- Reaction of Trialkylboranes with Sodium Diethyldihydroaluminate in the Presence of 1,4-Diazabicyclooctane. A Convenient, General Method for Preparation of Sodium Trialkylborohydrides
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Trialkylboranes in tetrahydrofuran (THF) or diethyl ether (EE) solutions, including those with exceptionally large steric requirements, react readily with toluene solutions of sodium diethyldihydroaluminate in the presence of 1,4-diazabicyclooctane (DABCO) to yield the corresponding sodium trialkylborohydrides and diethylaluminum hydride.The diethylaluminum hydride precipitates from solution as its DABCO adduct, with the use of EE as solvent facilitating the separation.This reaction constitutes a convenient, general method for preparing sodium trialkylborohydrides.
- Hubbard, John L.,Fuller, Joseph C.,Jackson, Thomas C.,Singaram, Bakthan
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- Al-free Zr-zeolite beta as a regioselective catalyst in the Meerwein-Ponndorf-Verley reaction
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Al-free Zr-zeolite beta catalyzes the transfer reduction of ketones to the corresponding alcohols in high yield and with exceptional stereocontrol. Notably, the catalyst is very robust and gives good results even with 10% water content in the reaction mixture.
- Zhu, Yongzhong,Chuah, Gaikhuan,Jaenicke, Stephan
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- Diastereoselectivity in gas-phase hydride reduction reactions of ketones
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The intrinsic diastereoselectivity of the reduction of a series of cyclic ketones by pentacoordinate silicon hydride ions was investigated in the gas phase with the use of the flowing afterglow-triple quadrupole technique. The percent axial reduction of 4-tert-butylcyclohexanone (1), 2-methylcyclohexanone (2), 3,3,5-trimethylcyclohexanone (3), norcamphor (4), 2-tert-butyl-1,3-dioxan-5-one (5), and 2-tert-butyl-1,3-dithian-5-one (6) was determined by collision-induced dissociation experiments. The results show that axial (exo) reduction dominates for 1, 2, and 4, whereas equatorial reduction is dominant for 3, 5, and 6. The trend observed for the reduction diastereoselectivity of compounds 1-4 and 6 matches their condensed-phase behavior; i.e., the percent axial reduction is reduced when steric hindrance of the ketones is increased (1, 99 ± 3%; 2, 68 ± 5; 3, 9 ± 3%). The remarkable consistency of the results obtained in the gas phase and in solution suggests that environmental effects are either unimportant or cancel out and that the reduction diastereoselectivity is a property that can be attributed to the intrinsic nature of the isolated reactants. Qualitatively, the predictions made by Houk et al. regarding the diastereoselectivity of the reduction of 5 and 6 in the gas phase were confirmed, i.e., a preferred equatorial approach of the hydride reducing agent. The preference of compound 5 to undergo equatorial reduction in the gas phase (33 ± 4% axial reduction) contrasts with the almost exclusive. axial reduction reported in solution (93%). This deviation is likely caused by the strong electrostatic repulsion between the nucleophilic hydride reagent and the ring heteroatoms in 5. Compound 6 exhibits an even stronger preference for equatorial reduction (16 ± 4% axial reduction), in agreement with experimental results obtained by others in the condensed phase. Earlier calculations predict an even stronger preference for equatorial reduction. These results are readily rationalized in terms of competition among steric, torsional, and electrostatic effects.
- Artau, Alexander,Ho, Yeunghaw,Kenttaemaa, Hilkka,Squires, Robert R.
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- Chemoselective reduction of saturated aldehydes and ketones over unsaturated carbonyls with bowl-shaped tris(2,6-diphenylbenzyl)tin hydride
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A high chemoselective reduction of saturated aldehydes and ketones in the presence of unsaturated carbonyls (aromatic and α,β-unsaturated carbonyls) has been realized by using the structurally unique, bowl-shaped tris(2,6-diphenylbenzyl)tin hydride (TDTH) under the influence of Me2AlCl or BF3·OEt2 as Lewis acids.
- Sasaki, Kouji,Komatsu, Naoki,Shirakawa, Seiji,Maruoka, Keiji
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- Trans-Selective and Switchable Arene Hydrogenation of Phenol Derivatives
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A trans-selective arene hydrogenation of abundant phenol derivatives catalyzed by a commercially available heterogeneous palladium catalyst is reported. The described method tolerates a variety of functional groups and provides access to a broad scope of trans-configurated cyclohexanols as potential building blocks for life sciences and beyond in a one-step procedure. The transformation is strategically important because arene hydrogenation preferentially delivers the opposite cis-isomers. The diastereoselectivity of the phenol hydrogenation can be switched to the cis-isomers by employing rhodium-based catalysts. Moreover, a protocol for the chemoselective hydrogenation of phenols to cyclohexanones was developed.
- Bergander, Klaus,Glorius, Frank,Heusler, Arne,Wollenburg, Marco
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p. 11365 - 11370
(2020/11/24)
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- Introduction of Cyclopropyl and Cyclobutyl Ring on Alkyl Iodides through Cobalt-Catalyzed Cross-Coupling
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A cobalt-catalyzed cross-coupling between alkyl iodides and cyclopropyl, cyclobutyl, and alkenyl Grignard reagents is disclosed. The reaction allows the introduction of strained rings on a large panel of primary and secondary alkyl iodides. The catalytic system is simple and nonexpensive, and the reaction is general, chemoselective, and diastereoconvergent. The alkene resulting from the cross-coupling can be transformed to substituted cyclopropanes using a Simmons-Smith reaction. The formation of radical intermediates during the coupling is hypothesized.
- Andersen, Claire,Ferey, Vincent,Daumas, Marc,Bernardelli, Patrick,Guérinot, Amandine,Cossy, Janine
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supporting information
p. 2285 - 2289
(2019/03/29)
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- SN2 Reaction of Diarylmethyl Anions at Secondary Alkyl and Cycloalkyl Carbons
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The substitution reaction of the diethyl allylic and propargylic phosphates with Ar2CH anions was applied to sec-alkyl phosphates to compare reactivity and stereoselectivity. However, the substitution took place on the ethyl carbon of the diethyl phosphate group. We then found that the diphenyl phosphate leaving group ((PhO)2PO2) was suited for the substitution at the sec-alkyl carbon. Enantioenriched diphenyl sec-alkyl phosphates with different substituents (Me, Et, iPr) on the vicinal position underwent the substitution reaction with almost complete inversion (>99% enantiospecificity). The substitution reactions of cyclohexyl phosphates possessing cis or trans substituents (Me and/or tBu) at the C4, C3, and C2 positions of the cyclohexane ring were also studied to observe the difference in reactivity among the cis and trans isomers. A transition-state model with the phosphate leaving group ((PhO)2PO2) in the axial position was proposed to explain the difference. This model was supported by computational calculation of the virtual substitution reaction of the structurally simpler “dimethyl” cyclohexyl phosphates (leaving group = (MeO)2PO2) with MeLi. Furthermore, the calculation unexpectedly indicated higher propensity of (PhO)2PO2 as a leaving reactivity than alkyl phosphate groups such as (MeO)2PO2 and (iPrO)2PO2.
- Shinohara, Riku,Ogawa, Narihito,Kawashima, Hidehisa,Wada, Kyohei,Saito, Shun,Yamazaki, Takashi,Kobayashi, Yuichi
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p. 1461 - 1478
(2019/01/25)
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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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- Cobalt-Nanoparticles Catalyzed Efficient and Selective Hydrogenation of Aromatic Hydrocarbons
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The development of inexpensive and practical catalysts for arene hydrogenations is key for future valorizations of this general feedstock. Here, we report the development of cobalt nanoparticles supported on silica as selective and general catalysts for such reactions. The specific nanoparticles were prepared by assembling cobalt-pyromellitic acid-piperazine coordination polymer on commercial silica and subsequent pyrolysis. Applying the optimal nanocatalyst, industrial bulk, substituted, and functionalized arenes as well as polycyclic aromatic hydrocarbons are selectively hydrogenated to obtain cyclohexane-based compounds under industrially viable and scalable conditions. The applicability of this hydrogenation methodology is presented for the storage of H2 in liquid organic hydrogen carriers.
- Murugesan, Kathiravan,Senthamarai, Thirusangumurugan,Alshammari, Ahmad S.,Altamimi, Rashid M.,Kreyenschulte, Carsten,Pohl, Marga-Martina,Lund, Henrik,Jagadeesh, Rajenahally V.,Beller, Matthias
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p. 8581 - 8591
(2019/09/12)
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- An efficient FeCl3-mediated approach for reduction of ketones through N-heterocyclic carbene boranes
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An efficient FeCl3-mediated approach for reduction of ketones by NHC-BH3 has been developed. A series of ketones were smoothly converted to the corresponding alcohols in good to excellent yields through NHC-BH3 reductive process.
- Wang, Ming-Hui,Chen, Ling-Yan
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supporting information
p. 732 - 735
(2017/03/31)
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- Ruthenium Nanoparticles Stabilized in Cross-Linked Dendrimer Matrices: Hydrogenation of Phenols in Aqueous Media
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Novel catalysts consisting of ruthenium nanoparticles encapsulated in cross-linked matrices based on the poly(propylene imine) dendrimers of the 1st and 3rd generations have been synthesized with a narrow particle size distribution (3.8 and 1.0 nm, respectively). The resulting materials showed high activity for the hydrogenation of phenols in aqueous media (specific catalytic activity reached turnover frequencies of 2975h-1 with respect to hydrogen uptake). It has been shown that the use of water as a solvent leads to a 1.5 to 50-fold increase in the reaction rate depending upon the nature of the substrate. It has been established that unlike the traditional heterogeneous catalysts based on ruthenium, during the hydrogenation of dihydroxybenzenes, the hydrogenation rate decreases in the order: resorcinol>hydroquinoneacatechol. The maximum specific activity for resorcinol was a turnover frequency of 243150h-1 with respect to hydrogen uptake. The catalyst based on the dendrimer of the 3rd generation containing finer particles has significantly inferior activity to the catalyst based on the dendrimer of the 1st generation by virtue of steric factors, as well as the need for prereduction of the ruthenium oxide contained on the surface. These catalysts showed resistance to metal leaching and may be reused several times without loss of activity.
- Maximov, Anton,Zolotukhina, Anna,Murzin, Vadim,Karakhanov, Edward,Rosenberg, Edward
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p. 1197 - 1210
(2015/04/14)
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- Identifying the roles of amino acids, alcohols and 1,2-diamines as mediators in coupling of haloarenes to arenes
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Coupling of haloarenes to arenes has been facilitated by a diverse range of organic additives in the presence of KOtBu or NaOtBu since the first report in 2008. Very recently, we showed that the reactivity of some of these additives (e.g., compounds 6 and 7) could be explained by the formation of organic electron donors in situ, but the role of other additives was not addressed. The simplest of these, alcohols, including 1,2-diols, 1,2-diamines, and amino acids are the most intriguing, and we now report experiments that support their roles as precursors of organic electron donors, underlining the importance of this mode of initiation in these coupling reactions.
- Zhou, Shengze,Doni, Eswararao,Anderson, Greg M.,Kane, Ryan G.,Macdougall, Scott W.,Ironmonger, Victoria M.,Tuttle, Tell,Murphy, John A.
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supporting information
p. 17818 - 17826
(2015/02/19)
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- Cytochrome P450 catalyzed oxidative hydroxylation of achiral organic compounds with simultaneous creation of two chirality centers in a single C-H activation step
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Regio- and stereoselective oxidative hydroxylation of achiral or chiral organic compounds mediated by synthetic reagents, catalysts, or enzymes generally leads to the formation of one new chiral center that appears in the respective enantiomeric or diastereomeric alcohols. By contrast, when subjecting appropriate achiral compounds to this type of C-H activation, the simultaneous creation of two chiral centers with a defined relative and absolute configuration may result, provided that control of the regio-, diastereo-, and enantioselectivity is ensured. The present study demonstrates that such control is possible by using wild type or mutant forms of the monooxygenase cytochrome P450 BM3 as catalysts in the oxidative hydroxylation of methylcyclohexane and seven other monosubstituted cyclohexane derivatives.
- Roiban, Gheorghe-Doru,Agudo, Ruben,Reetz, Manfred T.
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supporting information
p. 8659 - 8663
(2014/08/18)
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- Reductions of aldehydes and ketones with a readily available N-heterocyclic carbene borane and acetic acid
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Acetic acid promotes the reduction of aldehydes and ketones by the readily available N-heterocyclic carbene borane, 1,3-dimethylimidazol-2-ylidene borane. Aldehydes are reduced over 1-24 h at room temperature with 1 equiv of acetic acid and 0.5 equiv of the NHC-borane. Ketone reductions are slower but can be accelerated by using 5 equiv of acetic acid. Aldehydes can be selectively reduced in the presence of ketones. On a small scale, products are isolated by evaporation of the reaction mixture and direct chromatography.
- Lamm, Vladimir,Pan, Xiangcheng,Taniguchi, Tsuyoshi,Curran, Dennis P.
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p. 675 - 680
(2013/05/21)
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- Transition-metal-free synthesis of pinacol alkylboronates from tosylhydrazones
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Highly efficient: Pinacol alkylboronates were synthesized by the reaction of tosylhydrazones with bis(pinacolato)diboron or pinacolborane under transition-metal-free conditions. This reaction represents an expeditious conversion of carbonyl functionality into a boronate group. Copyright
- Li, Huan,Wang, Long,Zhang, Yan,Wang, Jianbo
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supporting information; experimental part
p. 2943 - 2946
(2012/04/18)
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- Hydrogen-transfer reduction of carbonyl compounds promoted by nickel nanoparticles
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Nickel(0) nanoparticles, generated from nickel(II) chloride, lithium powder and a catalytic amount of 4,4-di-tert-butylbiphenyl (DTBB) in THF at room temperature, have been found to promote the reduction of a variety of ketones and aldehydes by transfer hydrogenation using isopropanol as the hydrogen donor. The nickel nanoparticles were characterised and could be re-utilised with a good performance in the absence of a base. A mechanistic study demonstrates that the reaction proceeds through a dihydride-type mechanism.
- Alonso, Francisco,Riente, Paola,Yus, Miguel
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p. 1847 - 1852
(2008/09/18)
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- Hydrogen-transfer reduction of carbonyl compounds catalysed by nickel nanoparticles
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We report for the first time the hydrogen-transfer reduction of carbonyl compounds catalysed by well-defined nickel(0) nanoparticles. The nickel nanoparticles could be reutilised several times in a very simple reaction medium composed of the nickel nanoparticles, isopropanol and the substrate, without any added base.
- Alonso, Francisco,Riente, Paola,Yus, Miguel
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p. 1939 - 1942
(2008/09/19)
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- Stereoselective hydrogenation of tert-butylphenols over charcoal-supported rhodium catalyst in supercritical carbon dioxide solvent
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Hydrogenation of 2-, 3-, and 4-tert-butylphenols was studied over a charcoal-supported rhodium catalyst in supercritical carbon dioxide (scCO2) solvent, and the results were compared with those in organic solvents. In the hydrogenation of 4-ter
- Hiyoshi, Norihito,Rode, Chandrashekhar V.,Sato, Osamu,Tetsuka, Hiroyuki,Shirai, Masayuki
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- Stereoselective cascade hydrogenation of 4-tert-butylphenol and p-cresol over Zr-zeolite beta-supported rhodium
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The hydrogenation of 4-tert-butylphenol and p-cresol was investigated over Zr-beta-supported rhodium catalysts. By designing a suitable bifunctional catalyst, the intermediate, 4-alkylcyclohexanone, formed by metal-catalyzed hydrogenation of 4-alkylphenol, could be reduced via the highly stereoselective Meerwein-Ponndorf-Verley reduction over zirconium Lewis acid sites. Thus, in the presence of 2-propanol as solvent and MPV reductant, a high stereoselectivity to cis-4-alkylcyclohexanol was observed. Over 0.5% Rh/Zr-beta, 4-tert-butylphenol, and p-cresol were hydrogenated to the cis-alcohols with 95 and 89% stereoselectivity, respectively. A higher metal loading or the use of solvents such as hexane or tert-butanol led to a lower stereoselectivity, as metal-catalyzed hydrogenation predominated. Similarly, the cis:trans alcohol ratio was lower for rhodium supported on zirconia or Al-beta. Compared with rhodium, palladium was less active in the hydrogenation of the 4-alkylphenols, requiring a higher hydrogen pressure and temperature. A two-step cascade reaction mechanism is proposed for the conversion of 4-alkylphenols to cis-4-alkylcyclohexanols.
- Nie, Yuntong,Jaenicke, Stephan,van Bekkum, Herman,Chuah, Gaik-Khuan
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p. 223 - 231
(2008/03/13)
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- Control of stereoselectivity in 4-tert-butylphenol hydrogenation over a carbon-supported rhodium catalyst by carbon dioxide solvent
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cis-4-tert-Butylcyclohexanol was obtained with a high cis ratio (cis/(cis + trans) = 0.9) in the hydrogenation of 4-tert-butylphenol over a carbon-supported rhodium catalyst along with hydrochloric acid in supercritical carbon dioxide solvent. Copyright
- Hiyoshi, Norihito,Mine, Eiichi,Rode, Chandrashekhar V.,Sato, Osamu,Ebina, Takeo,Shirai, Masayuki
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p. 1060 - 1061
(2007/10/03)
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- Chemo- and regioselective Meerwein-Ponndorf-Verley and Oppenauer reactions catalyzed by Al-free Zr-zeolite beta
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Al-free Zr-beta zeolite with Si/Zr up to 75 was synthesized in a fluoride medium. The incorporation of zirconium into zeolite beta induced the formation of increased amounts of polymorph B. Lewis acid sites were predominant in the Al-free Zr-beta. Zr-zeolite beta was an excellent catalyst in the Meerwein-Ponndorf-Verley (MPV) reduction of several alkyl- and aryl-substituted cyclohexanones, with high selectivity to the corresponding alcohols. The catalyst was reusable and no leaching was detected under the reaction conditions. A prominent feature of the Zr-zeolite beta catalyst was its ability to maintain activity even in the presence of rather significant amounts of water, ≤ 9 wt%. The high catalytic ability of Zr-beta zeolites for the MPV reaction was attributed to the presence of Lewis acid sites with appropriate acid strength and to the ease of ligand exchangeability of Zr. Zr-zeolite beta had predominantly Lewis acidity with higher Lewis acid strength than that of Ti- and Sn-zeolite beta, which enabled Zr-zeolite beta to bind the carbonyl group effectively. Regeneration of the catalyst after poisoning by benzoic acid can be effected by thorough washing with 2-propanol. The sample showed good tolerance to the presence of water and pyridine.
- Zhu, Yongzhong,Chuah, Gaikhuan,Jaenicke, Stephan
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- Al-isopropoxydiisobutylalane: A study of the effect of solvent on the rate and stereoselectivity of cyclic ketone reduction
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The effect of solvent on the rate and stereoselectivity of cyclic ketone reduction by Al-isopropoxydiisobutylalane (DIBAiOPr) has been investigated. In dichloromethane, DIBAiOPr behaves as a bulky reducing agent, approaching the carbonyl group along an equatorial trajectory to produce the axial alcohol with > 10:1 stereoselectivity. In sharp contrast, reduction in toluene gives the complementary outcome, affording the thermodynamically more stable isomer with > 99:1 stereoselectivity.
- Bahia, Perdip S.,Jones, Matthew A.,Snaith, John S.
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p. 9289 - 9291
(2007/10/03)
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- Gas-phase hydrogenation of 4-tert-butylphenol over Pt/SiO2
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Gas-phase hydrogenation of 4-tert-butylphenol (4-TBP) over 1% Pt/SiO 2 to cis and trans 4-tert-butylcyclohexanol (4-TBCHOL), via the intermediate 4-tert-butylcyclohexanone, was studied in a differential reactor at atmospheric pressure and at temperatures between 127 and 227°C. The formation of by-products due to hydrogenolysis played an important role in the reaction at temperatures over 200°C. The rates of 4-t-butylcyclohexanol and 4-t-butylcyclohexanone formation passed through a maximum at 187°C. The catalyst deactivation was also considerable. Being thermodynamically more stable the trans form of the alcohols isomers is produced in separate experiments by epimerization in the presence of hydrogen as an astoichiometric compound. The reaction network for the reaction is proposed.
- Kalantar, Ahmad,Backman, Henrik,Carucci, Jose H.,Salmi, Tapio,Murzin, Dmitry Yu.
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- A free radical method for reduction of cyclohexanones - Preferential formation of equatorial alcohols
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Cyclohexanones react with 2-hydroselenobenzoic acid to afford spiro-[4H-3,1-benzoxaselenin-2,1′-cyclohexan]-4-ones. Stannane reduction and basic hydrolysis gives epimeric cyclohexanols, with the equatorial isomer predominating.
- Clive, Derrick L. J.,Cheng, Hua
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p. 1951 - 1961
(2007/10/03)
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- Low-temperature x-ray structural studies of the ester and ether derivatives of cis- and trans-4-tert-butyl cyclohexanol and 2-adamantanol: Application of the variable oxygen probe to determine the relative σ-donor ability of C-H and C-C bonds
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Results of low-temperature X-ray structural studies for five cis-, and three trans-4-tert-butyl cyclohexanol, and six 2-adamantanol ester and ether derivatives are reported. Plots of C-OR bond distance against pKa(ROH) for derivatives of axial alcohol (5), equatorial alcohol (6) and 2-adamantanol derivatives (7) give slopes of -2.77 × 10-3, -2.86 × 10-3 and -3.05 × 10-3, respectively. Given that the relative differences in the slopes are modest, no clear distinction can be made about the relative σ-donor ability of a C-H bond and a C-C bond.
- Spiniello, Marisa,White, Jonathan M.
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p. 3094 - 3101
(2007/10/03)
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- Processes for the preparation of alcohols
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Alcohols are produced in a practical and advantageous method, by the hydrogenation of a carbonyl compound under mild conditions, by reacting the carbonyl compounds with hydrogen in the presence of a bipyridyl derivative, a group VIII transition metal complex, and a base, or by reducing a carbonyl compound in the presence of a bipyridyl derivative, a group VIII transition metal complex, a base, and an alcoholic solvent.
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- Preparation and use of sterically hindered organobis(2,4,6-triisopropylphenyl)hydroborates and their polystyrene derivatives for the diastereoselective reduction of ketones
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Preparations of benzyl and phenylbis(2,4,6-triisopropylphenyl)hydroborates [organoditripylhydroborates] are outlined. The lithium and potassium benzylditripylhydroborates reduce substituted cyclohexanones with diastereoselectivities comparable to those obtained with the most selective reagents known (eg. 99% cis-4-methylcyclohexanol from 4-methylcyclohexanone). Lithium phenylditripylhydroborate also reduces ketones with significant selectivity. For example, 4-methylcyclohexanone is reduced to cis-4-methylcyclohexanol in 88% isomeric purity. Unlike with most other highly selective reagents the reactions take place at room temperature and have the additional advantage that the boron reagent can be recovered quantitatively. Coupling of Merrifield's resin with ditripylfluoroborane in the presence of lithium naphthalenide affords (ditripylborylmethyl)polystyrene. Similarly, coupling of bromopolystyrene with ditripylfluoroborane in the presence of n-BuLi affords (ditripylboryl)polystyrene. Reactions of these polymeric organoboranes with t-BuLi give the corresponding polymer-supported lithium hydroborates. Lithium ditripylhydroboratylmethylpolystyrene reduces cyclic ketones in identical fashion to its non-polymeric counterpart, giving the corresponding thermodynamically less stable alcohols in 99% or better isomeric purity. Similarly, lithium ditripylhydroboratylpolystyrene behaves like its non-polymeric counterpart and reduces 4-methylcyclohexanone to cis-4-methylcyclohexanol in 89% isomeric purity. Recovery and reuse of the organoboranes are even easier for the polymeric reagents. The Royal Society of Chemistry 1999.
- Smith, Keith,El-Hiti, Gamal A.,Hou, Duanjie,DeBoos, Gareth A.
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p. 2807 - 2812
(2007/10/03)
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- Process for producing cis-4-t-butylcyclohexanol
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A process whereby 4-t-butylcyclohexanol with a high content of the cis-isomer, which is useful as a perfume ingredient, can be economically produced on an industrially available scale at a low cost. The process comprises hydrogenating 4-t-butylcyclohexanone by using a specific ruthenium-phosphine complex as a catalyst in the presence of a base containing an alkali metal and an alkylenediamine having from 1 to 6 carbon atoms.
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- Interaction of Trimethylsilyl and Trimethylstannyl Substituants with C-O Bonds at the γ Position. Results from X-ray Structural Studies and Solvolysis Studies
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Accurate X-ray structural studies have been carried on the γ-Me3M (M = Si, Sn)-substituted cyclohexyl esters 21-Ns, 22-Ns, 23-Ns, 21-PNB, and 24-PNB. Analysis of the structural parameters reveals that the C(alkyl)-O(ester) bond distance is lengthened slightly compared to nonmetal- substituted analogues provided that the C-M, C-O, and intervening C-C bonds are in the W arrangement as is the case for 22-Ns, 23-Ns, and 24-Ns. However, the C-O bond distances for 22-PNB and 22-Ns, which do not have the W geometry, are not significantly lengthened. These structural effects are consistent with the presence of a percaudel interaction between the back lobe of the C-M σ bond and the C-O σ* orbital. The γ-Me3Sn cyclohexyl nosylates 21-Ns and 23-Ns undergo unimolecular solvolysis in 97% TFE/H2O with relative rates ca. 1:>10 000.
- Green, Alison J.,Pigdon, Tracey,White, Jonathan M.,Yamen, Joseph
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p. 3943 - 3951
(2007/10/03)
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- New clay-supported chiral rhodium complexes: Interlayer modification with structural tuning guests and asymmetric hydrogenation
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The novel host-guest catalysts, in which a chiral rhodium complex was intercalated into structural tuning guests modified smectites, were synthesized, and drastic change in catalysis was observed depending on the orientation of guest molecules.
- Sento, Tadashi,Shimazu, Shogo,Ichikuni, Nobuyuki,Uematsu, Takayoshi
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p. 1191 - 1192
(2007/10/03)
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- Reaktionen von Ph2SbH und p-TolSbH2 mit organischen Verbindungen
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p-TolSbH2 reacts with styrene with formation of ethylbenzene and (p-TolSb)n (n=4, 5 in benzene). The action of phenyl acetylene on p-TolSbH2 gives styrene. Addition of Ph2SbH on phenyl acetylene in the presence of AIBN (azodiisobutyronitrile) yields 95% trans- and 5% cis-PhCH=CHSbPh2. Ph2SbH reacts with benzaldehyde in the presence of AIBN with formation of benzylalcohol (98%) and with various prochiral ketones in the presence of chiral auxiliares to give alcohols in high optical yields. Benzotrichloride reacts with Ph2SbH in the presence of PdCl2 to give benzylidene chloride. 1-Bromo adamantane, dibromo cholestanol, 2-chloro acetophenone, cinnamic acid chloride, and chloro acetophenone react with Ph2SbH/AIBN with substitution of the halogen atoms by hydrogen. Benzylbenzoate is formed the by action of Ph2SbH/AIBN on benzoyl chloride.
- Breunig,Probst
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p. 297 - 303
(2007/10/03)
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- Chemoselectivity of lithium aluminium hydride-(±)threo-1,16- dibenzyloxy,7,8-dihydroxy hexadecane-methanol complex in reduction of carbonyl compounds
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Modification of lithium aluminum hydride(LAH) with (±)-threo-1,16- dibenzyloxy,7,8-dihydroxy hexadecane, prepared from (±)-threo- 9,10,16- trihydroxy hexadecanoic acid(aleuritic acid) for chemo- and stereo-selective reduction of carbonyl compounds is reported. Aldehydes were selectively reduced in the presence of a highly reactive cyclohexanone and other ketones. Stereoselectivity in reduction of ketones was observed in cases where high levels of the reagent was used.
- Malkar,Kumar
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p. 977 - 993
(2007/10/03)
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- Reductions of C=O and C=N groups with the systems composed of (η5-C5H5)2MoH2 and acids
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Selective reductions of organic compounds, such as carbonyl compounds and imines, using a system composed of Cp2MoH2 and acids are examined. This system can reduce the substrates under mild conditions. Extremely high diastereoselectivity was achieved in the reduction of 4-t-butylcyclohexanone. The reactivity of imines depends on their structure. Aromatic imines are found to be more reactive than aliphatic imines.
- Minato, Makoto,Fujiwara, Yutaka,Koga, Miho,Matsumoto, Naoya,Kurishima, Susumu,Natori, Makoto,Sekizuka, Norihiro,Yoshioka, Ken-Ichiro,Ito, Takashi
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p. 139 - 145
(2007/10/03)
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- Meerwein-Ponndorf-Verley reduction of carbonyl compounds catalysed by Mg-Al hydrotalcite
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Properly activated Mg-Al hydrotalcite (Mg:Al = 3:1) is found to be a highly active, selective and regenerate heterogeneous catalyst for Meerwein-Ponndorf-Verley reduction of carbonyl compounds in the liquid phase. a On leave from Herdillia Chemicals Ltd., Navi Mumbai, India b figueras@catalyse.univ-lyon1.fr.
- Kumbhar, Pramod S.
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p. 535 - 536
(2007/10/03)
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- trans-[RuCl2(phosphane)2(1,2-diamine)] and chiral trans-[RuCl2(diphosphane)(1,2-diamine: Shelf-stable precatalysts for the rapid, productive, and stereoselective hydrogenation of ketones
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A turnover number (TON) of 2400 000 and a turnover frequency (TOF) of 63 s-1 are achieved with the chiral Ru(II) complex 1 (R = p-CH3C6H4) in the asymmetric hydrogenation of acetophenone. Carbonyl-selective asymmetric hydrogenation of α,β-unsaturated ketones proceeds in the presence of these Ru(II) catalysts, and 4-substituted cyclohexanones are selectively converted into cis alcohols.
- Doucet, Henri,Ohkuma, Takeshi,Murata, Kunihiko,Yokozawa, Tohru,Kozawa, Masami,Katayama, Eiji,England, Anthony F.,Ikariya, Takao,Noyori, Ryoji
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p. 1703 - 1707
(2007/10/03)
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- A mild, convenient, Non-Acidic conversion of enol ethers into alcohols using Hg(OAc)2 - NaBH4
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Alkyl enol ethers can be converted into the corresponding alcohols in good to excellent yields by treatment with aqueous Hg(OAc)2 - NaBH4 in one reaction flask. This method is sufficiently mild to allow the survival of acid-sensitive groups such as silyl ethers, THP-protected alcohols and N-Boc-protected amines.
- Crouch, R. David,Mitten, Jeffrey V.,Span, Amelia R.,Dai, H. George
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p. 791 - 794
(2007/10/03)
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- Reduction of carbonyl compounds by using polymethylhydrosiloxane: Reactivity and selectivity
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Reduction of aldehydes and ketones with PMHS [Me3SiO-(SiMe(H)O)(n)-SiMe3] proceeded smoothly in the presence of Bu4NF at -70°C or 0°C within 60 min in THF. High stereo- and chemoselectivities as well as functional group tolerance of this system are also presented.
- Kobayashi, Yuichi,Takahisa, Eisuke,Nakano, Miwa,Watatani, Kengo
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p. 1627 - 1634
(2007/10/03)
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- Evidence for oxacarbenium ion intermediates in the Lewis acid promoted cleavage of spirocyclic dioxanes
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Studies on the Lewis acid mediated cleavage of spiro-1,3-dioxanes indicate that this process proceeds via an oxacarbenium ion intermediate. With the correct choice of nucleophile and Lewis acid, high selectivities can be obtained.
- Newitt, Lee A.,Steel, Patrick G.
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p. 2033 - 2036
(2007/10/03)
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- Synthesis and Reduction Ability of Borane Complexes of 2-Aminopyridine Derivative having a Chiral Center at the Amino Nitrogen
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A novel method for synthesis of a chiral amine borane is described and selective reductions of carbonyl compounds with the amine borane are investigated.
- Yamaguchi, Yosbimi,Takada, Atsushi,Okamoto, Yosbihisa
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p. 1737 - 1739
(2007/10/03)
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- Sodium borohydride-amberlyst-15 (H+): An effective reductor for hindered and unreactive ketones in aprotic solvent
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The combination of sodium borohydride and amberlyst-15 (H+) in tetrahydrofurane is a powerful reductor for unreactive ketones. The reduction is fast, high-yielding and the work-up is extremely simple. Ketals, silyl ethers and other organic func
- Caycho, Juana Robles,Tellado, Fernando Garcia,De Armas, Pedro,Tellado, Jose Juan Marrero
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p. 277 - 280
(2007/10/03)
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- A Convenient Procedure for the Reduction of Esters, Carboxylic Acids, Ketones and Aldehydes using Tetrabutylammonium Fluoride (or Triton B) and Polymethylhydrosiloxane
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A range of carboxylic esters and acids have been converted efficiently to the corresponding alcohols with polymethylhydrosiloxane in the presence of catalytic tetrabutylammonium fluoride. The reduction of ketones and aldehydes with PMHS and other alkoxysilanes in the presence of TBAF or benzyltrimethylammonium hydroxide is also described.
- Drew, Mark D.,Lawrence, Nicholas J.,Fontaine, David,Sehkri, Lakhdar,Bowles, Stephen A.,Watson, William
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p. 989 - 991
(2007/10/03)
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- cis- and trans-4-tert-butylcyclohexyl p-nitrobenzenesulfonate at 130 K
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The structures of the title axial and equatorial cyclohexyl p-nitrobenzenesulfonate esters, C16H23NO5S, determined at 130 K are reported. The Calkyl-Oester bond distances of 1.487(2) and 1.492 (2) A are not significantly different from one another. The geometry of the sulfonate function with respect to both the phenyl and cyclohexane rings is essentially identical in both structures.
- White, Jonathan M.,Giordano, Josy,Green, Alison J.
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p. 3204 - 3207
(2007/10/03)
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- The importance of entropy in stereoselection. Reduction of tert-butylcyclohexanone by lithium aluminum hydride
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In the title reaction, the differences in both the enthalpy and the entropy of activation between the cis and trans diastereomers were measured (ΔΔH(≠) = -793 (56) cal/mol and ΔΔS(≠) = 2.00 (0.20) e.u.). The experimentally determined ΔΔH(≠) is shown to be
- Rosenberg, Robert E.,Vilardo, Jonathan S.
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p. 2185 - 2188
(2007/10/03)
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- The Biotransformation of 4-tert-Amyl- and 4- tert-Butylcyclohexanone by Cephalosporium aphidicola
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4-tert-Amyl and 4-tert-butylcyclohexanone are shown to be hydroxylated on the 4-substituent by Cephalosporium aphidicola. The carbonyl group is also reduced and the alcohols are also hydroxylated.
- Farooq, Afgan,Hanson, James R.
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p. 104 - 105
(2007/10/03)
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- The Diastereoselectivity of Zirconium Alkoxide Catalysed Meerwein-Ponndorf-Varley Reductions
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The new variation of the Meerwein-Ponndorf-Verley reduction using 1-ethanol (6) or 1-tetralol (12) (3 equiv.) as the reducting alcohols and Zr(OtBu)4 as the catalyst (0.2 equiv.) is kinetically controlled and highly stereoselective.Preferential axial attack is achieved with the sterically less bulky alcohol 6 in the case of 4-tert-butyl- and 3-methylcyclohexanones (1a -> 96percent axial and 3a -> 93percent axial attack).The combination tetralol (12)/Zr(OtBu)4 behaves as a very bulky reducting agent, and the thermodynamically less stable alcohols 2c (80percent) and 4c (92 - 96percent) are formed preferentially in the reduction of 2a and 4b.The fused bicyclic systems 1-methyl-2-tetralone (14a) and flavanone (15a) and the steroids 16a-18a are reduced with high stereoselectivity to the corresponding cis alcohols 14b and 15b and the β-alcohols 16b-18b.The stereochemical outcome is in agreement with the Felkin-Ahn model. - Key Words: Reduction / Meerwein-Ponndorf-Verley reduction / Catalysis / Zirconium tetra-tert-butoxide / Stereochemistry / Diastereoselectivity / Felkin-Ahn model
- Krohn, Karsten,Knauer, Birgit
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p. 1347 - 1352
(2007/10/02)
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- Stereoselective Reduction of 4-tert-Butylcyclohexanone to cis-4-tert-Butylcyclohexanol catalysed by Zeolite BEA
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Zeolite BEA is found to be the first stereoselective and regenerable heterogeneous catalyst for the Meerwein-Ponndorf-Verley reduction of 4-tert-butylcyclohexanone to cis-4-tert-butylcyclohexanol.
- Creyghton, Edward J.,Ganeshie, Soesiela D.,Downing, Roger S.,Bekkum, Herman van
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p. 1859 - 1860
(2007/10/02)
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- Lithium hydride containing complex reducing agent: A new and simple activation of commercial lithium hydride
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Commercially available lithium hydride, an essentially inert metal hydride, can be activated as a hydride source by in situ generated lithium alkoxide in the presence of a nickel salt. The obtained new reagent exhibited reducing properties versus alkyl or aryl halides, ketones, ethylenic or sulfurated compounds as well as coupling properties versus aryl halides when prepared in the presence of a ligand.
- Fort, Yves
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p. 6051 - 6054
(2007/10/02)
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- Preparation and reactivity of chiral β-amino-alkylzinc iodides and related configurationally stable zinc organometallics
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Several zinc organometallics bearing at the β-position a carbamate or an amido function with an acidic N-H group were prepared using the direct insertion of zinc dust into the corresponding alkyl iodides in THF or THF:DMSO mixtures. Most of the starting iodides were obtained from natural α-amino acids and the resulting zinc species afforded after transmetalation with CuCN.2LiCl and reaction with a selection of relatively reactive electrophiles a variety of polyfunctional 1,2-amino alcohol derivatives and carbamates in optically pure form. Several secondary β-amido alkyl iodides were converted to the corresponding chiral zinc reagents and trapped with electrophiles. The configurational stability of chiral secondary organozinc compounds and the stereochemical course of their reactions were examined.
- Duddu,Eckhardt,Furlong,Knoess,Berger,Knochel
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p. 2415 - 2432
(2007/10/02)
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