- Aza-crown compounds synthesised by the self-condensation of 2-amino-benzyl alcohol over a pincer ruthenium catalyst and applied in the transfer hydrogenation of ketones
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A well-defined PNN-Ru catalyst was revisited to self-condense 2-aminobenzyl alcohol in forming a series of novel aza-crown compounds [aza-12-crown-3 (1), aza-16-crown-4 (2) and aza-20-crown-5 (3)]. All aza-crown compounds are separated and determined by NMR, IR, and ESI-MS spectroscopy as well as X-ray crystallography, indicating the saddle structure of 1 and the twisted 1,3-alternate conformation structure of 3. These aza-crown compounds have been explored to study ferric initiation of transfer hydrogenation (TH) of ketones into their corresponding secondary alcohols in the presence of 2-propanol with a basic t-BuOK solution, achieving a high conversion (up to 95%) by a ferric complex with 2 in a low loading (0.05 mol%). This journal is
- Zhang, Shanshan,Wang, Zheng,Cao, Qianrong,Yue, Erlin,Liu, Qingbin,Ma, Yanping,Liang, Tongling,Sun, Wen-Hua
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supporting information
p. 15821 - 15827
(2020/11/24)
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- Catalytic hydrosilylation of ketones using a Co/Zr heterobimetallic complex: Evidence for an unusual mechanism involving ketyl radicals
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The tris(phosphinoamide)-linked heterobimetallic Co/Zr complex (THF)Zr(MesNPiPr2)3CoN2 (1) has been investigated as a catalyst for the hydrosilylation of ketones with PhSiH 3. Catalytic activity superior to monometallic Co or Zr analogues has been observed, demonstrating the importance of cooperative reactivity between Co and Zr. Upon examining stoichiometric reactions, complex 1 was found to be unreactive toward PhSiH3, implying that the mechanism diverges from the typical Chalk-Harrod-type hydrosilylation pathway. In contrast, 1 reacts readily with ketones, and in the case of benzophenone, a radical coupling product [(Ph2CO)Zr(MesNPiPr2) 3CoN2]2 (3) was isolated, implying the intermediacy of a Zr-bound ketyl radical fragment. A radical-based hydrosilylation mechanism is proposed involving hydrogen atom transfer from PhSiH3 to the Zr-bound ketyl-radical.
- Zhou, Wen,Marquard, Seth L.,Bezpalko, Mark W.,Foxman, Bruce M.,Thomas, Christine M.
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p. 1766 - 1772
(2013/05/08)
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- Heterogeneous enantioselective hydrogenation in a continuousflow fixed-bed reactor system: Hydrogenation of activated ketones and their binary mixtures on pt-alumina-cinchona alkaloid catalysts
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Under the experimental conditions of the Orito reaction the individual hydrogenation and the competitive hydrogenations of three binary mixtures of methyl benzoylformate (MBF), pyruvic aldehyde dimethyl acetal (PA) and 2,2-diethoxyacetophenone (DAP) on platinum-alumina catalysts modified by cinchonidine, cinchonine, quinine and quinidine (Pt-CD, Pt-CN, Pt-QN, Pt-QD) were studied for the first time using continuous-flow fixed-bed reactor system. Conversions of chiral (Cc) and racemic (Cr) hydrogenations of all three compounds and enantioselectivities (ee) were determined under the same experimental conditions (under 4 MPa H2 pressure, at room temperature using toluene/AcOH 9/1 as solvent).The order of the rates of the enantioselective hydrogenations of the three substrates studied is MBF > PA > DAP, and the order of their ee values is MBF ? PA > DAP. The hydrogenation rate and the effect of rate on ee depend on the structure of the cinchona used: hydrogenation of MBF and PA may produce ee values over 90 %, however, the ee values were conspicuously low in the presence of Pt-QN and especially of Pt-QD catalysts. In the chiral hydrogenation of DAP considering racemic hydrogenation rate decrease (Cc/Cr 1) takes place instead of rate enhancement over all four catalysts. The new experimental data supported the so far known fundamental rules of the Orito reaction based on batch studies. Springer Science+Business Media, LLC 2012.
- Sz?ll?si, Gyo?rgy,Makra, Zsolt,Fekete, Mónika,Fül?p, Ferenc,Bartók, Mihály
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experimental part
p. 889 - 894
(2012/10/18)
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- O -substituted alkyl aldehydes for rhodium-catalyzed intermolecular alkyne hydroacylation: The utility of methylthiomethyl ethers
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Combining α-methylthiomethyl (MTM) ether substituted aldehydes and 1-alkynes in the presence of [Rh(dppe)]ClO4 results in efficient intermolecular alkyne hydroacylation to deliver α-O-MTM-substituted enone products. The product MTM ethers can be converted to the free hydroxyl group either in situ, by the addition of water to the completed reaction, or in a separate operation, by the action of silver nitrate.(Figure Presented)
- Parsons, Scott R.,Hooper, Joel F.,Willis, Michael C.
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supporting information; experimental part
p. 998 - 1000
(2011/05/15)
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- Zinc(II)-catalyzed addition of grignard reagents to ketones
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(Figure presented) The addition of organometallic reagents to carbonyl compounds has become a versatile method for synthesizing tertiary and secondary alcohols via carbon-carbon bond formation. However, due to the lack of good nucleophilicity or the presence of strong basicity of organometallic reagents, the efficient synthesis of tertiary alcohols from ketones has been particularly difficult and, thus, limited. We recently developed highly efficient catalytic alkylation and arylation reactions to ketones with Grignard reagents (RMgX: R = alkyl, aryl; X = Cl, Br, I) using ZnCl2, Me3SiCH 2MgCl, and LiCl, which effectively minimize problematic side reactions. In principle, RMgBr and RMgI are less reactive than RMgCl for the addition to carbonyl compounds. Therefore, this novel method with homogeneous catalytic ZnCl2·Me3SiCH2MgCl·LiCl is quite attractive, since RMgBr and RMgI, which are easily prepared and/or commercially available, like RMgCl, can be applied successfully. As well as ketones and aldehydes, aldimines were effectively applied to this catalysis, and the corresponding secondary amines were obtained in high yield. With regard to mechanistic details concerning β-silyl effect and salt effect, in situ-prepared [R(Me3SiCH2)2Zn] -[Li]+[MgX2]m[LiCl]n (X = Cl/Br/I) is speculated to be a key catalytic reagent to promote the reaction effectively. The simplicity of this reliable ZnCl2·Me 3SiCH2MgCl·LiCl system in the addition of Grignard reagents to carbonyl compounds might be attractive for industrial as well as academic applications.
- Hatano, Manabu,Ito, Orie,Suzuki, Shinji,Ishihara, Kazuaki
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supporting information; experimental part
p. 5008 - 5016
(2010/10/04)
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- Zinc(ii)-catalyzed Grignard additions to ketones with RMgBr and RMgI
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Highly efficient alkylations and arylations of ketones with Grignard reagents (RMgBr and RMgI) have been developed using catalytic ZnCl2, Me3SiCH2MgCl, and LiCl. Tertiary alcohols were obtained in high yields with high chemoselectivities, while minimizing undesired side products produced by reduction and enolization.
- Hatano, Manabu,Ito, Orie,Suzuki, Shinji,Ishihara, Kazuaki
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scheme or table
p. 2674 - 2676
(2010/07/08)
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- Heterogeneous Enantioselective Hydrogenation of Activated Ketones Catalyzed by Modified Pt-Catalysts: A Systematic Structure-Selectivity Study
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A systematic structure-selectivity study was carried out for the enantioselective hydrogenation of activated ketones with chirally modified Pt/Al2O3 catalysts. For this, 18 modifiers containing an extended aromatic system able to form a strong adsorption complex with the Pt surface, and a suitable chiral group with an amino function capable to interact with the keto group of the substrate (HCd, Qd, HCn, Qn, and semi-synthetic derivatives, as well as synthetic analogues) were prepared and tested on 8 different activated ketones in AcOH and toluene under standard conditions. It was found that relatively small structural changes of the substrate and/or modifier structures strongly affected the enantioselectivity, and that no "best" modifier exists for all substrates. The highest ees for all substrates were obtained with quinuclidine-derived modifiers in combination with naphthalene or quinoline rings, either in AcOH (substrates 1-5 and 8, all carrying an sp3 carbon next to the keto group) or toluene (6 and 7, with an sp2 carbon next to the ketone). The presence and nature of the substituent R′ at the quinuclidine significantly affected the ee (positive and negative effects). Certain combinations of an aromatic system and an amino function were preferred: For the quinuclidine moiety, quinoline and to a somewhat lesser extent naphthalene were a better match, while for the pyrrolidinylmethyl group anthracene was better suited. Methylation of the OH group often had a positive effect for hydrogenations in AcOH but not in toluene. With the exception of 8, higher ees were obtained for the Cd/ Qn series [leading to (R)-products] than for the Cn/ Qd series [leading to (S)-products]. In several cases, opposite structure-selectivity trends were detected when comparing reactions in toluene and AcOH, indicating a significant influence of the solvent.
- Exner, Christian,Pfaltz, Andreas,Studer, Martin,Blaser, Hans-Ulrich
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p. 1253 - 1260
(2007/10/03)
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- Diethoxymethyllithium: generation via transmetallation of diethoxymethyltributyltin, stability, nucleophilic reactivity in addition reactions, and use as a precursor of group 14 formylmetals
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Diethoxymethyltributyltin and bimethoxymethyltributyltin have been converted into the corresponding dialkoxymethyllithium reagents upon transmetallation by n-butyllithium in THF.Temperature appears to be the key parameter controlling the decomposition of diethoxy- (or dimethoxy-) methyllithium.Inside the reactor, -78 deg C appears to be the borderline temperature to allow trapping experiments with electrophiles before decomposition.Nucleophilic addition on carbonyl derivatives has been examined and the evaluation of stereochemical trends and regiochemical trends (1,2-/1,4-addition in the case of α,β-enones) has been used to characterize the chemical behavior of this type of reagent.Furthermore, in the case of electrophilic trapping by chlorosilanes or chlorogermanes, the expected α-silyl or α-germylacetals have been obtained and their hydrolysis into group 14 formylmetals has been observed using electronic spectrometry.Keywords: transmetallation / formylanion equivalent / d1 umpoled reagent / diethoxymethyllithium / nucleophilic reactivity / formylsilanes / formylgermanes / formylstannanes
- Parrain, Jean-Luc,Beaudet, Isabelle,Cintrat, Jean-Christophe,Duchene, Alain,Quintard, Jean-Paul
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p. 304 - 312
(2007/10/02)
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- Substitution of the acetoxy groups of dialkoxymethylacetates by organometallic reagents: a route to allyl-, propargyl-, homoallyl-, homopropargyl- and α-stannylacetals
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The substitution of the acetoxy groups of dialkoxymethylacetates by organometallic reagents has been examined in a search for new methods of preparing functional acetals.The efficiency of the substitution of the acetoxy group is highly dependent on the nature of the organometallic reagents: soft nucleophiles with strong electrophilic assistance by the counterion are the best reagents.Allyl-, propargyl-, homoallyl-, homopropargyl- and α-stannylacetals have been made by this route, in which dialkoxymethylacetates often function as useful substitutes for dialkylphenylorthoformates.
- Beaudet, Isabelle,Duchene, Alain,Parrain, Jean-Luc,Quintard, Jean-Paul
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p. 201 - 212
(2007/10/02)
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