- A novel photodimerization of 4-aryl-4H-pyrans for cage compounds
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Irradiation of 4-aryl-4H-pyrans in either the solid state or in solution gave rise to the formation of novel oxa-cage compounds, 3,9-dioxatetraasteranes, derived from a double [2 + 2] cycloaddition reaction. Meanwhile, an unexpected oxetane formed by the Paternò-Büchi reaction of benzophenone with the pyrans, was established by 1H NMR data as well as by X-ray crystallographic analysis. Experimental observations and theoretical calculations confirmed that the photodimerization was effectively catalyzed by the triplet excited state of benzophenone, while the Paternò-Büchi reaction was competitive with the process.
- Xin, Hongxing,Zhu, Xiaohe,Yan, Hong,Song, Xiuqing
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Read Online
- Multiple-photon chemistry in the benzophenone photoreduction during laser-jet photolysis: Effect of alcohol solvent on cross-coupling versus hydrogen abstraction of the electronically excited hydroxydiphenylmethyl radical
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The ground state of the hydroxydiphenylmethyl radical (1) leads to benzpinacol (2) through head-to-head coupling and the diols 3 as cross-coupling product. In contrast, under the high-intensity conditions of the laser-jet photolysis, the excited radical 1* couples in the para position to afford the benzophenone derivatives 4 (head-to-tail coupling) (higher spin density at the para position/AM1 calculations). The major two-photon product is benzhydrol (5). The pronounced increase in hydrogen atom abstraction from MeOH to iPrOH by 1* is explained in terms of the greater electrophilic character of the electronically excited radical 1* versus its ground state.
- Adam, Waldemar,Walther, Barbara
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Read Online
- Iodine-Initiated Dioxygenation of Aryl Alkenes Using tert-Butylhydroperoxides and Water: A Route to Vicinal Diols and Bisperoxides
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An environment-friendly and efficient dioxygenation of aryl alkenes for the construction of vicinal diols has been developed in water with iodine as the catalyst and tert-butylhydroperoxides (TBHPs) as the oxidant. The protocol was efficient, sustainable, and operationally simple. Detailed mechanistic studies indicated that one of the hydroxyl groups is derived from water and the other one is derived from TBHP. Additionally, the bisperoxides could be obtained in good yields with iodine as the catalyst, Na2CO3 as the additive, and propylene carbonate as the solvent, instead.
- Gao, Xiaofang,Lin, Jiani,Zhang, Li,Lou, Xinyao,Guo, Guanghui,Peng, Na,Xu, Huan,Liu, Yi
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p. 15469 - 15480
(2021/11/16)
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- GaN nanowires as a reusable photoredox catalyst for radical coupling of carbonyl under blacklight irradiation
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Employing photo-energy to drive the desired chemical transformation has been a long pursued subject. The development of homogeneous photoredox catalysts in radical coupling reactions has been truly phenomenal, however, with apparent disadvantages such as the difficulty in separating the catalyst and the frequent requirement of scarce noble metals. We therefore envisioned the use of a hyper-stable III-V photosensitizing semiconductor with a tunable Fermi level and energy band as a readily isolable and recyclable heterogeneous photoredox catalyst for radical coupling reactions. Using the carbonyl coupling reaction as a proof-of-concept, herein, we report a photo-pinacol coupling reaction catalyzed by GaN nanowires under ambient light at room temperature with methanol as a solvent and sacrificial reagent. By simply tuning the dopant, the GaN nanowire shows significantly enhanced electronic properties. The catalyst showed excellent stability, reusability and functional tolerance. All reactions could be accomplished with a single piece of nanowire on Si-wafer. This journal is
- Botton, Gianluigi,Cen, Yunen,Cheng, Shaobo,Li, Chao-Jun,Liu, Mingxin,Mi, Zetian,Rashid, Roksana T.,Tan, Lida
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p. 7864 - 7870
(2020/08/19)
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- Oxidative Cleavage of Alkene C=C Bonds Using a Manganese Catalyzed Oxidation with H2O2 Combined with Periodate Oxidation
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A one-pot multi-step method for the oxidative cleavage of alkenes to aldehydes/ketones under ambient conditions is described as an alternative to ozonolysis. The first step is a highly efficient manganese catalyzed epoxidation/cis-dihydroxylation of alkenes. This step is followed by an Fe(III) assisted ring opening of the epoxide (where necessary) to a 1,2-diol. Carbon–carbon bond cleavage is achieved by treatment of the diol with sodium periodate. The conditions used in each step are not only compatible with the subsequent step(s), but also provide for increased conversion compared to the equivalent reactions carried out on the isolated intermediate compounds. The described procedure allows for carbon–carbon bond cleavage in the presence of other alkenes, oxidation sensitive moieties and other functional groups; the mild conditions (r.t.) used in all three steps make this a viable general alternative to ozonolysis and especially for use under flow or continuous batch conditions.
- Mecozzi, Francesco,Dong, Jia Jia,Angelone, Davide,Browne, Wesley R.,Eisink, Niek N. H. M.
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p. 7151 - 7158
(2019/11/16)
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- Silver(I)-Catalyzed Widely Applicable Aerobic 1,2-Diol Oxidative Cleavage
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The oxidative cleavage of 1,2-diols is a fundamental organic transformation. The stoichiometric oxidants that are still predominantly used for such oxidative cleavage, such as H5IO6, Pb(OAc)4, and KMnO4, generate stoichiometric hazardous waste. Herein, we describe a widely applicable and highly selective silver(I)-catalyzed oxidative cleavage of 1,2-diols that consumes atmospheric oxygen as the sole oxidant, thus serving as a potentially greener alternative to the classical transformations.
- Zhou, Zhong-Zhen,Liu, Mingxin,Lv, Leiyang,Li, Chao-Jun
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supporting information
p. 2616 - 2620
(2018/02/13)
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- Visible light-promoted dihydroxylation of styrenes with water and dioxygen
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An efficient visible light promoted metal-free dihydroxylation of styrenes with water and dioxygen has been developed for the construction of vicinal alcohols. The protocol was operationally simple with a broad substrate scope. The mechanistic studies demonstrated that one of the hydroxyl groups came from water and the other one came from molecular oxygen. Additionally, the β-alkyoxy alcohols could also be obtained using a similar strategy.
- Yang, Bo,Lu, Zhan
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supporting information
p. 12634 - 12637
(2017/12/02)
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- α,α-Diarylethylene Glycols as Valuable Precursor for Synthesis of 1,1-Diarylethenes and α,α-Diaryl Acetaldehydes
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Towards assembling of diarylmethine unit present in biologically important molecules, we have developed a new Weinreb Amide (WA) based building block derived from glycolic acid. The WA functionality present in this building block permits the sequential addition of various arylmagnesium bromide reagents in a controlled manner that enables assembly of a diarylmethine unit. The developed synthetic route provides easy access to important diarylethenes and α,α-diarylethylene glycols. The synthesized α,α-diarylethylene glycols provide access to synthetically important symmetrical and unsymmetrical α,α-diaryl acetaldehydes as valuable intermediates.
- Tiwari, Praveen Kumar,Sivaraman, Balasubramaniam,Aidhen, Indrapal Singh
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p. 3594 - 3605
(2017/07/22)
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- Osmium impregnated on magnetite as a heterogeneous catalyst for the syn-dihydroxylation of alkenes
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A new catalyst derived from osmium has been prepared, fully characterized and tested in the dihydroxylation of alkenes. The catalyst was prepared by wet impregnation methodology of OsCl3·3H2O on a commercial micro-magnetite surface. The catalyst allowed the reaction with one of the lowest osmium loadings for a heterogeneous catalyst and was selective for the monodihydroxylation of 1,5-dienes. Moreover, the catalyst was easily removed from the reaction medium by the simple use of a magnet. The selectivity of catalyst is very high with conversions up to 99%. Preliminary kinetics studies showed a first-order reaction rate with respect to the catalyst.
- Cano, Rafael,Pérez, Juana M.,Ramón, Diego J.
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p. 177 - 182
(2014/01/06)
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- Homogeneous and heterogeneous photoredoxcatalyzed hydroxymethylation of ketones and keto esters: Catalyst screening, chemoselectivity and dilution effects
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The homogeneous titanium- and dye-catalyzed as well as the heterogeneous semiconductor particle-catalyzed photohydroxymethylation of ketones by methanol were investigated in order to evaluate the most active photocatalyst system. Dialkoxytitanium dichlorides are the most efficient species for chemoselective hydroxymethylation of acetophenone as well as other aromatic and aliphatic ketones. Pinacol coupling is the dominant process for semiconductor catalysis and ketone reduction dominates the Ti(OiPr)4/methanol or isopropanol systems. Application of dilution effects on the TiO2 catalysis leads to an increase in hydroxymethylation at the expense of the pinacol coupling.
- Griesbeck, Axel G.,Reckenthaeler, Melissa
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supporting information
p. 1143 - 1150
(2014/06/09)
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- Synthesis of 1,2,4-trioxepanes and 1,2,4-trioxanes via Hmediated reaction of tertiary carbinols
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A facile and efficient method for the synthesis of 1,2,4-trioxepanes and 1,2,4-trioxanes from different carbinols having cyclopropyl and phenyl substituents has been developed. The corresponding hydroxyhydroperoxides were synthesized from 30% Hmediated reaction of carbinols in acidic conditions. This method provided access to novel 6,6-diaryl-substituted 1,2,4-trioxanes derived from benzilic acid. Georg Thieme Verlag Stuttgart · New York.
- Ravi, Makthala,Anand, Devireddy,Maurya, Ranjani,Chauhan, Parul,Naikade, Niraj K.,Shukla, Sanjeev K.,Yadav, Prem P.
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p. 173 - 176
(2013/02/26)
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- (N,N-Diisopropylcarbamoyloxy)-methyl p-tolyl sulfone: Preparation and application for the syntheses of 1,2-diols
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1-(N,N-Diisopropylcarbamoyloxy)-1-tosyl-methane (CbOCH2Ts, Cb=N,N-diisopropylcarbamoyl) was readily prepared from p-TolSH, paraformaldehyde and CbCl. With the dual activation of CbO- and Ts-substitutions, deprotonation of CbOCH2Ts co
- Ma, Lu,Zhao, Dongmei,Chen, Lin,Wang, Xin,Chen, Yue-Lei,Shen, Jingkang
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p. 8704 - 8711
(2012/10/30)
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- Metal-free dihydroxylation of alkenes using cyclobutane malonoyl peroxide
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Cyclobutane malonoyl peroxide (7), prepared in a single step from the commercially available diacid 6, is an effective reagent for the dihydroxylation of alkenes. Reaction of a chloroform solution of 7 with an alkene in the presence of 1 equiv of water at 40 °C followed by alkaline hydrolysis leads to the corresponding diol (30-84%). With 1,2-disubstituted alkenes, the reaction proceeds with syn-selectivity (3:1 → 50:1). A mechanism consistent with experimental findings is proposed, which is supported by deuterium and oxygen labeling studies and explains the stereoselectivity observed. Alternative reaction pathways that are dependent on the structure of the starting alkene are also described leading to the synthesis of allylic alcohols and γ-lactones.
- Jones, Kevin M.,Tomkinson, Nicholas C. O.
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experimental part
p. 921 - 928
(2012/02/16)
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- One-pot synthesis of cyclophane-type macrocycles using manganese(iii)- mediated oxidative radical cyclization
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Cyclophane-type macrocyclic compounds from 21 to 56 members having two fused dihydrofuran rings were synthesized by the manganese(iii)-mediated oxidation of terminal dienes with bis(3-oxobutanoate)s containing aromatics. The reaction detail, characterization and reaction pathways are described. The Royal Society of Chemistry 2011.
- Ito, Yosuke,Tomiyasu, Yuichi,Kawanabe, Takahiro,Uemura, Keisuke,Ushimizu, Yuu,Nishino, Hiroshi
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supporting information; scheme or table
p. 1491 - 1507
(2011/04/23)
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- Phase selectively soluble dendrimer-bound osmium complex: A highly effective and easily recyclable catalyst for olefin dihydroxylation
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A new switched biphasic catalysis system for highly effective olefin dihydroxylation has been described, in which the dendritic osmium catalyst preferred to dissolve in the non-polar organic layer and could be easily separated from the polar diol products through phase separation induced by addition of water at the end of the reaction.
- Tang, Wei-Jun,Yang, Nian-Fa,Yi, Bing,Deng, Guo-Jun,Huang, Yi-Yong,Fan, Qing-Hua
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p. 1378 - 1379
(2007/10/03)
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- OsO4-catalyzed dihydroxylation of olefins in ionic liquid [emim]BF4: A recoverable and reusable osmium
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We have demonstrated the usefulness of recoverable and reusable immobilized OsO4 in [emim]BF4 for dihydroxylation of several olefins. This approach is simple and practical. It should be noted that the volatility and toxicity of OsO4 are greatly suppressed when the ionic liquid [emim]BF4 is used.
- Yanada, Reiko,Takemoto, Yoshiji
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p. 6849 - 6851
(2007/10/03)
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- 1,1-Diphenyl-2-methylsulfinyl ethanol: A model compound to study the reactivity towards CNBr of a photoadduct of methionine on CγH2
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The photoadduct formed by photolysis of the [Bapa0, (pBzl)Phe5, Met(O2)11]SP/NK-1 complex localised within the T173MP175 domain of the NK-1 receptor cannot be cleaved by CNBr on the C-side of methionine; an unusual rearrangement of the intermediate sulfonium instead occurred. The reactivity of 1,1-diphenyl-2-methylsulfinyl ethanol 10 towards CNBr treatment and the stability of the 1,1-diphenyl oxirane 14 were analysed by NMR and mass spectrometry. 1,1-Diphenyl ethylene 13 can be formed from epoxide 14 even in slightly acidic conditions and during positive DCI/NH3 mass spectrometry analysis. Altogether, these results suggest that if a covalent linkage between the [Bapa0, (pBzl)Phe5, Met(O2)11] and the NK-1 receptor occurred on the CγH2 of methionine-174, CNBr treatment will lead to an epoxide/ketone and an ethylenic compound.
- Sachon, Emmanuelle,Milcent, Thierry,Sagan, Sandrine,Convert, Odile,Chassaing, Gérard,Lavielle, Solange
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p. 7485 - 7489
(2007/10/03)
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- Mechanism of the catalytic oxidation of tertiary alcohols by the water- soluble Mn-TMPyP/KHSO5 system: β-Fragmentation versus O-neophyl rearrangement
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Oxidation of 4-(1-hydroxy-1-phenylethyl)benzoic acid HPEBA with a water- soluble metalloporphyrin as catalyst and KHSO5 as oxygen atom donor gives the major products, acetophenone AC and acetylbenzoic acid ABA, by a C(aliph)-C(Ar) bond cleavage, but a minor product, benzoyloxybenzoic acid BOBA, requires the insertion of an oxygen atom to form the ester. This compound becomes the main oxidation product on increasing the amount of acetonitrile in the reaction medium, and its formation is oxygen-dependent. The conversion is drastically lowered by using D2O instead of H2O, suggesting that an alkoxyl radical is formed in the rate-determining step. Labeling experiments using 18O2 or H218O under different reaction conditions show that the carbonyl oxygen atoms of AC and ABA originate either from substrate, water or dioxygen. However, the carbonyl oxygen atom in the ester group of BOBA originates from dioxygen while the other oxygen atom of the ester remains unlabeled. These results can be explained by an O-neophyl rearrangement of the initial alkoxyl radical to afford a carbon-based radical which then reacts with dioxygen or Mn(IV)-OH/water. In a competitive reaction pathway, direct β-scission of the alkoxyl radical leads to unlabeled products. The oxidation of other tertiary diaryl alcohols is also discussed.
- Wietzerbin, Karine,Bernadou, Jean,Meunier, Bernard
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p. 1467 - 1477
(2007/10/03)
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- Reactivity and selectivity in the oxidation of styrene derivatives. V. studies on the oxidation of α-substituted styrenes
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The liquid phase oxidation of α-phenyl-1a, α-trimethylsilyloxy 1b, α-cyclopropyl-1c, α-trifluoromethyl-1d styrene, and styrene 1e with oxygen in chlorobenzene and cumene solution in the temperature range 55-125°C was investigated. The product yields were determined gaschromatographically. The epoxide selectivity increases up to 90°C with increasing temperature. The epoxides of 1a and 1c rearrange at higher temperatures, therefore their yield decreases. The relative chain propagation constants (kpC=C) were determined by competitive oxidations of cumene. WILEY-VCH Verlag GmbH, 1999.
- Suprun
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- N-(α-chloroalkyloxycarbonyl)pyrrolidines as a source of oxygenated d1- reagents
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Reaction of the N-(α-chloroalkyloxycarbonyl)pyrrolidines 1 with lithium powder and a catalytic amount of 4,4'-di-tertbutylbiphenyl (DTBB, 2.5 mol-%) in the presence of different electrophiles [iBuCHO, tBuCHO, PhCHO, Et2CO, (CH2)5CO, PhCOMe, Ph2CO, MeaSiCl], in THF at temperatures ranging between -78 and -60°C leads after hydrolysis with water, to the expected functionalized carbamates 2. Deprotection of compounds 2, derived from carbonyl compounds, with lithium hydroxide in a mixture of ethanol and water at 80°C affords the corresponding 1,2-diols 3.
- Ortiz, Javier,Guijarro, Albert,Yus, Miguel
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p. 3005 - 3012
(2007/10/03)
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- N-(chloromethyloxycarbonyl)pyrrolidine as a source of the HOCH2- synthon
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The reaction of N-(chloromethyloxycarbonyl)pyrrolidine (1) with lithium powder and a catalytic amount of DTBB (2.5 mol %) in the presence of different electrophiles [Me3SiCl, Bu(i)CHO, Bu(t)CHO, PhCHO, Et2CO, (CH2)5CO, PhCOMe, Ph2CO] in THF at -78°C leads, after hydrolysis with water, to the expected functionalised carbamates 2. Deprotection of the acetophenone derivative 2g with DIBALH at THF reflux yields, after hydrolysis, the corresponding 1,2-diol 3g.
- Guijarro, Albert,Yus, Miguel
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p. 5593 - 5596
(2007/10/03)
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- Methyltrioxorhenium(VII)-katalysierte Epoxydierung von Alkenen mit Harnstoff-Wasserstoffperoxid
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Keywords: Asymmetrische Synthesen; Epoxidierungen; Katalyse; Komplexe mit Sauerstoffliganden; Rheniumverbindungen
- Adam, Waldemar,Mitchell, Catherine M.
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p. 578 - 581
(2007/10/03)
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- Olefin Epoxidation Using Elemental Fluorine
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F2 reacts with water and CH3CN, apparently to produce the relatively stable complex HOF*CH3CN.This is probably the best known oxygen-transfer reagent and can epoxidize olefins quickly and efficiently.Various types of alkenes including aliphatic, benzylic, enones, dienones, maleates, and fumarates have been examined, and all react with the reagent to produce the corresponding mono- or diepoxides in good to excellent yields.This epoxidation is fully stereospecific, and the configuration of the starting olefin is fully retained in the resulting oxirane.In cases where exceptionally stable oxocarbocations can be formed as in 1,1-diphenylethene, the reaction produces vicinal glycols in good yields.Since the origin of the epoxides' oxygen is in the water, this method is very suitable for introducing the isotopes 17O and 18O in various molecules.
- Rozen, Shlomo,Kol, Moshe
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p. 5155 - 5159
(2007/10/02)
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- Reduction of Long Chain and Bulky Carboxylic Esters by Sodium Tetrahydroborate
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Methyl esters of long chain fatty acids as well as esters with functional (OH) and/or bulky substituents in alpha position and in the OR moiety may be effectively reduced with an excess of sodium tetrahydroborate at moderate temperature in dioxane-water without catalysts.The reaction has been applied to the reduction of a pool of triglycerides of natural origin (virgin olive oil) in order to obtain a mixture of the acyl residues reduced to the corresponding alcohols without any structural or configurational modification.They, no matter which was the advancement of the reaction, seemed to reproduce quite well the overall acyl composition, as shown by GC-MS analysis: the feasibility of such quantitative analysis may be extended, in order to obtain confirmatory evidences on the component identifications and to perform specific separations, to the corresponding chlorides, hydrocarbons and trimethylsilylethers.
- Giumanini, Angelo G.,Tubaro, Franco
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p. 755 - 761
(2007/10/02)
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- Synthesis and Reaction of 1,2,4-Trioxanes
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The peroxides (1a-e) and epoxides (2a-g) in methylene dichloride were treated with tungsten (VI) oxide and then with catalitic amounts of chlorosulphonic acid to give the corresponding 1,2,4-trioxanes (3a-r) in 10-63percent yield.The mode of decomposition of the 1,2,4-trioxanes was studied by treating a number with the following reagents: triethylamine, sodium ethoxide, lithium di-isopropylamide, Grignard and lithium reagents, lithium aluminium hydride, anthrylsodium, triphenylphosphine, and titanium tetrachloride.
- Fujisaka, Tomohiro,Miura, Masahiro,Nojima, Masatomo,Kusabayashi, Shigekazu
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p. 1031 - 1039
(2007/10/02)
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- NEW OBSERVATIONS ON THE PHOTOPINACOLIZATION OF BENZOPHENONE IN ALIPHATIC ALCOHOLS
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Irradiation of benzophenone in alcohol solutions produces unsymmetrical pinacols and para-coupled products as well as benzpinacol; the product composition depends on light intensity.
- Rubin, Mordecai B.
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p. 4615 - 4618
(2007/10/02)
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- Electron-transfer photochemistry of iminium salts. Olefin photoadditions to 2-phenyl-1-pyrrolinium perchlorate
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The photoaddition reactions of 2-phenyl-1-pyrrolinium perchlorate (2) and a variety of olefins have been investigated. Irradiation of methanolic solutions of 2 in the presence of the electron-rich olefins isobutylene, cyclohexene, butadiene, isopropenylcyclopropane, and methyl β,β-dimethylacrylate leads to formation of two types of addition products. One of these results from anti-Markovnikov addition of the components of methanol and the pyrrolinium salt across the olefinic π bond, generating a carbon-carbon bond to the pyrrolidine 2-position. The other corresponds to addition of the 2-phenylpyrrolidine unit across allylic C-H bonds of the olefins. Both reactions are explained by using electron-transfer mechanisms. Support for these mechanisms, which rationalize the nature of the reactions, their regiochemistry, and their stereochemistry, has come from studies with the electron-poor olefins methyl acrylate, acrylonitrile, and methyl methacrylate. Irradiation of 2 in the presence of these olefins leads to generation of 9-substituted 1-aza-6,7-benzospiro[4.4]non-6-ene products, results of [2 + 2] cycloadditions of the olefins to the C-1,C-2 π bond of the pyrrolinium salt phenyl ring. Fluorescence quenching studies have been conducted to gain further evidence in support of the mechanistic postulates.
- Stavinoha, Jerome L.,Mariano, Patrick S.
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p. 3136 - 3148
(2007/10/10)
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