- Direct Aerobic α-Hydroxylation of Arylacetates for the Synthesis of Mandelates
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Aerobic α-hydroxylation of α-methylene esters has proven challenging due to overoxidation and hydrolysis of the materials. In this article, KOtBu-promoted TBAB-catalyzed α-hydroxylation of α-methylene aryl esters using O2as the oxyge
- Xu, Changming,Li, Xiangfan,Bai, Lei
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p. 4298 - 4304
(2022/03/16)
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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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- Ester Formation via Symbiotic Activation Utilizing Trichloroacetimidate Electrophiles
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Trichloroacetimidates are useful reagents for the synthesis of esters under mild conditions that do not require an exogenous promoter. These conditions avoid the undesired decomposition of substrates with sensitive functional groups that are often observed with the use of strong Lewis or Br?nsted acids. With heating, these reactions have been extended to benzyl esters without electron-donating groups. These inexpensive and convenient methods should find application in the formation of esters in complex substrates.
- Mahajani, Nivedita S.,Meador, Rowan I. L.,Smith, Tomas J.,Canarelli, Sarah E.,Adhikari, Arijit A.,Shah, Jigisha P.,Russo, Christopher M.,Wallach, Daniel R.,Howard, Kyle T.,Millimaci, Alexandra M.,Chisholm, John D.
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p. 7871 - 7882
(2019/06/27)
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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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- Silica-supported HClO4 promotes catalytic solvent- and metal-free O-H insertion reactions with diazo compounds
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Solvent-free O-H insertion reactions in the presence of diazo carbonyl compounds were carried-out in very mild conditions. Unlike the traditional metal-catalysed version, employing rhodium acetate dimer, this method uses eco-friendly silica-supported HClO4 as the catalyst. Only 0.3 mol% of this Br?nsted acid catalyst, that can also be recycled several times, is necessary to guarantee very good yields (up to 97%) in the O-H insertion reactions. Reaction set-up is simple and permitted the preparation of forty-three α-hydroxy and α-alkoxy esters/ketones in just 1 h and at room temperature.
- Gallo, Rafael Douglas C.,Burtoloso, Antonio C. B.
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p. 4547 - 4556
(2018/10/17)
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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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- Chemoselective esterification of α-hydroxyacids catalyzed by salicylaldehyde through induced intramolecularity
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A new, direct and chemoselective esterification of α-hydroxyacids was developed using a reversible covalent-binding strategy. By taking advantage of acetal chemistry, simple aldehydes can be used to efficiently catalyze the esterification of α-hydroxy carboxylic acids in the presence of β-hydroxyacid moieties or other carboxylic acids in amounts equal to or in excess of the alcohols. A diverse array of α-aryl, α-alkyl, α-heteroaryl, and functionalized α-hydroxyacids were smoothly esterified with 1° and 2° alcohols catalyzed by 10 mol% inexpensive and commercially available salicylaldehyde, furnishing the resultant esterification products in 83-95% yields after a simple basic aqueous workup to remove the unreacted hydroxyacids. In addition, the salicylaldehyde can be recovered through vacuum distillation or silica gel purification, thereby meeting the standards of green chemistry. A mechanistic study proved that the formation of covalent adduct III during our proposed catalytic cycle (Scheme 1A) is responsible for the real catalysis.
- Weng, Shiue-Shien,Li, Hsin-Chun,Yang, Teng-Mao
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p. 1976 - 1986
(2013/03/13)
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- Selective reduction of aldehydes and ketones to alcohols with ammonia borane in neat water
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Chemoselective reduction of various carbonyl compounds to alcohols with ammonia borane (AB), a nontoxic, environmentally benign, and easily handled reagent, in neat water was achieved in quantitative conversions and high isolated yields. Interestingly, α- and β-keto esters were selectively reduced to corresponding hydroxyl esters by AB, while diols were obtained when sodium borohydride was used as a reducing agent. The procedure is also compatible with the presence of a variety of base-labile protecting groups, such as tosyl, acetyl, benzoyl, ester groups, and acid-labile protecting groups such as trityl and TBDMS groups, and others, such as the unsaturated double bond, nitro and cyano groups. Finally, a kilo scale reaction of methyl benzoylformate with AB was conducted in water and gave methyl mandelate in 94% yield.
- Shi, Lei,Liu, Yingying,Liu, Qingfeng,Wei, Bin,Zhang, Guisheng
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experimental part
p. 1372 - 1375
(2012/06/04)
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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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- Direct atom-efficient esterification between carboxylic acids and alcohols catalyzed by amphoteric, water-tolerant TiO(acac)2
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A diverse array of oxometallic species were examined as catalysts for a test direct condensation of benzoic acid and 2-phenylethanol in 1:1 stoichiometry. Besides group IVB MOCl2-XH2O and TiOX 2-xH2O, group VB VOCl2-xTHF and group IVB TiO(acac)2 were found to be the most efficient and water-tolerant catalysts for the test reaction. The new neutral catalytic protocol with the optimal TiO(acac)2 tolerates many stereo/electronic structural variations in both (di)-acid (1°-3° alkyl and aryl) and (di)alcohol (1°, 2° alkyl, and aryl) components with high chemoselectivity.
- Chen, Chien-Tien,Munot, Yogesh S.
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p. 8625 - 8627
(2007/10/03)
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- An efficient and convenient procedure for preparation of mandelates catalysed by TiO2/SO4/2- solid superacid
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An easy and efficient synthesis of mandelates in excellent yields from mandelic acid with alcohols catalysed by TiO2/SO42- solid superacid.
- Jin,Ma,Li,Sun,Li
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p. 2051 - 2054
(2007/10/03)
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- Fe2(SO4)3 · xH2O in synthesis: A new and convenient catalyst for the esterification of mandelic acid with alcohols
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Treatment of various of alcohols with mandelic acid in the presence of a catalytic amount of Fe2(SO4)3 · xH2O to give the corresponding esters in good yields.
- Zhang, Gui-Sheng,Gong, Hui
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p. 1547 - 1551
(2007/10/03)
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- A general and simple synthesis of phenylglyoxylic esters via the oxidation of mandelic esters with ammonium chlorochromate adsorbed on alumina
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A general method for preparation of phenylglyoxylic esters by oxidation of mandelic esters with readily available ammonium chlorochromate adsorbed on alumina is described.
- Zhang, Gui-Sheng,Gong, Hui
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p. 3149 - 3153
(2007/10/03)
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- A CONVENIENT METHOD FOR ENZYMATIC BENZYL-ALKYL TRANSESTERIFICATION UNDER MILD NEUTRAL CONDITIONS
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Lipases from Candida cylindracea and from Pseudomonas fluorescens efficiently catalyse the benzyl to alkyl transesterification in organic solvents under mild conditions in nearly quantitative yields.
- Gutman, Arie L.,Shkolnik, Eleonora,Shapira, Michal
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p. 8775 - 8780
(2007/10/02)
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- Certain optically active mono esters of dicarboxylic acids
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Optically active mono-esters of dicarboxylic acid of the formula III: STR1 being useful as intermediates for preparing optically active natural products or medicines; asymmetric synthesis process for preparing thereof being characterized by the reaction of an acid anhydride with an (R)- or (S)-arylacetic acid derivative; and the key substances therefor are also claimed.
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- Synthetic cephalotaxine esters having antileukemic activity
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Six acyl esters of cephalotaxine have been synthesized by ordinary and standard procedures, and all have demonstrated chemotherapeutic activity against leukemia in animals.
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