- Use of Organic Molecules as Mechanistic Probes for Semiconductor-Mediated Photoelectrochemical Oxidations: Bromide Oxidation
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Cyclohexene has been used as an organic probe for mechanism in the semiconductor-photocatalyzed oxidation of bromide in acetonitrile.Products derived from bromine addition and from cyclohexenyl radical mediated autoxidation were isolated.These results implicate a mechanism in which the photoexcited semiconductor effects a one electron oxidation of adsorbed bromide, producing surface-bound bromine atoms.These potentially could abstract hydrogen from cyclohexene to initiate autoxidation or could migrate along the semiconductor surface, producing bromine (Br2), which migrates into solution where it is rapidly trapped in conventional electrophilic addition.
- Fox, Marye Anne,Pettit, Thomas L.
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- An efficient regioselective halogenation of 5-amino-endo-tricyclo[5.2.1.02,6]deca-4,8-dien-3-ones
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An effective regioselective halogenation of 5-amino-endo-tricyclo decenyl enaminones 6 using N-halosuccinimides is reported. The reaction is extremely fast and the yields are almost quantitative. Exclusive α,N-dihalo or α,γ-dihalo compounds can be obtaine
- Ramesh, Namakkal G,Heijne, Erik H,Klunder, Antonius J.H,Zwanenburg, Binne
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- Dendrimeric organochalcogen catalysts for the activation of hydrogen peroxide: Origins of the "dendrimer effect" with catalysts terminating in phenylseleno groups
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Several scenarios were evaluated to explain the large "dendrimer effect" observed in the bromination of cyclohexene with H2O 2 and NaBr catalyzed by the addition of Frechet-type dendrimers terminating in -O(CH2)3SePh groups. Although phenylseleninic acid was an efficient catalyst for the oxidation of NaBr with H2O2, first-order rate constants for the selenoxide elimination were too small to produce PhSeO2H at a rate sufficient to explain the rates of catalysis and no dendrimer effect was observed in the rates of selenoxide elimination. An induction period was observed using 1-SePh as a catalyst for the oxidation of Br- with H2O2. The addition of preformed selenoxide 1-Se(=O)Ph gave immediate catalysis with no induction period. However, rates of oxidation of the selenides with H 2O2 under homogeneous or biphasic conditions or with t-BuOOH under homogeneous conditions were too slow to account for the rates of catalysis, and no dendrimer effect was observed in the rates of oxidation. The primary oxidant for converting selenides to selenoxides was "Br+" produced initially by the uncatalyzed background reaction of H2O 2 with NaBr and then produced catalytically following formation of selenoxide groups. Autocatalysis is observed, and the rate of oxidation increases with the number of SePh groups. Autocatalysis is the source of the large dendrimer effect observed with the SePh series of catalysts.
- Drake, Michael D.,Bright, Frank V.,Detty, Michael R.
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- Positive halogens from halides and hydrogen peroxide with organotellurium catalysts
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The oxidations of sodium bromide, sodium chloride, and sodium iodide to positive halogen with hydrogen peroxide in two-phase systems of dichloromethane and pH 6 phosphate buffer were catalyzed by organotellurium catalysts 1-3. The positive halogens were trapped by cyclohexene for bromine and chlorine to give mixtures of the 1,2-dihalocyclohexane (4) and 2-halocyclohexanol (5). For the bromination (4a)/hydrobromination (5a) of cyclohexene, unoptimized turnover numbers of 1010 mol of product per mole of catalyst for 1, 960 for 2, and 820 for 3 were measured with 4a/5a ratios of 55:45, 53:47, and 52:48, respectively. In cyclohexane, the turnover number for 1 was 150 and the 4a/5a ratio was 68:32. In the uncatalyzed process and in the reaction of aqueous bromine with cyclohexene, the 4a/5a ratio is 55:45 in dichloromethane and 67:33 in cyclohexane. The relative rates of catalysis for equimolar amounts of 1-3 were nearly identical to the relative second-order rate constants for oxidation of the organotellurium compounds with hydrogen peroxide, which suggests that oxidation of the catalyst is the rate-determining step of the process. Stopped-flow studies indicated a rapid reaction (k = 22.5 ± 0.3 M-1 s-1 for iodide and 13.9 ± 0.5 M-1 s-1 for bromide) between halide and oxidized 3 to regenerate catalyst 3. Relative rates of catalysis with 0.1 mol % of 1-3 (relative to cyclohexene) were 4.6 for 1, 2.0 for 2, 1.0 for 3, and 0.11 for the control reaction with no catalyst at 296.1 ± 0.1 K. Oxidation of chloride with hydrogen peroxide with 1 as a catalyst was much slower but the unoptimized turnover number was 100 with a 4b/5b ratio of 7:93 (10:90 in the uncatalyzed process) in a two-phase cylohexane/aqueous system. Oxidized 3 reacts rapidly with both sodium chloride and sodium bromide to give products from oxidative addition of halogen to the catalyst. Stronger Te-Cl bonds relative to Te-Br bonds slow down the release of the Te(II) state of the catalyst. Positive iodine from catalysis with 1 was trapped by 4-pentenoic acid to give iodomethyl lactone 6.
- Detty, Michael R.,Zhou, Feng,Friedman, Alan E.
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- SURFACTANT CONTROL OF BROMINATION PRODUCTS
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The product distribution in the bromination of cyclohexene is almost completely controlled by the addition order of the reactants to the surfactant, the obtained bromohydrin being 99percent pure.Water seems to be present all around the micelles head groups.
- Bianchi, M. T.,Cerichelli, G.,Mancini, G.,Marinelli, F.
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- Electrochemical bromofunctionalization of alkenes in a flow reactor
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The bromination of organic molecules has been extensively studied to date, yet there is still a demand for safe and sustainable methodologies. Hazardous reagents, selectivity, low atom economy and waste production are the most persisting problems of brominating reagents. The electrochemical oxidation of bromide to bromine is a viable strategy to reduce waste by avoiding chemical oxidants. Furthermore, thein situgeneration of reactive intermediates minimizes the risk of hazardous reagents. In this work, we investigate the electrochemical generation of bromine from hydrobromic acid in a flow electrochemical reactor. Various alkenes could be converted to their corresponding dibromides, bromohydrines, bromohydrin ethers and cyclized products in good to excellent yields.
- Seitz, Jakob,Wirth, Thomas
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supporting information
p. 6892 - 6896
(2021/08/20)
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- Halofunctionalization of alkenes by vanadium chloroperoxidase from: Curvularia inaequalis
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The vanadium-dependent chloroperoxidase from Curvularia inaequalis is a stable and efficient biocatalyst for the hydroxyhalogenation of a broad range of alkenes into halohydrins. Up to 1 200 000 TON with 69 s-1 TOF were observed for the biocatalyst. A bienzymatic cascade to yield epoxides as reaction products is presented.
- Dong, Jia Jia,Fernández-Fueyo, Elena,Li, Jingbo,Guo, Zheng,Renirie, Rokus,Wever, Ron,Hollmann, Frank
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supporting information
p. 6207 - 6210
(2017/07/10)
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- Catalytic Asymmetric Bromination of Unfunctionalized Olefins with H2O as a Nucleophile
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The dimeric cinchona alkaloid (DHQD)2PHAL is used to catalyze an effective asymmetric bromohydroxylation of unfunctionalized olefins with H2O as nucleophile an N-bromobenzamide as a bromine source. A variety of optically active bromohydrins are formed with up to 88%ee. PHAL's positive: An effective asymmetric bromohydroxylation of unfunctionalized olefins with H2O as nucleophile catalyzed by the dimeric cinchona alkaloid (DHQD)2PHAL (see scheme) is described. Optically active bromohydrins are obtained with up to 88%ee.
- Zhang, Xun,Li, Jing,Tian, Hua,Shi, Yian
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p. 11658 - 11663
(2015/08/18)
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- Bromine and iodine-cucurbit[6]uril complexes: Preparation and applications in synthetic organic chemistry
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Iodine and bromine inclusion compounds were easily prepared by gas diffusion of the halogens using finely powdered CB[6]. A brown powder consisting of I2-CB[6]·4H2O and an orange one of (Br 2)4-CB[6]·10H2O were employed in several different reactions. I2-CB[6] can be used in catalytic reactions giving yields comparable to those reported in the literature. Br 2-CB[6] was effectively applied in electrophilic bromination of benzene and formation of bromohydrin. However, the radical substitution at cyclohexene could not be performed. Overall, based on these results, several applications can be envisioned for these complexes. This journal is the Partner Organisations 2014.
- Reddy,Cavallini,Demets,Silva
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p. 2262 - 2264
(2014/06/09)
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- 1,3,2,4-diazadiphosphetidine-based phosphazane oligomers as source of P(III) atom economy reagents: Conversion of epoxides to vic -haloalcohols, vic -dihalides, and alkenes in the presence of halogen sources
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1,3,2,4-Diazadiphosphetidines (P1-P3), as easily prepared, stable, and heterogeneous P(III) compounds, were used for the efficient conversion of epoxides to vic-halohydrins, vic-dihalides, or alkenes in the presence of different halogen sources in CH3CN. Of these phosphazanes, P3 is most suitable and contains 4 phosphorous atoms with the advantage of having greater atom economy and its phosphorus oxide byproduct can be easily separated from the reaction mixture by simple filtration. The nitrogen atoms in this molecule can also act as acid scavengers in the reaction.
- Iranpoor, Nasser,Firouzabadi, Habib,Etemadidavan, Elham
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p. 1165 - 1173
(2014/10/16)
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- Cytochrome P450 catalyzed oxidative hydroxylation of achiral organic compounds with simultaneous creation of two chirality centers in a single C-H activation step
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Regio- and stereoselective oxidative hydroxylation of achiral or chiral organic compounds mediated by synthetic reagents, catalysts, or enzymes generally leads to the formation of one new chiral center that appears in the respective enantiomeric or diastereomeric alcohols. By contrast, when subjecting appropriate achiral compounds to this type of C-H activation, the simultaneous creation of two chiral centers with a defined relative and absolute configuration may result, provided that control of the regio-, diastereo-, and enantioselectivity is ensured. The present study demonstrates that such control is possible by using wild type or mutant forms of the monooxygenase cytochrome P450 BM3 as catalysts in the oxidative hydroxylation of methylcyclohexane and seven other monosubstituted cyclohexane derivatives.
- Roiban, Gheorghe-Doru,Agudo, Ruben,Reetz, Manfred T.
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supporting information
p. 8659 - 8663
(2014/08/18)
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- Synthesis of Di-, Tri-, and tetrasubstituted oxetanes by rhodium-catalyzed O-H insertion and C-C bond-forming cyclization
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Oxetanes offer exciting potential as structural motifs and intermediates in drug discovery and materials science. Here an efficient strategy for the synthesis of oxetane rings incorporating pendant functional groups is described. A wide variety of oxetane 2,2-dicarboxylates were accessed in high yields, including functionalized 3-/4-aryl-and alkyl-substituted oxetanes and fused oxetane bicycles. Enantioenriched alcohols provided enantioenriched oxetanes with complete retention of configuration. The oxetane products were further derivatized, while the ring was maintained intact, thus highlighting their potential as building blocks for medicinal chemistry.
- Davis, Owen A.,Bull, James A.
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supporting information
p. 14230 - 14234
(2015/02/19)
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- Enzymatic preparation of (1S,2R)- and (1R,2S)-stereoisomers of 2-halocycloalkanols
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The stereoisomers of cis-2-halocycloalkanols were resolved by a kinetically controlled transesterification with vinyl acetate in the presence of lipases in organic media. High enantioselectivities (ee >98%) and good isolated yields were obtained for all substrates using the appropriate lipase. Burkholderia cepacia lipase was the most efficient enzyme for the resolution of these substrates. The enantiomeric purities of the compounds were defined by derivatization with Mosher's acid and the absolute configurations were determined by chemical correlation.
- Kolodiazhna, Olga O.,Kolodiazhna, Anastasy O.,Kolodiazhnyi, Oleg I.
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- Regio-and stereoselective hydroxybromination and dibromination of olefins using ammonium bromide and oxone
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An efficient protocol for the synthesis of vicinal bromohydrins and dibromides from olefins is presented. Various olefins are regio-and stereoselectively hydroxybrominated and dibrominated with anti fashion, following Markonikov's rule, using eco-friendly, non-toxic, and stable reagents such as NH4Br and oxone in CH3CN/H2O (1:1) and CH3CN without employing catalyst in moderate to excellent yields. Bromohydrins are formed instantaneously.
- MacHarla, Arun Kumar,Chozhiyath Nappunni, Rohitha,Nama, Narender
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supporting information; experimental part
p. 1401 - 1405
(2012/04/04)
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- H2TPP organocatalysis in mild and highly regioselective ring opening of epoxides to halo alcohols by means of halogen elements
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We found that elemental iodine and bromine are converted to trihalide nucleophiles (triiodine and tribromide anion, respectively) in the presence of catalytic amounts of meso-tetraphenylporphyrins (H2TPP). Therefore a highly regioselective method for the synthesis of β-haloalcohols through direct ring opening of epoxides with elemental iodine and bromine in the presence of H2TPPs as new catalysts is described. At room temperature a series of epoxide derivatives were converted into the corresponding halohydrins resulting from an attack of trihalide species anion atoms at the less substituted carbon atom. This method occurs under neutral and mild conditions with high yields in various aprotic solvents, even when sensitive functional groups are present.
- Torabi, Parviz,Azizian, Javad,Zomorodbakhsh, Shahab
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experimental part
p. 5508 - 5519
(2012/08/28)
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- Conformational analysis of cis-2-halocyclohexanols; Solvent effects by NMR and theoretical calculations
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Conformational problems often involve very small energy differences, even low as 0.5 kcal mol-1. This accuracy can be achieved by theoretical methods in the gas phase with the appropriate accounting of electron correlation. The solution behavio
- Basso, Ernani A.,Abiko, Layara A.,Gauze, Gisele F.,Pontes, Rodrigo M.
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experimental part
p. 145 - 153
(2011/03/19)
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- Addition of halide to π-bond directly from aqueous NaX solution: A general strategy for installation of two different functional groups
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Activation of π-bond with organic Lewis acid and cationic surfactant mediated direct transfer of halides to alkyne and alkene are demonstrated to afford α,α-dihaloketones and other valuable synthons with outstanding selectivities.
- Pandit, Palash,Gayen, Krishnanka S.,Khamarui, Saikat,Chatterjee, Nirbhik,Maiti, Dilip K.
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supporting information; experimental part
p. 6933 - 6935
(2011/08/06)
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- Highly regio- and diastereoselective halohydroxylation of olefins: A facile synthesis of vicinal halohydrins
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An efficient method for the synthesis of vicinal chlorohydrin or bromohydrin derivatives has been developed on the basis of direct halohydroxylation of various olefins with electrondonating or withdrawing substituent. The reactions were carried out under mild conditions in the presence of N-tosyl-l-threonine (NTsLT) as an acidic additive using chloramine T trihydrate, 1,3-dichloro-5,5-dimethylhydantoin (DCDMH) or N-bromoacetamide (AcNHBr) as the halogen source, respectively, affording the corresponding vicinal halohydrins in good to high yields with excellent regio- and stereoselectivities.
- Zhang, Jinglei,Wang, Jie,Qiu, Zhuibai,Wang, Yang
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experimental part
p. 6859 - 6867
(2011/10/02)
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- Comparative study of the vicinal functionalization of olefins with 2:1 bromide/bromate and iodide/iodate reagents
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A comparative evaluation was made on the syntheses of vicinal halohydrins, halo methyl ethers, and halo acetates from olefins using 2:1 Br-/BrO3- and I-/IO3- reagents. In many cases both reagents afforded products selectively in high yields. The highest halogen atom efficiencies attained were 97% and 93% for Br-/BrO3- and I-/IO3-, respectively. Of the two reagents, I-/IO3- was established to be the preferred reagent for vicinal functionalization of linear alkenes and also for halo acetate preparation. However, only Br-/BrO3- was effective for vicinal functionalization of trans-stilbene and chalcones.
- Agrawal, Manoj K.,Adimurthy, Subbarayappa,Ganguly, Bishwajit,Ghosh, Pushpito K.
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supporting information; experimental part
p. 2791 - 2797
(2009/08/08)
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- Convenient, easy and highly regioselective preparation of haloalcohols from the reaction of epoxides with elemental halogen catalyzed by hexamethylenetetramine (HMTA)
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The highly regioselective cleavage of epoxides into corresponding vicinal haloalcohols with elemental halogen has been catalyzed by hexamethylenetetramine (HMTA). This method occurred under neutral and mild conditions with high yields and short reaction times in various aprotic solvents even when sensitive functional groups were present.
- Naeimi, Hossein
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experimental part
p. 1156 - 1159
(2009/12/03)
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- Monobromoborane-dimethyl sulfide - A highly promising reagent for the regio- and chemoselective brominative cleavage of terminal epoxides into vicinal bromohydrins
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Monobromoborane?dimethyl sulfide (BH2Br?SMe2) is a highly regio- and chemoselective reagent useful for the brominative cleavage of the epoxy moiety into bromohydrins in the presence of alkenes, alkynes, ethers, acetals, ketals, and acetonides at 0°C, besides being an excellent hydroborating reagent. Several reactive functional groups, such as chloride, ketones, esters, nitriles, nitros, and thioethers, have been accommodated during such transformations. Although the reduction of acetophenone was completely suppressed at ?25°C, 4-chlorobenzaldehyde still underwent 12?13% reduction of an aldehydic group. CSIRO 2007.
- Roy, Chandra D.,Brown, Herbert C.
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p. 139 - 145
(2008/02/11)
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- Highly regioselective ring opening of epoxides and aziridines using (bromodimethyl)sulfonium bromide
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Epoxides and aziridines undergo ring opening efficiently with (bromodimethyl)sulfonium bromide at room temperature to form the corresponding β-bromohydrins and β-bromoamines, respectively. The conversions are highly regioselective and afford the products in excellent yields within a short period of time.
- Das, Biswanath,Krishnaiah, Maddeboina,Venkateswarlu, Katta
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p. 4457 - 4460
(2007/10/03)
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- Regioselective synthesis of vic-halo alcohols and symmetrical or unsymmetrical vic-dihalides from epoxides using triphenylphosphine -N-halo imides
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A simple, novel, and highly regioselective cleavage of epoxides into vicinal halo alcohols and symmetrical or unsymmetrical dihalides is described using different stoichiometries of triphenylphosphine (PPh3) and N-halo succinimide (NXS) or N-halo saccharine (NXSac).
- Iranpoor, Nasser,Firouzabadi, Habib,Azadi, Roya,Ebrahimzadeh, Farzaneh
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- Silphos [PCl3-n (SiO2)n]: A heterogeneous phosphine reagent for the regioselective synthesis of vic-haloalcohols
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Silphos as a silica-based phosphine [PCl3-n (SiO 2)n] provides a practical method for the conversion of epoxides to vic-haloalcohols in the presence of molecular bromine, iodine, or N-halosuccinimides (NXS, X = Cl, Br, I) in CH3CN or under solvent-free conditions at r.t. The simple filtration of heterogeneous Silphos oxide from the reaction mixture affords the pure vic-haloalcohols with excellent yields. Copyright Taylor & Francis Group, LLC.
- Iranpoor, Nasser,Firouzabadi, Habib,Jamalian, Arezu
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p. 2615 - 2621
(2007/10/03)
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- Tribromoisocyanuric acid: A new reagent for regioselective cobromination of alkenes
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A simple one-step method for the preparation of tribromoisocyanuric acid in good yield (87%) has been developed. The reaction of tribromoisocyanuric acid with alkenes in presence of nucleophilic solvents (MeOH, i-PrOH, AcOH and a mixture of H2O-acetone, 1:5) led to the corresponding β-bromoethers, β-bromoacetates and bromohydrins, in high regioselectivity and good yields (73-98%). Georg Thieme Verlag Stuttgart.
- De Almeida, Leonardo S.,Esteves, Pierre M.,De Mattos, Marcio C. S.
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p. 1515 - 1518
(2007/10/03)
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- A simple and efficient method for regioselective and stereoselective synthesis of vicinal bromohydrins and alkoxybromides from an olefin
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(Chemical Equation Presented) A very rapid and efficient method has been developed for the synthesis of vicinal bromohydrins and alkoxybromides directly from an olefin without any catalyst. The reaction was performed in CH 3CN-water (4:1) or alcohol using N,N-dibromo-p-toluenesulfonamide (TsNBr2) as the brominating agent. Excellent yields and regio- and stereoselectivities have been obtained. Bromohydrins are formed instantaneously, whereas formation of alkoxybromides takes 30-60 min.
- Phukan, Prodeep,Chakraborty, Pranita,Kataki, Dolly
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p. 7533 - 7537
(2007/10/03)
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- Ionic liquid as reagent. A green procedure for the regioselective conversion of epoxides to vicinal-halohydrins using [AcMIm]X under catalyst- and solvent-free conditions
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A variety of structurally diverse epoxides undergo facile cleavages by ionic liquid, [AcMIm]X without any catalyst and solvent to produce the corresponding vicinal halohydrins in high yields. The cleavages are considerably fast and highly regioselective.
- Ranu, Brindaban C.,Banerjee, Subhash
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p. 4517 - 4519
(2007/10/03)
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- Green approach for the conversion of olefins into vic-halohydrins using N-halosuccinimides in ionic liquids
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Alkenes undergo smooth bromo- and iodohydroxylation with N-bromo- and N-iodosuccinimides/water, respectively, using the air and moisture stable ionic liquid [bmim]BF4 as a novel recyclable reaction medium in high to quantitative yields. N-Halosuccinimides show enhanced reactivity in ionic liquids thereby reducing the reaction times and improving the yields considerably.
- Yadav,Reddy,Baishya, Gakul,Harshavardhan,Janardhana Chary,Gupta, Manoj Kumar
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p. 3569 - 3572
(2007/10/03)
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- o-Phenylenediamine as a new catalyst in the highly regioselective conversion of epoxides to halohydrins with elemental halogens
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The regioselective ring opening of epoxides using elemental iodine and bromine in the presence of o-phenylenediamine as a new catalyst affords vicinal iodo alcohols and bromo alcohols in high yields. The major advantages of this method are versatility, high regioselectivity, a cheap and commercially available catalyst, mild and neutral reaction conditions, and short reaction times. Fourier transform Raman spectroscopy was used to study the reaction of iodine with o-phenylenediamine. The results indicate that the complex [(Diamine)I]+·I5- is formed, and we suggest that the major nucleophile is the pentaiodide ion. This bulky nucleophile has a fundamental role in the high regioselectivity observed attacking the less sterically hindered epoxide carbon. Springer-Verlag 2004.
- Eshghi, Hossein,Tayyari, Sayyed Faramarz,Sanchuli, Esmaiel
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p. 1101 - 1111
(2007/10/03)
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- Green protocol for the synthesis of vicinal-halohydrins from oxiranes using the [Bmim]PF6/LiX reagent system
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Epoxides undergo rapid ring-opening with lithium halides in [bmim]PF 6 or [bmim]BF4 ionic liquids under mild and neutral conditions to afford the corresponding vic-halohydrins in high to quantitative yields. The epoxides show enhanced reactivity in ionic liquids thereby reducing reaction times and improving the yields significantly. The recovered ionic liquid can be reused in three to four subsequent runs with consistent activity.
- Yadav,Reddy,Reddy, Ch. Srinivas,Rajasekhar
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p. 476 - 477
(2007/10/03)
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- Selective conversion of epoxides to vic-halo alcohols and symmetrical or unsymmetrical dihalides by triphenylphosphine/2,3-dichloro-5,6-dicyano-1,4- benzoquinone (DDQ) in the presence of quaternary ammonium halides
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A new method is described for the efficient and selective conversion of epoxides to vic-halo alcohols or symmetrical and unsymmetrical dihalides using PPh3/DDQ/R4NX (X = Cl, Br, I) as a mixed-reagent system.
- Iranpoor, Nasser,Firouzabadi, Habib,Aghapour, Ghasem,Nahid, Azarmidokht
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p. 1885 - 1891
(2007/10/03)
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- A General Route to the Synthesis of N-Protected 1-Substituted and 1,2-Disubstituted Taurines
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N-Benzyloxycarbonyl protected α-substituted and αβ- disubstituted taurines were synthesized from olefins and epoxides via N-benzyloxycarbonylamino alcohol thioacetates as key intermediates. They are important sulfur analogues of naturally occurring amino acids and building blocks for the synthesis of α-substituted and α,β- disubstituted β-sulfonopeptides.
- Xu, Jiaxi,Xu, Shu
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p. 276 - 282
(2007/10/03)
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- Micellar media for the efficient ring opening of epoxides with CN-, N3-, NO3-, NO2-, SCN-, Cl- and Br- catalyzed with Ce(OTf)4
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Micellar media are introduced for the efficient ring opening of epoxides with sodium salts of nucleophiles such as CN, N3-, NO3-, NO2, SCN, Br and Cl-, catalyzed with Ce(OTf)4. This method is an efficient procedure for the synthesis of different β-substituted alcohols under mild reaction conditions. The reaction with SCN- is an easy procedure for the high yielding preparation of epoxy sulfides.
- Iranpoor, Nasser,Firouzabadi, Habib,Shekarize, Marzieh
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p. 724 - 727
(2007/10/03)
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- Conversion of epoxides into halohydrins with elemental halogen catalyzed by thiourea
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A highly regioselective method for the synthesis of β-iodohydrins and β-bromohydrins by the direct ring opening of epoxides with elemental halogen in the presence of thiourea is described. This method occurs under neutral and mild conditions with high yields in various solvents even when sensitive functional groups are present.
- Sharghi, Hashem,Eskandari, Mohammad Mehdi
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p. 8509 - 8514
(2007/10/03)
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- Cleavage of epoxides into halohydrins with elemental iodine and bromine in the presence of 2,6-bis[2-(o-aminophenoxy)methyl]-4-bromo-1-methoxybenzene (BABMB) as catalyst
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The ring opening of epoxides with elemental iodine and bromine in the presence of 2,6-bis[2-(o-aminophenoxy)methyl]-4-bromo-1-methoxybenzene as a new catalyst affords vicinal iodo alcohols and bromo alcohols in high yields. This new procedure occurs regioselectively under neutral and mild conditions in various aprotic solvents even when sensitive functional groups are present.
- Niknam, Khodabakhsh,Nasehi, Taibeh
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p. 10259 - 10261
(2007/10/03)
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- Highly facile biomimetic regioselective ring opening of epoxides to halohydrins in the presence of β-cyclodextrin
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Highly regioselective ring opening of epoxides to halohydrins has been carried out in impressive yields with hydrogen and lithium halides in presence of β-cyclodextrin using water as solvent.
- Reddy, M.Arjun,Surendra,Bhanumathi,Rao, K.Rama
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p. 6003 - 6008
(2007/10/03)
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- Conversion of epoxides to halohydrins with elemental halogen catalyzed by phenylhydrazine
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The highly regioselective method for the synthesis of β-iodohydrins and β-bromohydrins by the direct ring opening of 1,2-epoxides with elemental halogen in the presence of phenylhydrazine is described. This method occurs under neutral and mild conditions with high yields in various aprotic solvents even when sensitive functional groups are present.
- Sharghi, Hashem,Eskandari, Mohammad Mehdi
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p. 1519 - 1522
(2007/10/03)
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- Dendrimeric organochalcogen catalysts for the activation of hydrogen peroxide: Improved catalytic activity through statistical effects and cooperativity in successive generations
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Dendrimeric polyphenylsulfides, -selenides, and -tellurides are prepared in high yield using propyloxy spacers to connect the phenylchalcogeno groups to the dendrimeric core. The selenides and tellurides catalyze the oxidation of bromide with hydrogen peroxide to give positive bromine species that can be captured by cyclohexene in two-phase systems. The corresponding sulfides show no catalytic activity. The increase in the rate of catalysis followed statistical effects for 1, 6, and 12 phenyltelluro groups. However, the increase in the rate of catalysis exceeds statistical contributions for the first few generations with 1, 3, 6, and 12 phenylseleno groups and suggested cooperativity among phenylseleno groups. The increase in catalytic rate was lost upon replacing all but one phenylseleno group with phenoxy groups. On the basis of H2O2 consumed, the dendrimer with 12 phenylseleno groups has a turnover number of >60 000 mol of H2O2 consumed per mole of catalyst.
- Francavilla,Drake,Bright,Detty
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- The halogen-mediated opening of epoxides in the presence of pyridine-containing macrocycles
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The ring opening of epoxides with elemental iodine and bromine in the presence of three pyridine-containing macrocyclic diamides as new catalysts affords vicinal iodo alcohols and bromo alcohols in high yields. This new procedure occurs regioselectively under mild conditions in various aprotic solvents. The catalysts are easily recovered and can be reused several times.
- Sharghi, Hashem,Niknam, Khodabakhsh,Pooyan, Maryam
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p. 6057 - 6064
(2007/10/03)
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- Interaction in trans-2-halocyclohexanols - An infrared and theoretical study
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The O - H and C - O stretching frequencies of trans-2-halocyclohexanols in CCl4 solutions have been measured and theoretical calculations have been performed to elucidate the main interactions, which are responsible for the conformational equil
- Freitas,Tormena,Rittner
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p. 175 - 180
(2007/10/03)
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- Observations on the use of triphenylphosphonium bromide as a mild and quantifiable source of hydrogen bromide for chemoselective ring opening of epoxides to bromohydrins
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The chemoselective ring opening of epoxides to bromohydrins in the presence of ketal, benzyloxymethoxy and trimethylsilyl ether functionality using triphenylphosphonium bromide is described. The preparation of a polymer supported variant is also reported.
- Afonso, Carlos A.M.,Vieira, Nuno M.L.,Motherwell, William B.
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p. 382 - 384
(2007/10/03)
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- Iron(III) trifluoroacetate as an efficient catalyst for solvolytic and nonsolvolytic nucleophilic ring opening of epoxides
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Iron(III) trifluoroacetate was used as an efficient and nonhygroscopic catalyst for the alcoholysis, hydrolysis, and acetolysis of epoxides. The addition of chloride, bromide, iodide, and nitrate ions to epoxides to produce the corresponding 2-halo and 2-nitratoalkanols and also the conversion of epoxides to acetonides and thiiranes were also performed efficiently in the presence of this catalyst.
- Iranpoor, Nasser,Adibi, Hadi
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p. 675 - 680
(2007/10/03)
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- Optical resolution of racemic alcohols via diastereoisomeric supramolecular compound formation with O,O'-dibenzoyl-(2R,3R)-tartaric acid
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O,O'-Dibenzoyl-(2R,3R)-tartaric acid (DBTA) forms a hydrogen bonded supramolecular compound with alcohols. The supra-molecular compound formation is enantioselective for a large number of chiral alcohols, therefore DBTA can be used as resolving agent, also for compounds having no basic group. The condition of the complex formation is that the guest molecule should contain a proton donating group and a fitting aliphatic chain or cycloalkane ring. (C) 2000 Elsevier Science Ltd.
- Kassai, Csaba,Juvancz, Zoltán,Bálint, József,Fogassy, Elemér,Kozma, Dávid
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p. 8355 - 8359
(2007/10/03)
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- Dendrimeric catalysts for the activation of hydrogen peroxide. Increasing activity per catalytic phenylseleno group in successive generations
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(matrix presented) Dendrimeric polyphenylselenides are prepared in high yield using propyloxy spacers to connect the phenyseleno groups to the dendrimeric core. The selenides catalyze the oxidation of bromide with hydrogen peroxide to give positive bromine species that can be captured by cyclohexene in two-phase systems. The increase in the rate of catalysis exceeds statistical contributions for the first few generations with 3, 6, and 12 phenylseleno groups.
- Francavilla, Charles,Bright, Frank V.,Detty, Michael R.
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p. 1043 - 1046
(2008/02/09)
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- Metalloporphyrins as New Catalysts in the Highly Regioselective Conversion of Epoxides to Halohydrins with Molecular Halogen
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The halogenative cleavage of epoxides occurs by addition of molecular iodine and bromine in the presence of catalytic amount of metalloporphyrins under mild conditions in various aprotic solvents. The corresponding vicinal iodohydrins and bromohydrins were obtained with highly regioselectivity in high yields.
- Sharghi, Hashem,Naeimi, Hossein
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p. 1357 - 1372
(2007/10/03)
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- Generation of interhalogen fluorides under mild conditions: A comparison of sluggish and reactive interhalogen fluorides
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Interhalogen fluorides (XF; X = I, Br, or Cl) generated from xenon difluoride (XeF2) or triethylamine trihydrofluoride (TREAT HF) with iodine (I2), N-halosuccinimides (NXS; X = I, Br, or Cl), or alkylhypohalites (ROX; R = CH3 or t-Bu, X = Br or Cl) with alkenes and aromatics are reported. A comparison of the above reactions with other methods reported in the literature to generate interhalogen fluorides is made. Interhalogens generated from direct action of elemental fluorine (F2) or XF3 (X = I, Br, or Cl) with chlorine (Cl2), bromine (Br2), or iodine (I2) give a species that can react with electron-deficient alkenes or aromatics. These reagents are too reactive for electron-rich substrates. Interhalogen fluorides from reagents like NXS or ROX with XeF2 or amine HF are much less reactive and give good yields with electron-rich akenes or aromatics.
- Shellhamer, Dale F.,Horney, Mark J.,Pettus, Benjamin J.,Pettus, Tobiah L.,Stringer, Joy Merry,Heasley, Victor L.,Syvret, Robert G.,Dobrolsky Jr., John M.
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p. 1094 - 1098
(2007/10/03)
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- Efficient, mild and highly regioselective cleavage of epoxides with elemental halogen catalyzed by 2-phenyl-2-(2-pyridyl)imidazolidine(PPI)
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The highly regioselective conversion of epoxides into corresponding vicinal halohydrins with elemental halogen are catalyzed by imidazolidine derivative. This method occurs under neutral and mild conditions with high yields in various aprotic solvents even when sensitive functional groups are present.
- Sharghi, Hashem,Naeimi, Hossein
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p. 1343 - 1344
(2007/10/03)
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- Solvent-free organic reactions on silica gel supports. Facile transformation of epoxides to β-halohydrins with lithium halides
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The reaction of epoxides with lithium halides was efficiently promoted on the surface of silica gel in the absence of any solvent to give the corresponding β-halohydrins. The reactivity of lithium halides was shown to follow the order LiI > LiBr >> LiCl, and the reactivity of LiCl was dramatically increased by adding an equivalent amount of water to this system. On the other hand a similar reaction with α,β-epoxyketones produces the α-haloenone derivatives, presumably via halohydrin intermediates. The epoxide-opening reaction of (R)-(+)-styrene oxide was also investigated to clarify the stereochemical features of this reaction.
- Kotsuki, Hiyoshizo,Shimanouchi, Tomoyasu,Ohshima, Reiji,Fujiwara, Shunsuke
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p. 2709 - 2722
(2007/10/03)
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- Crown Ethers as New Catalysts in the Highly Regioselective Halogenative Cleavage of Epoxides with Elemental Halogen
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The regioselective ring opening halogenation of some epoxides using elemental iodine and bromine in the presence of a series of new synthetic macrocycle diamides and also dibenzo-18-crown -6, 18-crown-6, and aza-18-crown-6 has been studied. The epoxides were subject to cleavage by elemental halogen (I2 and Br2) in the presence of these catalysts under mild reaction conditions in various aprotic solvents. In this study, reagents and conditions have been discovered with which the individual halohydrins can be synthesized in high yield and with more than 95% regioselectivity. The results can be discussed in terms of a four-step mechanism: (1) formation of a charge-transfer complex between catalyst and halogen, (2) release of halogen nucleophile from the complex, (3) reaction of the active nucleophile at the less sterically-hindered site in the epoxide, and (4) regeneration of catalyst. The major advantages of this method are high regioselectivity, simple regeneration of catalyst and its reuse through several cycles without a decrease in activity, and ease of workup of the reaction.
- Sharghi, Hashem,Massah, Ahmad Reza,Eshghi, Hossein,Niknam, Khodabakhsh
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p. 1455 - 1461
(2007/10/03)
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- Highly regio- and stereoselective synthesis of β-halohydrins from epoxides catalyzed with ceric ammonium nitrate
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Ce(IV) as ceric ammonium nitrate can effectively catalyze ring opening of epoxides with halides under very mild conditions and easy procedure to give the corresponding β-chloro- and β-bromohydrins in excellent yields. The reactions occur with both substituted and unsubstituted quaternary ammonium halides and with high regio- and stereoselectivity. The reaction of optically active styrene oxide with chloride ion was found to be highly stereospecific and afforded the corresponding β-halohydrin in 96% ee.
- Iranpoor,Kazemi,Salehi
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p. 1247 - 1258
(2007/10/03)
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- FeCl3·6H2O supported on SiO2 catalysed ring opening of epoxides with alcohols, acetic acid, water, chloride, bromide and nitrate ions
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FeCl3·6H2O absorbed on chromatographic silica gel can act as an efficient catalyst for alcoholysis, hydrolysis and acetolysis of epoxides. Methanolysis of (R)-styrene oxide proceeds with high stereospecificity and in excellent yield. This catalyst can also convert epoxides to their corresponding β-halohydrins and β-nitrato alcohols in the presence of chloride, bromide and nitrate ions respectively.
- Iranpoor, Nasser,Tarrian, Tahere,Movahedi, Zarangiz
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p. 1473 - 1476
(2007/10/03)
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