- Hydrogen-bond-assisted transition-metal-free catalytic transformation of amides to esters
-
The amide C-N cleavage has drawn a broad interest in synthetic chemistry, biological process and pharmaceutical industry. Transition-metal, luxury ligand or excess base were always vital to the transformation. Here, we developed a transition-metal-free hydrogen-bond-assisted esterification of amides with only catalytic amount of base. The proposed crucial role of hydrogen bonding for assisting esterification was supported by control experiments, density functional theory (DFT) calculations and kinetic studies. Besides broad substrate scopes and excellent functional groups tolerance, this base-catalyzed protocol complements the conventional transition-metal-catalyzed esterification of amides and provides a new pathway to catalytic cleavage of amide C-N bonds for organic synthesis and pharmaceutical industry. [Figure not available: see fulltext.]
- Huang, Changyu,Li, Jinpeng,Wang, Jiaquan,Zheng, Qingshu,Li, Zhenhua,Tu, Tao
-
-
- Direct Amidation of Esters by Ball Milling**
-
The direct mechanochemical amidation of esters by ball milling is described. The operationally simple procedure requires an ester, an amine, and substoichiometric KOtBu and was used to prepare a large and diverse library of 78 amide structures with modest to excellent efficiency. Heteroaromatic and heterocyclic components are specifically shown to be amenable to this mechanochemical protocol. This direct synthesis platform has been applied to the synthesis of active pharmaceutical ingredients (APIs) and agrochemicals as well as the gram-scale synthesis of an active pharmaceutical, all in the absence of a reaction solvent.
- Barreteau, Fabien,Battilocchio, Claudio,Browne, Duncan L.,Godineau, Edouard,Leitch, Jamie A.,Nicholson, William I.,Payne, Riley,Priestley, Ian
-
supporting information
p. 21868 - 21874
(2021/09/02)
-
- Nickel-Catalyzed Photodehalogenation of Aryl Bromides
-
Herein, we describe a Ni-catalyzed photodehalogenation of aryl bromides under visible-light irradiation that utilizes tetrahydrofuran as hydrogen source. The protocol obviates the need for exogeneous amine reductants or photocatalysts and is characterized by its simplicity and broad scope, including challenging substrate combinations.
- Higginson, Bradley,Sanjosé-Orduna, Jesus,Gu, Yiting,Martin, Ruben
-
supporting information
p. 1633 - 1636
(2021/04/23)
-
- Photochemical Activation of Aromatic Aldehydes: Synthesis of Amides, Hydroxamic Acids and Esters
-
A cheap, facile and metal-free photochemical protocol for the activation of aromatic aldehydes has been developed. Utilizing thioxanthen-9-one as the photocatalyst and cheap household lamps as the light source, a variety of aromatic aldehydes have been activated and subsequently converted in a one-pot reaction into amides, hydroxamic acids and esters in good to high yields. The applicability of this method was highlighted in the synthesis of Moclobemide, a drug against depression and social anxiety. Extended and detailed mechanistic studies have been conducted, in order to determine a plausible mechanism for the reaction.
- Nikitas, Nikolaos F.,Apostolopoulou, Mary K.,Skolia, Elpida,Tsoukaki, Anna,Kokotos, Christoforos G.
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p. 7915 - 7922
(2021/05/03)
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- Tropolonate salts as acyl-transfer catalysts under thermal and photochemical conditions: Reaction scope and mechanistic insights
-
Acyl-transfer catalysis is a frequently used tool to promote the formation of carboxylic acid derivatives, which are important synthetic precursors and target compounds in organic synthesis. However, there have been only a few structural motifs known to efficiently catalyze the acyl-transfer reaction. Herein, we introduce a different acyl-transfer catalytic paradigm based on the tropolone framework. We show that tropolonate salts, due to their strong nucleophilicity and photochemical activity, can promote the coupling reaction between alcohols and carboxylic acid anhydrides or chlorides to give products under thermal or blue light photochemical conditions. Kinetic studies and density functional theory calculations suggest interesting mechanistic insights for reactions promoted by this acyl-transfer catalytic system.
- Mai, Binh Khanh,Koenigs, Rene M.,Nguyen, Thanh Vinh,Lyons, Demelza J.M.,Empel, Claire,Pace, Domenic P.,Dinh, An H.
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p. 12596 - 12606
(2020/11/18)
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- Chemoselective Tertiary C?H Hydroxylation for Late-Stage Functionalization with Mn(PDP)/Chloroacetic Acid Catalysis
-
Aromatic and heterocyclic functionality are ubiquitous in pharmaceuticals. Herein, we disclose a new Mn(PDP) catalyst system using chloroacetic acid additive capable of chemoselectively oxidizing remote tertiary C(sp3)?H bonds in the presence of a broad range of aromatic and heterocyclic moieties. Although catalyst loadings can be lowered to 0.1 mol% under a Mn(PDP)/acetic acid system for aromatic and non-basic nitrogen heterocycle substrates, the Mn(PDP)/chloroacetic acid system generally affords 10–15% higher isolated yields on these substrates and is uniquely effective for remote C(sp3)?H hydroxylations in substrates housing basic nitrogen heterocycles. The demonstrated ability to perform Mn(PDP)/chloroacetic acid C(sp3)?H oxidations in pharmaceutically relevant complex molecules on multi-gram scales will facilitate drug discovery processes via late-stage functionalization. (Figure presented.).
- Chambers, Rachel K.,Zhao, Jinpeng,Delaney, Connor P.,White, M. Christina
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supporting information
p. 417 - 423
(2019/12/27)
-
- Base-catalyzed selective esterification of alcohols with unactivated esters
-
A practical and efficient base-catalyzed esterification has been developed for the facile synthesis of a broad range of esters from simple alcohols with unactivated tert-butyl esters. This protocol could be conducted at mild conditions, providing esters in high to excellent yields with good functional tolerance. Mechanistic studies provided evidence of an exchange of the tert-butyl alkoxide metal with the alcohol, producing a new alkoxide to participate in the transesterification reaction.
- Zhang, Chunyan,Zhang, Guoying,Luo, Shizhong,Wang, Chunfu,Li, Huiping
-
supporting information
p. 8467 - 8471
(2018/12/01)
-
- Fluoride-Catalyzed Esterification of Amides
-
In recent years, it has been demonstrated that amide carbon–nitrogen bonds can be activated and selectively cleaved using transition metal catalysts. However, these methodologies have been restricted to specific amides; a one-to-one relationship exists between the catalytic system and the amides and also uses large amounts of transition-metal catalysts and ligands. Hence, we now report a general strategy for esterification of common amides using fluoride as a catalyst. This method shows high functional group tolerance, and notably it requires only a slight excess of the alcohol nucleophile, which is a rare case in transition-metal-free amide transformations. Moreover, this approach may provide a new understanding for further studies on esterification of amides and is expected to stimulate the development of alternative methods for direct functionalization of amides.
- Wu, Hongxiang,Guo, Weijie,Daniel, Stelck,Li, Yue,Liu, Chao,Zeng, Zhuo
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p. 3444 - 3447
(2018/02/21)
-
- Epimerization of Tertiary Carbon Centers via Reversible Radical Cleavage of Unactivated C(sp3)-H Bonds
-
Reversible cleavage of C(sp3)-H bonds can enable racemization or epimerization, offering a valuable tool to edit the stereochemistry of organic compounds. While epimerization reactions operating via cleavage of acidic C(sp3)-H bonds, such as the Cα-H of carbonyl compounds, have been widely used in organic synthesis and enzyme-catalyzed biosynthesis, epimerization of tertiary carbons bearing a nonacidic C(sp3)-H bond is much more challenging with few practical methods available. Herein, we report the first synthetically useful protocol for the epimerization of tertiary carbons via reversible radical cleavage of unactivated C(sp3)-H bonds with hypervalent iodine reagent benziodoxole azide and H2O under mild conditions. These reactions exhibit excellent reactivity and selectivity for unactivated 3° C-H bonds of various cycloalkanes and offer a powerful strategy for editing the stereochemical configurations of carbon scaffolds intractable to conventional methods. Mechanistic study suggests that the unique ability of N3? to serve as a catalytic H atom shuttle is critical to reversibly break and reform 3° C-H bonds with high efficiency and selectivity.
- Wang, Yaxin,Hu, Xiafei,Morales-Rivera, Cristian A.,Li, Guo-Xing,Huang, Xin,He, Gang,Liu, Peng,Chen, Gong
-
supporting information
p. 9678 - 9684
(2018/07/21)
-
- Visible-Light Photocatalysis Employing Dye-Sensitized Semiconductor: Selective Aerobic Oxidation of Benzyl Ethers
-
The aerobic oxidation is an attractive approach toward environmentally benign synthesis of fine chemicals. In addition, dye-sensitized semiconductors are underdeveloped photocatalysts for selective organic synthesis. With the aid of catalytic eosin Y-sensitized titanium dioxide, we have developed efficient aerobic photooxidation of benzyl ethers to benzoates, featuring low cost, high atom economy, broad substrate scope, and user-friendly setup. Furthermore, preliminary mechanistic studies established that the reaction pathway likely entails a photoinduced, radical-based two-step process via an isolable peroxide intermediate.
- Ren, Li,Yang, Ming-Meng,Tung, Chen-Ho,Wu, Li-Zhu,Cong, Huan
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p. 8134 - 8138
(2017/12/08)
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- Kinetic Modeling of the Nickel-Catalyzed Esterification of Amides
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Nickel-catalyzed coupling reactions provide exciting tools in chemical synthesis. However, most methodologies in this area require high catalyst loadings, which commonly range from 10-20 mol % nickel. Through an academic-industrial collaboration, we demonstrate that kinetic modeling can be used strategically to overcome this problem, specifically within the context of the Ni-catalyzed conversion of amides to esters. The successful application of this methodology to a multigram-scale coupling, using only 0.4 mol % Ni, highlights the impact of this endeavor.
- Weires, Nicholas A.,Caspi, Daniel D.,Garg, Neil K.
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p. 4381 - 4385
(2017/07/24)
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- A synthetic process of L-menthol
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The invention relates to the field of spice synthesis and particularly relates to a synthetic process of L-menthol. The process includes steps of d,l-menthol synthesizing, d,l-menthol rectification, d,l-menthol esterification, d,l-menthyl benzoate rectification, d,l-menthyl benzoate resolution, D-menthol synthesizing, menthol isomerization and L-menthol synthesizing. The process adopts thymol that is a simple, easily available and cheap chemical product as a raw material. Esterification conditions are optimized and the esterification and rectification are performed at the same time so as to allow the esterification to be converted into a way beneficial to d,l-menthyl benzoate production, thus increasing the esterification yield. Crystallization and resolution are optimized by utilization of the d,l-menthyl benzoate. Preparation of the L-menthol by the process is characterized by being high in yield, low in cost, simple and convenient in operation, suitable for continuous and large-scale production, and the like. According to the process, operation of the process is cyclic with a whole system being sealed, and the process is free of waste water, energy-saving and environmental friendly.
- -
-
-
- Benchtop Delivery of Ni(cod)2 using Paraffin Capsules
-
A facile method that allows for Ni(cod)2 to be used on the benchtop is reported. The procedure involves the preparation of paraffin-Ni(cod)2 capsules, which are stable to air and moisture. It is demonstrated that these readily available capsules can be used to promote a range of Ni(cod)2-catalyzed transformations. These studies are expected to promote the further use of Ni(cod)2 in organic synthesis.
- Dander, Jacob E.,Weires, Nicholas A.,Garg, Neil K.
-
supporting information
p. 3934 - 3936
(2016/08/16)
-
- ZINC COMPLEX
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A zinc complex characterized in exhibiting an octahedral structure and being configured from repeating units represented by general formula (I): wherein L represents a linker region, and R1 represents a C1-4 alkyl group, which can have a halogen atom.
- -
-
Paragraph 0190-
(2016/05/19)
-
- Sulfination of Alcohols with p-Toluenesulfonylmethyl Isocyanide under Metal-Free Conditions: A Mitsunobu Approach
-
A Mitsunobu approach for the synthesis of sulfinate esters by direct nucleophilic substitution of alcohols is described. The salient features of this strategy include neutral and metal-free conditions for the rapid synthesis of sulfinates in high yields. The present protocol using p-toluenesulfonylmethyl isocyanide (TosMIC) and the triphenylphosphine (TPP)/diisopropyl azodicarboxylate (DIAD) reagent system represents the general synthetic route to this important class of compounds. (Figure presented.).
- Kadari, Lingaswamy,Radha Krishna, Palakodety,Lakshmi Prapurna
-
supporting information
p. 3863 - 3868
(2016/12/16)
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- Conversion of amides to esters by the nickel-catalysed activation of amide C-N bonds
-
Amides are common functional groups that have been studied for more than a century. They are the key building blocks of proteins and are present in a broad range of other natural and synthetic compounds. Amides are known to be poor electrophiles, which is typically attributed to the resonance stability of the amide bond. Although amides can readily be cleaved by enzymes such as proteases, it is difficult to selectively break the carbon-nitrogen bond of an amide using synthetic chemistry. Here we demonstrate that amide carbon-nitrogen bonds can be activated and cleaved using nickel catalysts. We use this methodology to convert amides to esters, which is a challenging and underdeveloped transformation. The reaction methodology proceeds under exceptionally mild reaction conditions, and avoids the use of a large excess of an alcohol nucleophile. Density functional theory calculations provide insight into the thermodynamics and catalytic cycle of the amide-to-ester transformation. Our results provide a way to harness amide functional groups as synthetic building blocks and are expected to lead to the further use of amides in the construction of carbon-heteroatom or carbon-carbon bonds using non-precious-metal catalysis.
- Hie, Liana,Fine Nathel, Noah F.,Shah, Tejas K.,Baker, Emma L.,Hong, Xin,Yang, Yun-Fang,Liu, Peng,Houk,Garg, Neil K.
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-
- Modified Yamaguchi reagent: Convenient and efficient esterification
-
A convenient and efficient esterification method that used a modified Yamaguchi reagent (2,4,6-trichlorobenzoyl chloride-4-dimethylaminopyridine) and avoided use not only of intractable acid chloride but also of acid anhydrides was proposed. The reaction mechanism was described by Fourier transform infrared spectroscopy and supported by a density functional theory calculation.
- Okuno, Yoshinori,Isomura, Shigeki,Nishibayashi, Akihiro,Hosoi, Aiko,Fukuyama, Kei,Ohba, Masashi,Takeda, Kazuyoshi
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supporting information
p. 2854 - 2860
(2014/10/15)
-
- 4-(N,N -dimethylamino)pyridine hydrochloride as a recyclable catalyst for acylation of inert alcohols: Substrate scope and reaction mechanism
-
4-(N,N-Dimethylamino)pyridine hydrochloride (DMAP·HCl), a DMAP salt with the simplest structure, was used as a recyclable catalyst for the acylation of inert alcohols and phenols under base-free conditions. The reaction mechanism was investigated in detail for the first time; DMAP·HCl and the acylating reagent directly formed N-acyl-4-(N′,N′-dimethylamino) pyridine chloride, which was attacked by the nucleophilic substrate to form a transient intermediate that released the acylation product and regenerated the DMAP·HCl catalyst.
- Liu, Zhihui,Ma, Qiaoqiao,Liu, Yuxiu,Wang, Qingmin
-
supporting information
p. 236 - 239
(2014/01/23)
-
- Heterobimetallic dinuclear lanthanide alkoxide complexes as acid-base difunctional catalysts for transesterification
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A practical lanthanide(III)-catalyzed transesterification of carboxylic esters, weakly reactive carbonates, and much less-reactive ethyl silicate with primary and secondary alcohols was developed. Heterobimetallic dinuclear lanthanide alkoxide complexes [Ln2Na8{(OCH2CH2NMe2)}12(OH)2] (Ln = Nd (I), Sm (II), and Yb (III)) were used as highly active catalysts for this reaction. The mild reaction conditions enabled the transesterification of various substrates to proceed in good to high yield. Efficient activation of transesterification may be endowed by the above complexes as cooperative acid-base difunctional catalysts, which is proposed to be responsible for the higher reactivity in comparison with simple acid/base catalysts.
- Zeng, Ruijie,Sheng, Hongting,Zhang, Yongcang,Feng, Yan,Chen, Zhi,Wang, Junfeng,Chen, Man,Zhu, Manzhou,Guo, Qingxiang
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p. 9246 - 9252
(2014/12/11)
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- Palladium-catalyzed fluorocarbonylation using N-formylsaccharin as CO source: General access to carboxylic acid derivatives
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N-Formylsaccharin, an easily accessible crystalline compound, has been employed as an efficient CO source in Pd-catalyzed fluorocarbonylation of aryl halides to afford the corresponding acyl fluorides in high yields. The reactions use a near-stoichiometric amount of the CO source (1.2 equiv) and tolerate diverse functional groups. The acyl fluorides obtained could be readily transformed into various carboxylic acid derivatives such as carboxylic acid, esters, thioesters, and amides in a one-pot procedure.
- Ueda, Tsuyoshi,Konishi, Hideyuki,Manabe, Kei
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p. 5370 - 5373
(2013/11/06)
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- Benzoyl peroxide-imidazole: A novel and efficient reagent for the mild conversion of alcohols or phenols into benzoates
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A very mild, one-pot, and expedient protocol for the conversion of alcohols and phenols into their corresponding benzoates using imidazole and benzoyl peroxide as a novel reagent is described.
- Nowrouzi, Najmeh,Alizadeh, Seyedeh Zahra
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p. 2412 - 2414
(2013/06/26)
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- Direct esterification of carboxylic acids with alcohols catalyzed by Iron(III) acetylacetonate complex
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Direct condensation of carboxylic acids and alcohols with electronic, steric, and functional group variations was carried out using the environmentally benign, moisture-stable, inexpensive, and recoverable iron(III) acetylacetonate [Fe(acac)3] as catalyst (5 mol%). This iron salt efficiently catalyzed the esterification of several primary and secondary alcohols in refluxing xylene, without the need for a dehydration reagent. The chemoselectivity of the proposed protocol was demonstrated by the selective esterification of primary alcohol functionality in racemic 1-phenylethane-1,2- diol with benzoic acid. The esterification was also applicable to unmasked α-hydroxyacid, guasiaromatic, heterocyclic, and N-protected amino acids. Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications to view the free supplemental file.
- Weng, Shiue-Shien,Chen, Fong-Kuang,Ke, Chih-Shueh
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p. 2615 - 2621
(2013/07/26)
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- The phosphate-carboxylate mixed-anhydride method: A mild, efficient process for ester and amide bond construction
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A highly efficient carboxylate-phosphate anhydride pathway is described for the direct, economical synthesis of esters and amides from carboxylic acids and alcohols or amines. The reaction proceeds with retention of configuration with both chiral secondary alcohols and α-amino acid derivatives allowing access to useful chiral auxiliaries, ligands, and organocatalysts. Ester and amide products can be isolated directly in high yield due to the water soluble nature of the side products.
- McNulty, James,Vemula, Ramesh,Krishnamoorthy, Venkatesan,Robertson, Al
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experimental part
p. 5415 - 5421
(2012/09/08)
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- Synthesis, antimicrobial evaluation, and QSAR analysis of 2-isopropyl-5-methylcyclohexanol derivatives
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A series of 2-isopropyl-5-methylcyclohexanol derivatives were synthesized and evaluated for their antibacterial activity against Gram-positive Staphylococcus aureus and Bacillus subtilis and Gram-negative Escherichia coli and in vitro antifungal activity against Candida albicans and Aspergillus niger. The results of antimicrobial activity demonstrated that the compounds 10, 20, and 21 were the most active ones among the synthesized compounds. The QSAR studies revealed the importance of dipole moment (μ), total energy (Te), and topological parameters (κ1 and κ3) in describing the antimicrobial activity of 2-isopropyl-5-methylcyclohexanol derivatives. Springer Science+Business Media, LLC 2011.
- Singh, Manjeet,Kumar, Sunil,Kumar, Ashwani,Kumar, Pradeep,Narasimhan, Balasubramanian
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p. 511 - 522
(2012/08/07)
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- An effective method to introduce carbon acid functionality: 2,2-bis(trifluoromethanesulfonyl)ethylation reaction of arenes
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Introducing strong acids: The reaction of electron-rich arenes with Tf 2CHCH2CHTf2 (Tf=trifluoromethanesulfonyl; triflyl) smoothly gave 2,2-bis(triflyl)ethylated arenes. This reaction provides a convenient methodology for the introduction of a Tf2CH group, which is known to be a strongly Bronsted acidic functionality, to organic compounds in a regioselective manner (see scheme). On the basis of this reaction, significantly active and thermally stable carbon acid catalysts were developed.
- Yanai, Hikaru,Ogura, Hiroshi,Fukaya, Haruhiko,Kotani, Akira,Kusu, Fumiyo,Taguchi, Takeo
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supporting information; experimental part
p. 11747 - 11751
(2011/11/06)
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- Ligand-assisted rate acceleration in lanthanum
-
The transesterification of an equimolar mixture of carboxylic esters and primary (1°), secondary (2°), and tertiary (3°) alcohols in hydrocarbon solvents was promoted with high efficiency by a lanthanum(III) complex, which was prepared in situ from lanthanum (III) isopropoxide (1 mol %) and 2-(2-methoxyethoxy)ethanol (2 mol %). The present La(III) catalyst was highly effective for the chemoselective transesterification in the presence of competitive 1°-and 2°-amines. Remarkably, esters were obtained in good to excellent yields as colorless materials without an inconvenient workup procedure.
- Hatano, Manabu,Furuya, Yoshiro,Shimmura, Takumi,Moriyama, Katsuhiko,Kamiya, Sho,Maki, Toshikatsu,Ishihara, Kazuaki
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supporting information; experimental part
p. 426 - 429
(2011/04/15)
-
- Transesterification catalyzed by iron(III) β-diketonate species
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A practical and clean protocol for transesterification catalyzed by a 5 mol % cheap, non-toxic and moisture stable Fe(acac)3 or other iron(III) β-diketonate species in solvent, such as heptane under azeotropic condition is developed. A remarkable rate enhancement was observed upon the addition of 5 mol % of an inorganic base, such as Na2CO3, which suggests that faster formation of a dimeric μ-alkoxy-bridged iron(III) species under alkaline conditions facilitates catalytic turnover. This system provides smooth transesterification over a wide range of structurally diverse esters and alcohols without disturbing functional groups. In addition, the use of iron β-diketonate complexes as catalysts is more environmentally friendly, safer, and economical than other transition-metal catalysts. Preliminary mechanistic studies indicate that the active catalyst is likely a dimeric μ-alkoxy-bridged iron(III) species, as determined by X-ray crystallography of [Fe(dbm)2(O-n-Bu)]2 derived from the alcoholysis of Fe(dbm)3 under alkaline conditions.
- Weng, Shiue-Shien,Ke, Chih-Shueh,Chen, Fong-Kuang,Lyu, You-Fu,Lin, Guan-Ying
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experimental part
p. 1640 - 1648
(2011/04/17)
-
- Inversion of secondary chiral alcohols in toluene with the tunable complex of R3N{single bond}R′COOH
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The SN2 reaction of enantiomerically pure sulfonates with the tunable complex of R3N-R′COOH in toluene has been extensively studied. It was revealed that the molar ratio of the tertiary amines and carboxylic acids in the complex of R3NR′COOH is crucial for the SN2 reaction, and should be tuned for each sulfonate to give the best yield. Fifteen sulfonates 1 and 3-13 (Scheme 2) were prepared and transformed into 22 corresponding inverted esters 2 and 14-24 (Scheme 2) in good to high yields.
- Shi, Xiao-Xin,Shen, Chun-Li,Yao, Jian-Zhong,Nie, Liang-Deng,Quan, Na
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experimental part
p. 277 - 284
(2010/05/18)
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- Enzymatic production of l-menthol by a high substrate concentration tolerable esterase from newly isolated Bacillus subtilis ECU0554
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Enzymatic preparation of l-menthol has been attracting much attention in the flavor and fragrance industry. A new ideal strain, Bacillus subtilis ECU0554, which exhibited high hydrolytic activity and excellent enantioselectivity towards l-menthyl ester, has been successfully isolated from soil samples through enrichment culture and identified as Bacillus subtilis by 16S rDNA gene sequencing. The esterase extracted from B. subtilis ECU0554 (BSE) showed the best catalytic properties (E > 200) for dl-menthyl acetate among the five menthyl esters examined. Enantioselective hydrolysis of 100 mM dl-menthyl acetate at 30°C and pH 7.0, using crude BSE as biocatalyst and 10% ethanol (v/v) as cosolvent, resulted in 49.0% conversion (3 h) and 98.0% ee for the l-menthol produced, which were much better than those using commercial enzymes tested. Moreover, BSE exhibited strong tolerance against high substrate concentration (up to 500 mM), and the concentration of l-menthol produced could reach as high as 182 mM, and more importantly, the optical purity of l-menthol produced was kept above 97% ee, which were not found in previous reports. These results imply that BSE is a potentially promising bio-catalyst for the large-scale enzymatic preparation of l-menthol. Using this excellent biocatalyst, the enzymatic production of l-menthol will become a mild, efficient, inexpensive and easy-to-use "green chemistry" methodology.
- Zheng, Gao-Wei,Yu, Hui-Lei,Zhang, Jian-Dong,Xu, Jian-He
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experimental part
p. 405 - 414
(2009/11/30)
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- Easily prepared azopyridines as potent and recyclable reagents for facile esterification reactions. An efficient modified mitsunobu reaction
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(Chemical Equation Presented) The 2,2′-, 3,3′-, and 4,4′-azopyridines (azpy) and their alkyl pyridinium ionic liquids were studied as a new class of electron-deficient reagents for Mitsunobu esterification reactions. Among these compounds, 4,4′-azopyridine was found to be the most suitable one for esterification and thioesterification reactions. This new reagent promises to provide general and complementary solutions for separation problems in Mitsunobu reactions without restricting the reaction scope and facilitates the isolation of its hydrazine byproduct. The pyridine hydrazine byproduct can be simply recycled to its azopyridine by an oxidation reaction.
- Iranpoor, Nasser,Firouzabadi, Habib,Khalili, Dariush,Motevalli, Somayeh
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p. 4882 - 4887
(2008/09/21)
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- Magnesium bistrifluoromethanesulfonimide as a new and efficient acylation catalyst
-
Magnesium bistrifluoromethanesulfonimide catalyzed the acetylation of phenols, alcohols, and thiols under solvent-free conditions at room temperature and in short times. Electron-deficient and sterically hindered phenols provided excellent yields. The catalyst was found to be general for acylation with other anhydrides, such as propionic, isobutyric, pivalic, chloroacetic, and benzoic anhydrides. The rate of acylation was influenced by the electronic and steric factors associated with the anhydride. The reaction with less electrophilic anhydrides (e.g., chloroacetic and benzoic anhydrides) required higher temperature (~80 °C). Chemoselective acetylation, pivalation, and benzoylation took place with acid-sensitive alcohols without any competitive dehydration/rearrangement.
- Chakraborti, Asit K.,Shivani
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p. 5785 - 5788
(2007/10/03)
-
- Dimethylmalonyltrialkylphosphoranes: Probing the steric effect on phosphorus and its stereochemical consequence in esterification reactions of chiral secondary alcohols
-
High chemical yields and high levels of stereochemical inversion are demonstrated in the phosphorane-mediated esterification reaction of chiral alcohols with non-hindered carboxylic acids through the incorporation of sterically non-hindered alkyl groups o
- Dyck,Zavorine,Robertson,Capretta,Larichev,Britten,McNulty
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p. 2548 - 2552
(2007/10/03)
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- Zinc oxide (ZnO) as a new, highly efficient, and reusable catalyst for acylation of alcohols, phenols and amines under solvent free conditions
-
Zinc oxide (ZnO) is a highly efficient catalyst for the acylation of a variety of alcohols, phenols and amines with acid chlorides or acid anhydrides under solvent free conditions. Primary, secondary, tertiary, allylic and benzylic alcohols, diols and phenols with electron donating or withdrawing substituents can be easily acylated in good to excellent yield.
- Hosseini Sarvari, Mona,Sharghi, Hashem
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p. 10903 - 10907
(2007/10/03)
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- Erbium(III) triflate as an extremely active acylation catalyst
-
Erbium(III) triflate is a powerful catalyst for the acylation of alcohols and phenols. The reaction works well for a large variety of simple and functionalized substrates by using different kinds of acidic anhydrides {Ac 2O, (EtCO)2O, [(CH3)3CO] 2O, Bz2O, and (CF3CO)2O} without isomerisation of chiral centres. Moreover, the catalyst can be easily recycled and reused without significant loss of activity.
- Procopio, Antonio,Dalpozzo, Renato,De Nino, Antonio,Maiuolo, Loredana,Russo, Beatrice,Sindona, Giovanni
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p. 1465 - 1470
(2007/10/03)
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- Process for the preparation of L-menthol
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L-Menthol is prepared from D,L-menthyl derivatives by enantioselective enzymatic cleavage.
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-
- Electrostatic catalysis by ionic aggregates: Scope and limitations of Mg(ClO4)2 as acylation catalyst
-
Alkali and alkaline earth metal perchlorates exhibit electrostatic catalysis in the activation of anhydrides for the acylation reaction. Perchlorates with higher values of the charge-size function of the metal ion exhibit better catalytic activity following the order Mg(ClO4) 2>Ba(ClO4)2>LiClO4. Acylation of structurally diverse phenols, thiols, alcohols, and amines have been carried out with stoichiometric amounts of anhydride at room temperature under solvent free conditions in the presence of catalytic amount of Mg(ClO4) 2. Sterically hindered and electron deficient phenols are efficiently acylated. Acylation with sterically hindered anhydrides such as iso-butyric, pivalic, and benzoic anhydrides are carried out with phenols and alcohols in excellent yields. Acid-sensitive alcohols are acylated in excellent yields without any competitive side reactions.
- Chakraborti, Asit K.,Sharma, Lalima,Gulhane, Rajesh,Shivani
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p. 7661 - 7668
(2007/10/03)
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- Efficient method for the preparation of carboxylic acid alkyl esters or alkyl phenyl ethers by a new-type of oxidation-reduction condensation using 2,6-dimethyl-1,4-benzoquinone and alkoxydiphenylphosphines
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A new-type of oxidation-reduction condensation proceeded smoothly to afford carboxylic acid alkyl esters or alkyl phenyl ethers in good to high yields by combined use of alkoxydiphenylphosphines (1) having primary, bulky secondary or tertiary alkoxy groups, a mild quinone-type oxidant such as 2,6-dimethyl-1,4-benzoquinone (DMBQ) and carboxylic acids or phenols. Generally, alkoxydiphenylphosphines were prepared easily from chlorodiphenylphosphine (2) and alcohols in the presence of pyridine, and were isolated by distillation. On the other hand, the phosphines 1 were also prepared in situ from N,N-dimethylaminodiphenylphosphine (3a) and primary or secondary alcohols while primary, bulky secondary or tertiary alkoxydiphenylphosphines were alternatively formed in situ by adding 2 to the "BuLi-treated alcohols in order to perform the above reactions by a one-pot procedure from alcohols and nucleophiles. The reaction of thus formed 1, DMBQ and carboxylic acids or phenols afforded the corresponding alkylated products, including hindered secondary and tertiary alkylated ones, in good to high yields at room temperature. In the case of using chiral secondary alcohols, the corresponding carboxylic acid alkyl esters were obtained as well in high yields with perfect inversion of stereochemistry by SN2 replacement.
- Shintou, Taichi,Kikuchi, Wataru,Mukaiyama, Teruaki
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p. 1645 - 1667
(2007/10/03)
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- Dimethylmalonyltrialkylphosphoranes: New general reagents for esterification reactions allowing controlled inversion or retention of configuration on chiral alcohols
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A new class of trialkylphosphorane has been prepared through reaction of a trialkylphosphine with 2-chlorodimethylmalonate in the presence of triethylamine. These new reagents promote the condensation reaction of carboxylic acids with alcohols to provide esters along with trialkylphosphine oxide and dimethylmalonate. The condensation reaction of chiral secondary alcohols can be controlled to give either high levels of inversion or retention through a subtle interplay involving basicity of the reaction media, solvent, and tuning the electronic and steric nature of the carboxylic acid and steric nature of the phosphorane employed. A coherent mechanism is postulated to explain these observations involving reaction via an initial acyloxyphosphonium ion.
- McNulty, James,Capretta, Alfredo,Laritchev, Vladimir,Dyck, Jeff,Robertson, Al J.
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p. 1597 - 1600
(2007/10/03)
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- High-Load, ROMP-Generated Oligomeric Bis-acid Chlorides: Design of Soluble and Insoluble Nucleophile Scavengers
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(Equation presented) An efficient strategy for scavenging a host of nucleophiles utilizing an oligomeric bis-acid chloride (OBAC), generated from the ROM polymerization of trans-bicyclo[2.2.1]hept-5-ene-2,3-dicarbonyl dichloride, is described. The reactivity and high load of the OBAC reagent is exploited in the scavenging of amines, alcohols, and thiols that are present in excess following a common benzoylation event. Following the scavenging event, these oligomers can be precipitated with EtOAc and filtered (SiO2), leaving benzoylated nucleophiles in excellent yield and purity.
- Moore, Joel D.,Byrne, Robert J.,Vedantham, Punitha,Flynn, Daniel L.,Hanson, Paul R.
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p. 4241 - 4244
(2007/10/03)
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- One-pot preparation of esters from carboxylic acids using the PPh3-CCl3CN system
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A convenient one-pot process for preparing various esters from carboxylic acids using the Ph3P-CCl3CN has been developed. Racemic α-tocopherol, clofibrate and flavoxate were prepared in high yields using this method.
- Jang, Doo Ok,Cho, Dae Hyan,Kim, Joong-Gon
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p. 2885 - 2890
(2007/10/03)
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- A fluorous super br?nsted acid catalyst: Application to fluorous catalysis without fluorous solvents
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The preparation of a fluorous super Br?nsted acid catalyst, 4-(1H,1H-perfluorotetradecanoxy)-2,3,5,6-tetrafluorophenylbis (trifluoromethanesulfonyl)methane (3d), is described. The fluorous catalyst 3d can be recycled by using liquid/solid phase separation without fluorous solvents. A perfluorocarbon solvent is not essential for fluorous biphasic catalysis.
- Ishihara, Kazuaki,Hasegawa, Aiko,Yamamoto, Hisashi
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p. 1299 - 1301
(2007/10/03)
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- Efficient and selective conversion of trimethylsilyl and tetrahydropyranyl ethers to their corresponding acetates and benzoates catalyzed by bismuth(III) salts
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A variety of TMS and THP ethers are efficiently converted to their corresponding acetates and benzoates with acetic and benzoic anhydrides in the presence of catalytic amounts of Bi(III) salts such as BiCl3, Bi(TFA)3, and Bi(OTf)sub
- Mohammadpoor-Baltork, Iraj,Khosropour, Ahmad R.
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p. 189 - 193
(2007/10/03)
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- Polystyrene-bound tetrafluorophenylbis(trifiyl)methane as an organic-solvent-swellable and strong Bronsted acid catalyst
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Several advantages over inorganic solid acids such as zeolites and perfluororesinsulfonic acids such as Nafion are offered by the new reusable polystyrene-bound catalyst 1: a broader range of applications, improved yields, improved selectivity, and milder reaction conditions. Tf = F3CSO2.
- Ishihara, Kazuaki,Hasegawa, Aiko,Yamamoto, Hisashi
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p. 4077 - 4079
(2007/10/03)
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- Bismuth(III) salts as convenient and efficient catalysts for the selective acetylation and benzoylation of alcohols and phenols
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Efficient acetylation and benzoylation of alcohols and phenols with acetic and benzoic anhydrides have been carried out under catalysis of bismuth(III) salts including BiCl3, Bi(TFA)3 and Bi(OTf)3. Selective acetylation and benzoylation of alcohols in the presence of phenols is an additional advantage of this procedure.
- Mohammadpoor-Baltork, Iraj,Aliyan, Hamid,Reza Khosropour, Ahmad
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p. 5851 - 5854
(2007/10/03)
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- Direct transacylation of 2,2,2-trihaloethyl esters with amines and alcohols using phosphorus(III) reagents for reductive fragmentation and in situ activation
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Amides and esters have been synthesized from 2,2,2-trihaloethyl esters in one pot using phosphorus(III) reagents as reductants, with resultant carboxylate activation as an acyloxyphosphonium intermediate, and in situ trapping by amine or alcohol nucleophiles. Secondary and tertiary amides were synthesized, including a dipeptide, in good yields using hexamethylphosphorous triamide, (Me2N)3P, as reducing agent. Optimal yields of esters derived from primary and secondary alcohols were obtained using tributylphosphine and DMAP. Tribromoethyl esters provided yields superior to those obtained with trichloroethyl esters.
- Hans, Jeremy J.,Driver, Russell W.,Burke, Steven D.
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p. 2114 - 2121
(2007/10/03)
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- 2-Acyloxy-4,6-dimethoxy-1,3,5-triazine - A new reagent for ester synthesis
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2-Acyloxy-4,6-dimethoxy-1,3,5-triazines obtained in reaction between carboxylic acid and 2-chloro-4,6-dimethoxy-1,3,5-triazine were used as acylating agents for the synthesis of esters from primary, secondary, and tertiary alcohols. Because of mild acylation conditions the method could be applied to esterification of labile alcohols with aromatic and aliphatic (also α-branched) acids in good yields.
- Kaminska, Janina E.,Kaminski, Zbigniew J.,Gora, Jozef
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p. 593 - 596
(2007/10/03)
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- N-acylpyridinium trifluoromethanesulfonates and tetrafluoroborates: Shuttle reagents for the acylation of enantiopure secondary alcohols
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Several enanflopure alcohols are esterified with N-acyl-4- benzylpyfidinium trifluoromethanesulfonates 7b,d,f or tetrafluoroborates 7a,c,e. These reagents, which can be generated in situ, or isolated as stable salts, are synthesized from readily available 4-alkylpyridines 3, acyl chlorides 4 and strong protic acids 6. The acyl moiety is transferred under neutral conditions and in high yields. The heterocyclic component 3a can be re-isolated almost quantitatively. The acetate, benzoate and pivaloate groups were selected with regard to their application as frequently used protecting groups for hydroxy compounds. As shown by paramagnetic shift experiments with a chiral europium(III) complex, these acylations proceed without detectable racemization or epimerization.
- Wagner, Rüdiger,Günther, Wolfgang,Anders, Ernst
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p. 883 - 888
(2007/10/03)
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- Facile oxidation of benzyl ethers by the 2-nitrobenzene-sulfonylperoxyl intermediate generated from 2-nitrobenzenesulfonyl chloride and superoxide
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Various benzyl ethers react with a 2-nitrobenzenesulfonyl-peroxyl radical intermediate generated from 2-nitrobenzenesulfonyl chloride and potassium superoxide at -25°C in acetonitrile to give the corresponding esters in high yields.
- Kim, Yong Hae,Kim, Yong Il,Kim, Joong Young
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p. 633 - 634
(2007/10/03)
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- An Extremely Powerful Acylation Reaction of Alcohols with Acid Anhydrides Catalyzed by Trimethylsilyl Trifluoromethanesulfonate
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Trimethylsilyl trifluoromethanesulfonate is an excellent catalyst for the acylation of alcohols with acid anhydrides. Highly functionalized primary, secondary, tertiary, and allylic alcohols, and phenols, were acylated cleanly and efficiently and in a fraction of the time used under the standard DMAP conditions.
- Procopiou, Panayiotis A.,Baugh, Simon P.D.,Flack, Stephen S.,Inglis, Graham G.A.
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p. 2342 - 2347
(2007/10/03)
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