- Reduction of aryl halides at transition metal cathodes. Conditions for aryl-aryl bond formation: The Ullmann's reaction revisited
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The cathodic reduction of some aryl halides ArX (1-naphthyl halides NpI and NpBr, iodo benzene and bromobenzene PhI and PhBr taken as model substrates) was achieved essentially in propylene carbonate (PC) considered for its high dielectric permittivity. Different electrode materials such as copper, silver, palladium, silver palladium alloy and nickel were used. Such conditions permit the activation of the C-X bond by metal (the step featuring similarity with Ullmann's reaction). Electron transfer to organometallic intermediates generated at the metal interface activates the formation of Ar-Ar linkages often in good yields, especially in the case of aryl iodides.
- Jouikov, Viatcheslav,Simonet, Jacques
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Read Online
- Diol-Ritter Reaction: Regio- And Stereoselective Synthesis of Protected Vicinal Aminoalcohols and Mechanistic Aspects of Diol Monoester Disproportionation
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The well-known epoxide-Ritter reaction generally affords oxazolines with poor to average regioselectivity. Herein, a mechanism-based study of the less known diol-Ritter reaction has provided a highly regioselective procedure for the synthesis of 1-vic-amido-2-esters from either terminal epoxides or 1,2-diols via Lewis acid-catalyzed monoesterification. When treated with a stoichiometric Lewis acid catalyst (BF3), these diol monoesters form dioxonium cation intermediates that are ring-opened with nitrile nucleophiles to form nitrilium intermediates, which undergo rapid and irreversible hydration to give the desired amidoesters. Diester byproduct formation is irreversible and appears to occur through disproportionation of diol monoester. With chiral epoxide starting materials, the formation of amidoester occurs with retention of configuration and no apparent erosion of optical purity as determined by single-crystal X-ray analyses and chiral chromatography, respectively. The direct access to chiral vic-amidoesters is especially practical with regard to the synthesis of antibacterial oxazolidinone analogues of the Zyvox antimicrobial family.
- Abboud, Khalil A.,Cheng, Kevin,Klosin, Jerzy,Kruper, William J.,Kruper, William R.,Lysenko, Ivan,Ondari, Mark E.,Thomas, Pulikkottil J.
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- Fast Addition of s-Block Organometallic Reagents to CO2-Derived Cyclic Carbonates at Room Temperature, Under Air, and in 2-Methyltetrahydrofuran
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Fast addition of highly polar organometallic reagents (RMgX/RLi) to cyclic carbonates (derived from CO2 as a sustainable C1 synthon) has been studied in 2-methyltetrahydrofuran as a green reaction medium or in the absence of external volatile organic solvents, at room temperature, and in the presence of air/moisture. These reaction conditions are generally forbidden with these highly reactive main-group organometallic compounds. The correct stoichiometry and nature of the polar organometallic alkylating or arylating reagent allows straightforward synthesis of: highly substituted tertiary alcohols, β-hydroxy esters, or symmetric ketones, working always under air and at room temperature. Finally, an unprecedented one-pot/two-step hybrid protocol is developed through combination of an Al-catalyzed cycloaddition of CO2 and propylene oxide with the concomitant fast addition of RLi reagents to the in situ and transiently formed cyclic carbonate, thus allowing indirect conversion of CO2 into the desired highly substituted tertiary alcohols without need for isolation or purification of any reaction intermediates.
- Elorriaga, David,de la Cruz-Martínez, Felipe,Rodríguez-álvarez, María Jesús,Lara-Sánchez, Agustín,Castro-Osma, José Antonio,García-álvarez, Joaquín
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p. 2084 - 2092
(2021/04/02)
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- Regioselective Sulfonylation/Acylation of Carbohydrates Catalyzed by FeCl3 Combined with Benzoyltrifluoroacetone and Its Mechanism Study
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A catalytic amount of FeCl3 combined with benzoyl trifluoroacetone (Hbtfa) (FeCl3/Hbtfa = 1/2) was used to catalyze sulfonylation/acylation of diols and polyols using diisopropylethylamine (DIPEA) or potassium carbonate (K2CO3) as a base. The catalytic system exhibited high catalytic activity, leading to excellent isolated yields of sulfonylation/acylation products with high regioselectivities. Mechanism studies indicated that FeCl3 initially formed [Fe(btfa)3] (btfa = benzoyl trifluoroacetonate) with twice the amount of Hbtfa under basic conditions in the solvent acetonitrile at room temperature. Then, Fe(btfa)3 and two hydroxyl groups of the substrates formed a five- or six-membered ring intermediate in the presence of the base. The subsequent reaction between the cyclic intermediate and a sulfonylation reagent led to the selective sulfonylation of the substrate. All key intermediates were captured in the high-resolution mass spectrometry assay, therefore demonstrating this mechanism for the first time.
- Dong, Hai,Liu, Yu,Lv, Jian,Zhu, Jia-Jia
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p. 3307 - 3319
(2020/03/25)
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- Benzoxaborole Catalyst for Site-Selective Modification of Polyols
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The site-selective modification of polyols bearing several hydroxyl groups without the use of protecting groups remains a significant challenge in synthetic chemistry. To address this problem, novel benzoxaborole derivatives were designed as efficient catalysts for the highly site-selective and protecting-group-free modification of polyols. To identify the effective substituent groups enhancing the catalytic activity and selectivity, a series of benzoxaborole catalysts 1a–k were synthesized. In-depth analysis for the substituent effect revealed that 1i–k, bearing multiple electron-withdrawing fluoro- and trifluoromethyl groups, exhibited the greatest catalytic activity and selectivity. Moreover, 1i-catalyzed benzoylation, tosylation, benzylation, and glycosylation of various cis-1,2-diol derivatives proceeded with good yield and site-selective manner.
- Kusano, Shuhei,Miyamoto, Shoto,Matsuoka, Aki,Yamada, Yuji,Ishikawa, Ryuta,Hayashida, Osamu
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supporting information
p. 1598 - 1602
(2020/02/11)
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- COMPOUNDS AND COMPOSITIONS FOR OCULAR DELIVERY
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The present invention provides new prodrags of Sunitinib, Brinzolamide, and Dorzolamide and compositions to treat medical disorders, for example glaucoma, a disorder or abnormality related to an increase in intraocular pressure (TOP), a disorder requiring neuroprotection, age-related macular degeneration, or diabetic retinopathy.
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Page/Page column 108; 207
(2020/05/12)
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- Stannous chloride as a low toxicity and extremely cheap catalyst for regio-/site-selective acylation with unusually broad substrate scope
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This work reports stannous chloride (SnCl2)-catalyzed regio-/site-selective acylation with unusually broad substrate scope. In addition to 1,2- and 1,3-diols and glycosides containing cis-vicinal diol, the substrate scope also includes glycosides without cis-vicinal diol. For such a substrate scope, usually, only methods using stoichiometric amounts of organotin reagents can lead to the same protection pattern with high selectivities and highly isolated yields (84-97% in most cases). Therefore, SnCl2, as a low toxicity and extremely cheap reagent, should be the best catalyst for regio-/site-selective acylation compared with any previously reported reagents. This journal is
- Dong, Hai,Feng, Guang-Jing,Luo, Tao,Lv, Jian,Yu, Jian-Cheng
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supporting information
p. 6936 - 6942
(2020/11/09)
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- DBN-Catalyzed Regioselective Acylation of Carbohydrates and Diols in Ethyl Acetate
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The 1,5-diazabicyclo[4.3.0]non-5-ene (DBN)-catalyzed regioselective acylation of carbohydrates and diols in ethyl acetate has been developed. The hydroxyl groups can be selectively acylated by the corresponding anhydride in EtOAc in the presence of a catalytic amount (as low as 0.1 equiv.) of DBN at room temperature to 40 °C. This method avoids metal catalysts and toxic solvents, which makes it comparatively green and mild, and it uses less organic base compared with other selective acylation methods. Mechanism studies indicated that DBN could catalyze the selective acylation of hydroxyl moieties through a dual H-bonding interaction.
- Ren, Bo,Zhang, Mengyao,Xu, Shijie,Gan, Lu,Zhang, Li,Tang, Lin
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supporting information
p. 4757 - 4762
(2019/07/31)
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- Domino Two-Step Oxidation of β-Alkoxy Alcohols to Hemiacetal Esters: Linking a Stoichiometric Step to an Organocatalytic Step with a Common Organic Oxidant
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Primary and secondary β-alkoxy alcohols can be cleanly and efficiently oxidized into hemiacetal esters in a cascade two-step process. mCPBA serves both as a stoichiometric oxidant in the first TEMPO-catalyzed step, converting alcohols to aldehydes/ketones, and as a reagent in the second Baeyer–Villiger stoichiometric oxidation, transforming the aldehydes/ketones into hemiacetal esters. The use of an oxidant common to both steps enables the domino reaction to proceed under a single experimental setting. Longer oxidative cascade sequences are possible when this new methodology is applied to suitable substrates.
- Targel, Tom,Ramesh, Palakuri,Portnoy, Moshe
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supporting information
p. 3017 - 3021
(2018/06/27)
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- An inexpensive catalyst, Fe(acac)3, for regio/site-selective acylation of diols and carbohydrates containing a 1,2-: Cis -diol
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This work describes the [Fe(acac)3] (acac = acetylacetonate)-catalyzed, regio/site-selective acylation of 1,2- and 1,3-diols and glycosides containing a cis-vicinal diol. The iron(iii) catalysts initially formed cyclic dioxolane-type intermediates with substrates between the iron(iii) species and vicinal diols, and the efficient and selective acylation of one hydroxyl group was subsequently achieved by adding acylation reagents in the presence of diisopropylethylamine (DIPEA) under mild conditions. This reaction generally produced high selectivities and highly isolated yields with the same protection pattern as that achieved with dibutyl tinoxide-mediated schemes.
- Lv, Jian,Ge, Jian-Tao,Luo, Tao,Dong, Hai
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supporting information
p. 1987 - 1991
(2018/05/23)
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- Diisopropylethylamine-triggered, highly efficient, self-catalyzed regioselective acylation of carbohydrates and diols
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A diisopropylethylamine (DIPEA)-triggered, self-catalyzed, regioselective acylation of carbohydrates and diols is presented. The hydroxyl groups can be acylated by the corresponding anhydride in MeCN in the presence of a catalytic amount of DIPEA. This method is comparatively green and mild as it uses less organic base compared with other selective acylation methods. Mechanistic studies indicate that DIPEA reacts with the anhydride to form a carboxylate ion, and then the carboxylate ion could catalyze the selective acylation through a dual H-bonding interaction.
- Ren, Bo,Gan, Lu,Zhang, Li,Yan, Ningning,Dong, Hai
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supporting information
p. 5591 - 5597
(2018/08/17)
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- Chitosan-Silica Sulfate Nano Hybrid as a Novel and Highly Proficient Heterogeneous Nano Catalyst for Regioselective Ring Opening of Epoxides via Carboxylic Acids
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The synthesis and characterization of chitosan-silica sulfate nano hybrid (CSSNH) as a novel and efficient heterogeneous nano catalyst involving acid-base bifunctional activity is described. The catalytic potency and activity of this eco-friendly catalyst was investigated in regioselective ring opening of epoxides with carboxylic acids to access structurally diverse 1,2-diol mono-esters in good to excellent yields. CSSNH catalyst was characterized using different microscopic and spectroscopic techniques encompassing scanning electron microscopy, transmission electron microscopy, X-ray diffraction, N2 adsorption isotherm, and Fourier transform infrared spectroscopy. The green nature, cheapness, efficiency, ease of preparation, handling and reusability of this new catalyst makes this catalyst to be useful for green industrial processes.
- Behrouz, Somayeh,Soltani Rad, Mohammad Navid,Piltan, Mohammad Amin,Doroodmand, Mohammad Mahdi
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- Palladium on Carbon-Catalyzed Chemoselective Oxygen Oxidation of Aromatic Acetals
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The development of an unprecedented chemoselective transformation has contributed to forming a novel synthetic process for target molecules. Chemoselective oxidation of aromatic acetals has been accomplished using a reusable palladium on carbon catalyst under atmospheric oxygen conditions to form ester derivatives with tolerance of aliphatic acetals and ketals.
- Yasukawa, Naoki,Asai, Shota,Kato, Maho,Monguchi, Yasunari,Sajiki, Hironao,Sawama, Yoshinari
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supporting information
p. 5604 - 5607
(2016/11/17)
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- Diacyl Disulfide: A Reagent for Chemoselective Acylation of Phenols Enabled by 4-(N,N-Dimethylamino)pyridine Catalysis
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A general and excellent acylation reagent, diacyl disulfide, was uncovered for efficient ester formation enabled by DMAP (4-(N,N-dimethylamino)pyridine) catalysis. This protocol offered a promising synthetic platform on site-selective acylation of phenolic and primary aliphatic hydroxyl groups, which greatly expanded the realm of protecting group chemistry. The importance of the reagent was also reflected by its excellent moisture tolerance, high efficiency, and potential in synthetic chemistry and biologically meaningful natural product modification.
- Liu, Hong-Xin,Dang, Ya-Qian,Yuan, Yun-Fei,Xu, Zhi-Fang,Qiu, Sheng-Xiang,Tan, Hai-Bo
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supporting information
p. 5584 - 5587
(2016/11/17)
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- A green and convenient method for regioselective mono and multiple benzoylation of diols and polyols
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An efficient method for regioselective benzoylation of diols and polyols was developed. The benzoylation is catalyzed by only 0.2 equiv of benzoate anion in acetonitrile with the addition of a stoichiometric amount of benzoic anhydride under very mild condition, leading to high yields. Compared with all other methods, this method shows particular advantage in regioselective multiple benzoylation of polyols, and in avoiding the use of any metal-based catalysts and any amine bases, which is more environment-friendly.
- Zhang, Xiaoling,Ren, Bo,Ge, Jiantao,Pei, Zhichao,Dong, Hai
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p. 1005 - 1010
(2016/02/03)
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- Propylene carbonate synthesis from propylene glycol, carbon dioxide and benzonitrile by alkali carbonate catalysts
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The synthesis of propylene carbonate from propylene glycol and carbon dioxide in the presence of various catalysts has been reported. Benzonitrile has been used as both solvent and dehydrating agent. Under optimal conditions, the best results were obtained in the presence of alkali carbonate catalysts. The propylene carbonate yield could reach up to 20% with a propylene-1,2-glycol conversion of 44%.
- Da Silva,Dayoub,Mignani,Raoul,Lemaire
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- Regioselective, borinic acid-catalyzed monoacylation, sulfonylation and alkylation of diols and carbohydrates: Expansion of substrate scope and mechanistic studies
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Synthetic and mechanistic aspects of the diarylborinic acid-catalyzed regioselective monofunctionalization of 1,2- and 1,3-diols are presented. Diarylborinic acid catalysis is shown to be an efficient and general method for monotosylation of pyranoside derivatives bearing three secondary hydroxyl groups (7 examples, 88% average yield). In addition, the scope of the selective acylation, sulfonylation, and alkylation is extended to 1,2- and 1,3-diols not derived from carbohydrates (28 examples); the efficiency, generality, and operational simplicity of this method are competitive with those of state-of-the-art protocols including the broadly applied organotin-catalyzed or -mediated reactions. Mechanistic details of the organoboron-catalyzed processes are explored using competition experiments, kinetics, and catalyst structure-activity relationships. These experiments are consistent with a mechanism in which a tetracoordinate borinate complex reacts with the electrophilic species in the turnover-limiting step of the catalytic cycle.
- Lee, Doris,Williamson, Caitlin L.,Chan, Lina,Taylor, Mark S.
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supporting information; experimental part
p. 8260 - 8267
(2012/07/14)
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- Studies on DMDO-mediated benzylidene acetal oxidation
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We have shown that dimethyldioxirane (DMDO) can be used to effect an oxidative partial deprotection of benzylidene acetals derived from both 1,2- and 1,3-diols to afford hydroxy benzoate products. A wide range of functional groups are tolerated, and good to excellent yields are usually observed. The reactions are easy to perform and produce little waste other than acetone.
- Mycock, David K.,Sherlock, Alexandra E.,Glossop, Paul A.,Hayes, Christopher J.
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body text
p. 6390 - 6392
(2009/04/06)
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- Biomimetic monoacylation of diols in water. Lanthanide-promoted reactions of methyl benzoyl phosphate
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The direct monoacylation of diols by acyl phosphate monoesters in water is a biomimetic analogy to the enzymic aminoacylation of tRNA by aminoacyl adenylates. Without catalysis, acyl phosphate monoesters react rapidly with amines but very slowly with water and alcohols. Lanthanide ions dramatically and selectively facilitate the base-catalyzed monoacylation of diols in water by methyl benzoyl phosphate (MBP), a typical acyl phosphate monoester, in neutral solutions where reactive amines are protonated and unreactive. The reaction patterns and reactivity of various diols with MBP in the presence of lanthanides are consistent with a mechanism that involves internal addition from the conjugate base of the bis-bidentate complex of the lanthanide with the diol and MBP. The method is also applicable to reactions of nucleosides as evidenced by the selective monoacylation of the 2′- or 3′-hydroxyl group of adenosine, without reaction of the 5′-hydroxyl group or the 6-amino group. Analogues of adenosine without the diol are unreactive. This suggests that the method will selectively monoacylate the hydroxyl groups at the unique diol in tRNA that forms the 3′-terminus.
- Cameron, Lisa L.,Wang, Sheila C.,Kluger, Ronald
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p. 10721 - 10726
(2007/10/03)
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- An Efficient Method for the Chemoselective Preparation of Benzoylated 1,2-Diols from Epoxides
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A very efficient and highly regioselective ring-opening reaction of epoxides with benzoic acid and its derivatives in the presence of cat. amount of tetrabutylammonium bromide (TBAB) in anhydrous acetonitrile has been developed. This effective method is useful for the preparation of selectively protected diols as precursor for many organic syntheses such as those of acyclic nucleosides and other synthetic purposes. The advantages of this method are efficiency, selectivity, low cost, and the applicability in large-scale synthesis of β-benzoyloxyalkanols.
- Khalafi-Nezhad,Soltani Rad,Khoshnood
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p. 2552 - 2558
(2007/10/03)
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- Al2O3/MeSO3H (AMA) as a new reagent with high selective ability for monoesterification of diols
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A new facile method for monoesterification of diols has been developed. A variety of diols, in particular oligoethylene glycols, were selectively monoesterified in excellent yields by reaction with aromatic and aliphatic acids in the presence of Al2O3/MeSO3H as a new reagent without use of any solvents.
- Sharghi, Hashem,Sarvari, Mona Hosseini
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p. 3627 - 3633
(2007/10/03)
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- Highly selective methodology for the direct conversion of aromatic aldehydes to glycol monoesters
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Al2O3/MeSO3H (AMA) was found to be an extremely efficient reagent for the conversion of aromatic aldehydes and diols to glycol monoesters. The remarkable selectivity achieved with this reagent is an attractive feature of t
- Sharghi, Hashem,Sarvari, Mona Hosseini
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p. 4096 - 4099
(2007/10/03)
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- Oxidative ring cleavage of cyclic acetals with hypervalent tert-butylperoxy-λ3-iodanes
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(matrix presented) Exposure of cyclic acetals to 1-tert-butylperoxy-1,2-benziodoxol-3(1H)-one in the presence of tert-butyl hydroperoxide and potassium carbonate in benzene at room temperature results in oxidative ring cleavage to glycol monoesters via intermediate tert-butylperoxy ortho esters.
- Sueda, Takuya,Fukuda, Sonoko,Ochiai, Masahito
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p. 2387 - 2390
(2007/10/03)
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- Bromide ions and methyltrioxorhenium as cocatalysts for hydrogen peroxide oxidations and brominations
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Oxidation of alcohols by hydrogen peroxide is negligible; even when catalyzed by methyltrioxorhenium (MTO), the process requires a long reaction time. The addition of a catalytic quantity of bromide ions, as HBr or NaBr, greatly enhances the rate. Some of the reactions were carried out on a larger scale in glacial acetic acid, and others at kinetic concentrations. The data establish that Br2 is the active oxidizing agent in the system, because the catalytic rates under suitable circumstances match those for the independently measured Br2 reaction with alcohol (benzyl alcohol, in particular). At much lower levels of MTO, however, Br2 formation plays a role in the kinetics. Certain other reluctant transformations are conveniently carried out with the MTO/H2O2/Br- combination: aldehydes to methyl esters; 1,3-dioxolanes to glycol monoesters; and ethers (with cleavage) to ketones (mostly), but in fair yield only. When Br- was used in stoichiometric quantity, certain bromination reactions occur. Thus, phenyl acetylenes (PhC2R, R = H, Me, Ph) are converted to dibromoalkenes that are entirely or largely formed as the trans isomer, and phenols are brominated. The latter reaction shows the preference para > ortho > meta. Kinetic studies of benzyl alcohol oxidation with MTO/H2O2Br- were carried out in aqueous solution. With sufficient (normal) levels of MTO, the rate constant for the formation of benzaldehyde agreed with the independently determined value for Br2 + PhCH2OH, k = 4.3 x 10-3 L mol-1 s-1 at 25.0 °C; for sec- phenethyl alcohol, k = (9.8 ± 0.4) x 10-3 L mol-1 s-1. Bromine is formed from the known oxidation of Br- with H2O2, catalyzed by MTO. This reaction results in BrO-/HBOr, which is then rapidly converted to Br2. However, with substantially lower concentrations of MTO, the buildup of benzaldehyde is ca. 4-fold slower, reflecting the diminished rate of Br- oxidation.
- Espenson,Zhu,Zauche
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p. 1191 - 1196
(2007/10/03)
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- Oxone: A convenient reagent for the oxidation of acetals
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Symmetrical cyclic and acyclic acetals by oxidation with Oxone gave the corresponding esters in good yield. Treatment of tetrahydropyranyl derivatives of alcohols with the same reagent resulted in oxidative regeneration of the alcohols.
- Curini, Massimo,Epifano, Francesco,Marcotullio, Maria Carla,Rosati, Ornelio
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p. 777 - 779
(2007/10/03)
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- Reactions of 1,3-dioxolanes with Iodine Monochloride: Formation of Chlorohydrin Esters and Diol Monoesters
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2-Mono-substituted 1,3-dioxolanes are oxidised by iodine monochloride to the appropriate 2-substituted 1,3-dioxolan-2-ylium ions, whose stability is dependent upon the presence and nature of substituents on C-4 and C-5.Some dioxolanylium ions are labile and under the reaction conditions afford chlorohydrin esters, with inversion of configuration taking place at the ring carbon attacked by chloride.Others are stable under the reaction conditions and may be converted on aqueous workup to diol monoesters with retention of configuration at C-4 and C-5.The effect of substituents and reaction conditions on these competing reactions are described.The stereo- and regio-chemistry of both hydroxy- and chloro-ester formation was confirmed through NMR studies, which necessitated the prior detailed analysis of the 1H and 13C spectra associated with the acyloxy sidechains of the relevant esters.
- Glass, Beverley D.,Goosen, Andre,McCleland, Cedric W.
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p. 2175 - 2182
(2007/10/02)
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- A Novel Deacylation Method using Grignard Reagent without affecting the Neighbouring Base-sensitive Functional Groups
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Methyl and ethyl Grignard reagents are shown to cleave ester functions such as benzoate and acetate without affecting the neighbouring base-sensitive functional groups.
- Watanabe, Yutaka,Fujimoto, Takahiro,Ozaki, Shoichiro
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p. 681 - 683
(2007/10/02)
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- Organotin-Mediated Monoacylation of Diols with Reversed Chemoselectivity: A Convenient Synthetic Method
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The organotin-mediated monoesterification of unsymmetrical diols with reversed chemoselectivity has been explored to ascertain scope and limits of the method and to provide an easy and convenient synthetic procedure.The reaction has been performed on a set of substituted diols with some acylating agents usually employed as protecting groups.Two different procedures have been devised to obtain either the desired diol monoesters directly or the corresponding trialkylsilyl ethers as protected derivatives.The latter provides a convenient approach to the preparation of easily interconvertible diol monoesters.Also, the reaction has been optimized as a one-pot procedure, avoiding the isolation and purification of the stannylated intermediates.The reversed monoesterification method has been successfully applied to 1,2-, 1,3-, and 1,4-diols of primary-secondary, primary-tertiary, and secondary-tertiary types and to ether functions containing 1,2-diols.Within its limits, the described method represents the first direct one-pot monoesterification of diols at the most substituted site, allowing some remarkable achievements as (a) an almost regiospecific reversed monobenzoylation of some 1,2-diols, (b) the selective acylation of the tertiary hydroxyl of a primary-tertiary diol, and (c) a highly selective preparation of secondary pivalate of primary-secondary diols.
- Reginato, Gianna,Ricci, Alfredo,Roelens, Stefano,Scapecchi, Serena
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p. 5132 - 5139
(2007/10/02)
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- A Novel Method for Preparation of Hydroxyalkyl Carboxylates by Potassium Permanganate Oxidation of Cyclic Acetals
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Cyclic acetals may be converted into hydroxyalkyl carboxylates by treatment with potassium permanganate under phase transfer condition in good yields.
- Nai-ju, Huang,Liang-heng, Xu
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p. 1563 - 1567
(2007/10/02)
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- Chemoselective Benzoylations of 1,2-Diols. Reactivity Comparisons of Reagents. Triphenylphosphine-Benzoyl Peroxide and Triphenylphosphine-Diethyl Azodicarboxylate-Benzoic Acid
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The triphenylphosphine-benzoyl peroxide (TPP-BPO) reagent initiates stereospecific benzoylation of secondary carbinol stereocenters with essentially complete inversion of stereochemistry.Monobenzoylations of 1,2-propanediol and styrene glycol with TPP-BPO and triphenylphosphine-diethyl azodicarboxylate-benzoic acid reagents afford a predominance of the more sterically encumbered C-2 benzoate with complete inversion of stereochemistry.Formation of a quintessential 1,3,2λ5-dioxaphospholane intermediate, followed by proton-assisted and highly stereoselective ring opening of the phospholanes to isomeric oxyphosphonium ions, allows for Arbusov displacement of triphenylphosphine oxide by benzoate anion.This rationale adequately accounts for both the high chemoselectivity and the stereochemistry of the reactions.
- Pautard, Anne M.,Evans, Slayton A.
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p. 2300 - 2303
(2007/10/02)
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- Regioselective Acylation of Glycols: Evidence for Organotin-mediated Reversal of Chemoselectivity
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Mono O-acylation of unsymmetrical diols via their dibutylstannyl derivatives takes place with high reversed chemoselectivity at the most substituted site, the reaction being complementary to standard methods.
- Ricci, Alfredo,Roelens, Stefano,Vannucchi, Alessio
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p. 1457 - 1458
(2007/10/02)
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- Palladium(II)-catalysed Oxidative Ring Cleavage of Cyclic Acetals with t-Butyl Hydroperoxide: Preparation of Monoesters of Diols
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Reaction of five- and six-membered cyclic acetals with tBuOOH in the presence of palladium(II) catalyst gives monoesters of diols in good yields.
- Hosokawa, Takahiro,Imada, Yasushi,Murahashi, Shun-Ichi
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p. 1245 - 1246
(2007/10/02)
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- DIALKYL ACYLPHOSPHONATES: A NEW ACYLATING AGENT OF ALCOHOLS
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Diethyl benzoylphosphonate (1) underwent facile benzoylation of alcohols in the presence of DBU.Reactions of diols containing primary and secondary hydroxyl groups with 1 gave predominantly monobenzoates in which primary hydroxyl groups were highly selectively benzoylated.Related acylations were also described.
- Sekine, Mitsuo,Kume, Akiko,Hata, Tsujiaki
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p. 3617 - 3620
(2007/10/02)
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- Reaction of 1,3-dioxolans with Iodine Monochloride: the Scope and Mechanism of Formation of 1,3-dioxolan-2-ylium Dichloroiodates(I)
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Treatment of a series of 2-substituted-4,4,5,5-tetramethyl-1,3-dioxolanes with iodine monochloride afforded the appropriate 2-substituted-4,4,5,5-tetramethyl-1,3-dioxolan-2-ylium dichloroiodate(I) salts in excellent yields.In contrast to the stable 2-aryl-substituted salts, the 2-alkyl and unsubstituted derivatives were relatively labile.While 2-phenyl-1,3-dioxolan and 2-phenyl-1,3-dioxan afforded low yields of unstable salts,crystalline products could not be isolated from 4,5-disubstituted dioxolans.The reaction was inhibited by electron-withdrawing 4- and 5-substituents.From a study of the effects of photolysis and added iodine, the mechanism is proposed to involve a hydride ion transfer.Possible reasons for the formation of dichloroiodate(I) rather then monohalide salts, are outlined.The stability of the 2-aryl-substituted salts is dicussed in terms of charge distribution in the cation and possible aryl-anion interactions.
- Goosen, Andre,McCleland, Cedric W.
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p. 977 - 983
(2007/10/02)
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