid A.,Sharaf, Saber M.,Hegazy, Fatma M. El
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p. 725 - 734
(2007/10/02)
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- Properties of Bis(trifluoroacetoxy)borane as a Reducing Agent of Organic Compounds
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Reactions of bis(trifluoroacetoxy)borane-THF (1) with compounds containing representative organic functional groups were studied to determine the usefulness of 1 as a selective reducing agent.Reducible functionalities were indoles, ketones, aldehydes, imines, and compounds that readily generate carbocations in trifluoroacetic acid.Many functionalities were inert to 1.Epoxides and ortho esters suffered decomposition under the reaction conditions.Olefins and acetylenes were not hydroborated, and carboxylic acids were not reduced by 1.
- Maryanoff, Bruce E.,McComsey, David F.,Nortey, Samuel O.
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p. 355 - 360
(2007/10/02)
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- Formation of Alcohols from Alkenes with TiCl4-NaBH4
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The reaction of alkenes with TiCl4-NaBH4 in 1,2-dimethoxyethane afforded alcohols, the hydroxy group of which was introduced in an anti-Markovnikov direction.
- Kano, Shinzo,Tanaka, Yasuyuki,Hibino, Satoshi
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p. 414 - 415
(2007/10/02)
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