- Chiral-at-Iron Catalyst: Expanding the Chemical Space for Asymmetric Earth-Abundant Metal Catalysis
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A new class of chiral iron catalysts is introduced that contains exclusively achiral ligands with the overall chirality being the result of a stereogenic iron center. Specifically, iron(II) is cis-coordinated to two N-(2-pyridyl)-substituted N-heterocycli
- Hong, Yubiao,Jarrige, Lucie,Harms, Klaus,Meggers, Eric
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supporting information
p. 4569 - 4572
(2019/03/19)
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- Cobalt-Catalyzed Transfer Hydrogenation of α-Ketoesters and N-Cyclicsulfonylimides Using H2O as Hydrogen Source
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A Co-catalyzed effective transfer hydrogenation of various α-ketoesters and N-cyclicsulfonylimides by safe and environmentally benign H2O as hydrogen source is described. The reaction used easily available and easy to handle zinc metal as a reductant. Interestingly, the catalytic system does not require ligand for reduction of N-cyclicsulfonylimides. (Figure presented.).
- Gao, Yang,Zhang, Xuexin,Laishram, Ronibala Devi,Chen, Jingchao,Li, Kangkui,Zhang, Keyang,Zeng, Guangzhi,Fan, Baomin
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p. 3991 - 3997
(2019/08/02)
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- Boron-catalyzed CC functionalization of allyl alcohols
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Tris(pentafluorophenyl)borane-catalyzed CC bond functionalization of arylallyl alcohols using donor-acceptor carbenes is presented. The allylic hydroxyl group is found to assist the product formation by neighboring group participation providing a clue towards mechanistic understanding. This method can also be employed to effect homologation of allyl alcohols to homoallyl alcohols. Overall, this metal-free transformation presents a novel disconnection strategy towards carbon-carbon bond scission and formation.
- Rao, Santhosh,Kapanaiah, Raja,Prabhu, Kandikere Ramaiah
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p. 1301 - 1306
(2019/10/28)
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- Boron-Catalyzed C?C Functionalization of Allyl Alcohols
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Tris(pentafluorophenyl)borane-catalyzed C?C bond functionalization of arylallyl alcohols using donor-acceptor carbenes is presented. The allylic hydroxyl group is found to assist the product formation by neighboring group participation providing a clue towards mechanistic understanding. This method can also be employed to effect homologation of allyl alcohols to homoallyl alcohols. Overall, this metal-free transformation presents a novel disconnection strategy towards carbon-carbon bond scission and formation. (Figure presented.).
- Rao, Santhosh,Kapanaiah, Raja,Prabhu, Kandikere Ramaiah
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supporting information
(2019/02/14)
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- Boron-Catalyzed O-H Bond Insertion of α-Aryl α-Diazoesters in Water
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A catalytic, metal-free O-H bond insertion of α-diazoesters in water in the presence of B(C6F5)3·nH2O (2 mol %) was developed, affording a series of α-hydroxyesters in good to excellent yields. The reaction features easy operation and wide substrate scope, and importantly, no metal is needed as compared with the conventional methods. Significantly, this approach further expands the applications of B(C6F5)3 under water-tolerant conditions.
- San, Htet Htet,Wang, Shi-Jun,Jiang, Min,Tang, Xiang-Ying
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p. 4672 - 4676
(2018/08/09)
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- Zirconocene-catalyzed direct (trans)esterification of acyl acids (esters) and alcohols in a strict 1:1 ratio under solvent-free conditions
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A highly efficient way for the direct (trans)esterification of acyl acids (esters) and alcohols in a strict 1:1 ratio using a zirconocene complex (1, 1 mol%), a strong Lewis acid of good water tolerance, as a catalyst under solvent-free conditions has been developed. A wide range of acid and alcohol (esters) substrates undergo (trans)esterification to produce carboxylic ester motifs in moderate to good or excellent yields with good functional tolerance, such as that towards C-Br as well as CC and CC bonds. And complex 1 can be recycled six times without showing a significant decline in catalytic efficiency. It was demonstrated that cyclandelate, which is used to treat high blood pressure as well as heart and blood-vessel diseases, can be directly synthesized on a gram scale with 81% yield (6.70 g) using complex 1.
- Tang, Zhi,Jiang, Qiutao,Peng, Lifen,Xu, Xinhua,Li, Jie,Qiu, Renhua,Au, Chak-Tong
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supporting information
p. 5396 - 5402
(2017/11/22)
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- Enantio- and chemoselective Br?nsted-acid/Mg(nBu) 2 catalysed reduction of α-keto esters with catecholborane
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The first enantio- and chemoselective Br?nsted-acid catalysed reduction of α-keto esters with catecholborane has been developed. The α-hydroxy esters were obtained under mild reaction conditions in virtually quantitative yields and excellent enantioselectivities. With slight modifications both enantiomers can be obtained without any loss of selectivity. This journal is the Partner Organisations 2014.
- Enders, Dieter,St?ckel, Bianca A.,Rembiak, Andreas
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p. 4489 - 4491
(2014/04/17)
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- Efficient acid-catalyzed conversion of phenylglyoxal to mandelates on flame-derived silica/Alumina
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Amorphous, nonporous silica/alumina (SA) made by flame-spray pyrolysis (FSP) efficiently catalyzes the direct conversion of phenylglyoxal (PG) to alkyl mandelates. The SAs exhibited a turnover frequency more than an order of magnitude higher than dealuminated zeolite Y, which hitherto has been considered as the most active solid acid for this reaction. The free diffusion of PG to surface acid sites and rapid removal of mandelate products are proposed to be at the origin of the superior performance of SAs. The recyclability of the catalyst was tested in five repetitive runs and showed no significant loss of catalyst performance.
- Wang, Zichun,Jiang, Yijiao,Baiker, Alfons,Huang, Jun
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p. 1573 - 1577
(2013/07/26)
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- 1,3-Bis(2,4,6-trimethylphenyl)imidazolium chloride in combination with triethylamine: An improved catalytic system for hydroacylation/reduction of activated ketones
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A rapid, economic, and high yielding methodology has been developed for hydroacylation/reduction of activated ketones by using 1,3-bis(2,4,6- trimethylphenyl)imidazolium chloride as a catalyst in combination with triethylamine. The reaction proceeded at an ambient temperature via generating N-heterocyclic carbene in situ that interacted with the (hetero)aryl aldehyde employed. While the reduction of ketones takes place in MeOH, the hydroacylation process was found to be effective in THF for both electron rich and deficient aldehydes.
- Sreenivasulu,Arun Kumar,Sateesh Reddy,Siva Kumar,Rajender Kumar,Chandrasekhar,Pal, Manojit
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supporting information; experimental part
p. 727 - 732
(2011/03/21)
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- Asymmetric aerobic oxidation of α-hydroxy acid derivatives catalyzed by reusable, polystyrene-supported chiral N-salicylidene oxidovanadium tert-leucinates
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The direct immobilization of two different C-5-propargyl ether-modified, chiral N-salicylidene vanadyl(V) tert-leucinates onto 4-azidomethyl-substituted polystyrene by click chemistry was examined. Among the eight different solvents investigated, the resulting polystyrene-supported catalysts promote the asymmetric, aerobic oxidation of α-hydroxy (thio)esters and amides with enantioselectivities of up to 99% ee (selectivity factor up to 41) in chloroform. These polystyrene-supported catalysts can be readily recovered by filtration and reused for at least four consecutive runs without discernible loss of reactivity and enantioselectivity.
- Salunke, Santosh B.,Babu, N.Seshu,Chen, Chien-Tien
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supporting information; experimental part
p. 1234 - 1240
(2011/06/26)
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- Reduction of aromatic and aliphatic keto esters using sodium borohydride/MeOH at room temperature: a thorough investigation
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Reduction of keto esters is a valuable alternative to produce diols. Sodium borohydride/MeOH system at room temperature and short reaction time efficiently reduced α, β, γ, and δ-keto esters having α-keto esters as the most reactive. The ester functionality was reduced effectively due to the presence of oxo group that somehow facilitates the formation of ring intermediate. As expected, the chemoselective experiments showed that ester functionality was not reduced using this system. This study presents a simple, easy, and benign reduction process of various keto esters to its corresponding diols.
- Kim, Juryoung,De Castro, Kathlia A.,Lim, Minkyung,Rhee, Hakjune
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supporting information; experimental part
p. 3995 - 4001
(2010/07/05)
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- New boron(III)-catalyzed amide and ester condensation reactions
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In 1996, we reported that benzeneboronic acids bearing electron-withdrawing groups at the meta- or para-position are highly effective catalysts for the amide condensation reaction in less-polar solvents. In this paper, we report that N-alkyl-4-boronopyridinium halides are more effective catalysts than the previous ones in more polar solvents. N-Alkyl-4-boronopyridinium halides are effective not only for amide condensation between equimolar mixtures of carboxylic acids and amines but also for the esterification of α-hydroxycarboxylic acids in alcohol solvents. Furthermore, perchlorocatecholborane is more effective than areneboronic acids for the amide condensation of sterically demanding carboxylic acids. In addition, Lewis acid-assisted Br?nsted acid (LBA), which is prepared from a 1:2 M mixture of boric acid and tetrachlorocatechol, is effective for the Ritter reaction from alcohols and nitriles to amides.
- Maki, Toshikatsu,Ishihara, Kazuaki,Yamamoto, Hisashi
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p. 8645 - 8657
(2008/02/08)
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- Ytterbium triflate-promoted tandem one-pot oxidation-cannizzaro reaction of aryl methyl ketones
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(Chemical Equation Presented) Ytterbium triflate was shown to be an effective catalyst in promoting the synthesis of either isopropyl esters or free α-hydroxy-arylacetic acids from substituted aromatic glyoxals and aryl methyl ketones, respectively. The reaction to provide acids starting from differently substituted ketones was carried out by an environmentally friendly method using an aqueous medium as a solvent and giving the adducts in 78-99% yield without any further purification after the usual workup.
- Curini, Massimo,Epifano, Francesco,Genovese, Salvatore,Marcotullio, M. Carla,Rosati, Ornelio
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p. 1331 - 1333
(2007/10/03)
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- N-alkyl-4-boronopyridinium halides versus boric acid as catalysts for the esterification of α-hydroxycarboxylic acids
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(Chemical Equation Presented) Boric acid is a highly effective catalyst for the dehydrative esterification reaction between equimolar mixtures of α-hydroxycarboxylic acids and alcohols. In contrast, N-methyl-4- boronopyridinium iodide (2a) is a more effective catalyst than boric acid for the similar esterification in excess alcohol. A heterogeneous catalyst, such as N-polystyrene-bound 4-boronopyridinium chloride, is also an effective catalyst and can be recovered by filtration.
- Maki, Toshikatsu,Ishihara, Kazuaki,Yamamoto, Hisashi
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p. 5047 - 5050
(2007/10/03)
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- Boric acid catalyzed chemoselective esterification of α- hydroxycarboxylic acids
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Boric acid catalyzes the selective esterification of α- hydroxycarboxylic acids without causing significant esterification to occur with other carboxylic acids. The procedure is simple, high-yielding, and applicable to the esterification of α-hydroxy carboxylates in the presence of other carboxylic acids including β-hydroxyacids within the same molecule.
- Houston, Todd A.,Wilkinson, Brendan L.,Blanchfield, Joanne T.
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p. 679 - 681
(2007/10/03)
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- Rhodium-catalyzed addition of arylstannanes to carbon-heteroatom double bond
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The addition of arylstannanes to the carbon-heteroatom double bond in the presence of a catalytic amount of a cationic rhodium complex ([Rh(cod)(MeCN)2]BF4) was examined. The reactions of aldehydes, α-dicarbonyl compounds, and N-substituted aldimines with the arylstannanes gave corresponding alcohols, α-hydroxy carbonyl compounds, and amines, respectively. An arylrhodium complex generated by the transmetalation with the arylstannane was probably the active catalytic species.
- Oi, Shuichi,Moro, Mitsutoshi,Fukuhara, Hiroe,Kawanishi, Takanori,Inoue, Yoshio
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p. 4351 - 4361
(2007/10/03)
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- YCL3-catalyzed highly selective conversion of arylglyoxal to α-aryl- α-hydroxyacetic ester: Dramatic influence of base
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Yttrium chloride catalyzed reaction of arylglyoxal and alcohol resulted in highly selective formation of α-aryl-α-hydroxyacetic ester under the influence of an added base (triethylamine, pyridine, piperidine) and afforded acetal in the absence of the base. The possible role of the additive (base) is discussed.
- Likhar, Pravin R.,Bandyopadhyay, Ananda K.
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p. 538 - 540
(2007/10/03)
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- Selective esterification of aliphatic nonconjugated carboxylic acids in the presence of aromatic or conjugated carboxylic acids catalysed by NiCl2.6H2O
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Unhindered aliphatic nonconjugated carboxylic acids were esterified selectively in the presence of aromatic or conjugated acids on heating in the corresponding alcoholic solutions at reflux for 3-13 hr with 10 mol% of NiCl2.6H2O catalyst.
- Ram, Ram N.,Charles
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p. 7335 - 7340
(2007/10/03)
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- Synthesis of Chiral α-Aryl-α-Hydroxyacetic Acids: Substituent Effects in Pig Liver Acetone Powder (PLAP) Induced Enantioselective Hydrolysis
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Pig liver acetone powder (PLAP) catalyzed hydrolysis of alkyl α-acetoxy-α-arylacetates produces alkyl (S)-α-aryl-α-hydroxyacetates in 23-80percent enantiomeric purities.Enantioselectivity is dependent on the ester group of O-acetylmandelates.Substitution on the aromatic ring results in inferior selectivities.Only acetate group is hydrolyzed by PLAP while the ester functionality is found to be completely intact.
- Basavaiah, Deevi,Krishna, Peddinti Rama
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p. 2403 - 2416
(2007/10/02)
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- Catalysis by Cobalt Schiff's Base Complexes in Highly Selective Conversion of Arylglyoxals to α-Aryl-α-hydroxyacetic Esters
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Cobalt Schiff's base complexes catalyse highly selective conversion of arylglyoxals to α-aryl-α-hydroxyacetic esters in alcohols; Lewis acidity of CoIII species may be responsible to the catalysis.
- Maruyama, K.,Murakami, Y.,Yoda, K.,Mashino, T.,Nishinaga, A.
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p. 1617 - 1618
(2007/10/02)
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