- Asymmetric synthesis of 9-alkyl tetrahydroxanthenones: Via tandem asymmetric Michael/cyclization promoted by chiral phosphoric acid
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A tandem asymmetric Michael-addition/cyclization of cyclic 1,3-dicarbonyl compounds to β,γ-unsaturated α-ketoesters catalyzed by chiral phosphoric acid is presented. This protocol provides a facile approach for the construction of enantioenriched 9-alkyl tetrahydroxanthenones, an ubiquitous framework found in a number of natural products and pharmaceutical molecules, in high yields with good to high enantioselectivities. This journal is
- Gao, Yu-Qi,Hou, Yi,Chen, Junhan,Zhen, Yanxia,Xu, Dongyang,Zhang, Hongli,Wei, Hongbo,Xie, Weiqing
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supporting information
p. 348 - 354
(2021/01/29)
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- The construction of novel and efficient hafnium catalysts using naturally existing tannic acid for Meerwein-Ponndorf-Verley reduction
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The conversion of carbonyl compounds into alcohols or their derivatives via the catalytic transfer hydrogenation (CTH) process known as Meerwein-Ponndorf-Verley reduction is an important reaction in the reaction chain involved in biomass transformation. The rational design of efficient catalysts using natural and renewable materials is critical for decreasing the catalyst cost and for the sustainable supply of raw materials during catalyst preparation. In this study, a novel hafnium-based catalyst was constructed using naturally existing tannic acid as the ligand. The prepared hafnium-tannic acid (Hf-TA) catalyst was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and thermogravimetry (TG). Hf-TA was applied in the conversion of furfuraldehyde (FD) to furfuryl alcohol (FA) using isopropanol (2-PrOH) as both the reaction solvent and the hydrogen source. Both preparation conditions and the effects of the reaction parameters on the performance of the catalyst were studied. Under the relatively mild reaction conditions of 70 °C and 3 h, FD (1 mmol) could be converted into FA with a high yield of 99.0%. In addition, the Hf-TA catalyst could be reused at least ten times without a notable decrease in activity and selectivity, indicating its excellent stability. It was proved that Hf-TA could also catalyze the conversion of various carbonyl compounds with different structures. The high efficiency, natural occurrence of tannic acid, and facile preparation process make Hf-TA a potential catalyst for applications in the biomass conversion field.
- Deng, Lijuan,Hao, Jianxiu,He, Runxia,Li, Na,Liu, Quansheng,Wang, Xiaolu,Zhao, Hongye,Zhi, Keduan,Zhou, Huacong
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p. 6944 - 6952
(2020/03/03)
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- Activation of Chiral (Salen)AlCl Complex by Phosphorane for Highly Enantioselective Cyanosilylation of Ketones and Enones
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Phosphoranes 2 are identified as a class of effective Lewis bases to activate chiral (salen)AlCl complex 1 to enhance its electrophilicity. Accordingly, a three-component catalyst system consisting of complex 1, phosphorane 2e, and Ph3PO is developed as a powerful tool for asymmetric ketone cyanosilylation. In particular, an unprecedented highly enantioselective cyanosilylation of linear aliphatic ketones is achieved. A tandem Wittig-cyanosilylation sequence starting from phosphorane 2a and enals 10 is further achieved, which internally utilizes the Ph3PO byproduct and remaining phosphorane 2a as cocatalysts for cyanosilylation of α,β,γ,δ-unsaturated enones, providing atom-efficient access to valuable chiral conjugated dienes and enynes. The high efficiency of the cyanosilylation originates from orthogonal activation of both (salen)AlCl complex 1 and cyanotrimethylsilane by the phosphorane and Ph3PO, respectively. This mechanistic insight is supported by NMR, MS, and ReactIR analyses and DFT calculations. Furthermore, the formation of charged complexes through the activation of chiral complex 1 by phosphorane 2a is confirmed by electrical conductivity experiments.
- Zeng, Xing-Ping,Cao, Zhong-Yan,Wang, Xin,Chen, Long,Zhou, Feng,Zhu, Feng,Wang, Cui-Hong,Zhou, Jian
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supporting information
p. 416 - 425
(2016/01/25)
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- Improved conditions for the proline-catalyzed aldol reaction of acetone with aliphatic aldehydes
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The proline-catalyzed asymmetric aldol reaction between aliphatic aldehydes and acetone has, to date, remained underdeveloped. Challenges in controlling this reaction include avoiding undesired side reactions such as aldol condensation and self-aldolization. In recent years we have developed optimized conditions, which enable high yields and good to excellent enantioselectivities, and which are presented in this communication. Georg Thieme Verlag Stuttgart New York.
- Martínez, Alberto,Zumbansen, Kristina,D?hring, Arno,Van Gemmeren, Manuel,List, Benjamin
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supporting information
p. 932 - 934
(2014/05/06)
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- Tetrabutylammonium peroxydisulfate in organic synthesis; IV. An efficient, highly selective and oxidative deoximation by tetrabutylammonium peroxydisulfate
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Tetrabutylammonium peroxydisulfate has been proved out to be an efficient and highly chemoselective reagent for the conversion of oximes to the corresponding carbonyl compounds under mild conditions.
- Chen, Fener,Liu, Anchang,Yan, Qiongjiao,Liu, Mingxing,Zhang, Daoming,Shao, Lanying
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p. 1049 - 1056
(2007/10/03)
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- Use of a Sacrificial Aluminum Anode in the Acylation of Some Olefins
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The acylation of some alicyclic and aliphatic alkenes by the electrochemical generation of a catalyst using a sacrificial aluminum anode was investigated. Substrates were electrolyzed in a dichloromethane solution of an appropriate electrolyte (tetraalkylammonium salts) in the presence of an acylating agent (acetyl chloride or anhydride). Thus, unsubstituted cycloalkenes, namely cyclohexene and cycloheptene, gave by that reaction conjugated ketones, i.e. the corresponding 1-acetylcycloalkenes, as the only unsaturated carbonyl compounds in moderate-to-good yields. Under the same reaction conditions their 1-methyl derivatives gave mixtures of the corresponding conjugated and β,γ-unsaturated isomeric ketones in which unconjugated compounds predominate. In both cases unsaturated ketones were accompanied by different amounts of side products. Terminal aliphatic alkenes (1-hexene, 1-heptene, and 1-dodecene) afforded only conjugated a ketone with a normal skeleton, but in lower yields. The acylation of cyclohexene was studied in more detail, altering the reaction conditions by changing the reaction temperature, the supporting electrolyte, the acylating agent and the electrochemical cell. Mechanistic considerations were made on the basis of the products distribution and some theoretical calculations being made by the MOPAC program package (version 7.0).
- Vukicevic, Rastko D.,Joksovic, Ljubinka,Konstantinovic, Stanimir,Markovic, Zoran,Mihailovic, Mihailo Lj.
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p. 899 - 904
(2007/10/03)
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- Selective hydrogenation of simple and functionalized conjugated dienes using a binuclear palladium complex catalyst precursor
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The selective 1,2-hydrogenation of simple and functionalized conjugated dienes is catalyzed by preactivation of the binuclear palladium complex, [(Bu(t)2PH)PdPBu(t)2]2 with oxygen, in THF at room temperature and 1 atm of hydrogen pressure, to form monoenes in excellent yield.
- Cho, In Sik,Alper, Howard
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p. 5673 - 5676
(2007/10/02)
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- A New Route to 5-Substituted Resorcinols and Related Systems
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Michael-type additions of phenylsulphinylacetate esters to αβ-unsaturated ketones produce cyclohexane-1,3-dione derivatives, which, after thermal elimination of benzenesulphenic acid, give the corresponding 5-substituted resorcinols, such as olivetol.The scope of this entry into other aromatic systems, such as 3,5-disubstituted and 2,3,5-trisubstituted phenols and orsellinic acid has been explored.
- Jaxa-Chamiec, Albert A.,Sammes, Peter G.,Kennewell, Peter D.
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p. 170 - 175
(2007/10/02)
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