- Iridium-catalyzed efficient reduction of ketones in water with formic acid as a hydride donor at low catalyst loading
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A highly efficient and chemoselective transfer hydrogenation of ketones in water has been successfully achieved with our newly developed catalyst. Simple ketones, as well as α- or β-functionalized ketones, are readily reduced. Formic acid is used as a traceless hydride source. At very low catalyst loading (S/C = 10:000 in most cases; S/C = 50:000 or 100:000 in some cases), the iridium catalyst is impressively efficient at reducing ketones in good to excellent yields. The TOF value can be as high as up to 26:000 mol mol-1 h-1. A variety of functional groups are well tolerated, for example, heteroaryl, aryloxy, alkyloxy, halogen, cyano, nitro, ester, especially acidic methylene, phenol and carboxylic acid groups.
- Liu, Ji-Tian,Yang, Shiyi,Tang, Weiping,Yang, Zhanhui,Xu, Jiaxi
-
supporting information
p. 2118 - 2124
(2018/05/24)
-
- Extreme halophilic alcohol dehydrogenase mediated highly efficient syntheses of enantiopure aromatic alcohols
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Enzymatic synthesis of enantiopure aromatic secondary alcohols (including substituted, hetero-aromatic and bicyclic structures) was carried out using halophilic alcohol dehydrogenase ADH2 from Haloferax volcanii (HvADH2). This enzyme showed an unprecedented substrate scope and absolute enatioselectivity. The cofactor NADPH was used catalytically and regenerated in situ by the biocatalyst, in the presence of 5% ethanol. The efficiency of HvADH2 for the conversion of aromatic ketones was markedly influenced by the steric and electronic factors as well as the solubility of ketones in the reaction medium. Furthermore, carbonyl stretching band frequencies ν (CO) have been measured for different ketones to understand the effect of electron withdrawing or donating properties of the ketone substituents on the reaction rate catalyzed by HvADH2. Good correlation was observed between ν (CO) of methyl aryl-ketones and the reaction rate catalyzed by HvADH2. The enzyme catalyzed the reductions of ketone substrates on the preparative scale, demonstrating that HvADH2 would be a valuable biocatalyst for the preparation of chiral aromatic alcohols of pharmaceutical interest.
- Alsafadi, Diya,Alsalman, Safaa,Paradisi, Francesca
-
p. 9169 - 9175
(2017/11/15)
-
- Exploiting a beast in carbenoid chemistry: Development of a straightforward direct nucleophilic fluoromethylation strategy
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The first direct and straightforward nucleophilic fluoromethylation of organic compounds is reported. The tactic employs a fleeting lithium fluorocarbenoid (LiCH2F) generated from commercially available fluoroiodomethane. Precise reaction conditions were developed for the generation and synthetic exploitation of such a labile species. The versatility of the strategy is showcased in ca. 50 examples involving a plethora of electrophiles. Highly valuable chemicals such as fluoroalcohols, fluoroamines, and fluoromethylated oxygenated heterocycles could be prepared in very good yields through a single synthetic operation. The scalability of the reaction and its application to complex molecular architectures (e.g., steroids) are documented.
- Parisi, Giovanna,Colella, Marco,Monticelli, Serena,Romanazzi, Giuseppe,Holzer, Wolfgang,Langer, Thierry,Degennaro, Leonardo,Pace, Vittorio,Luisi, Renzo
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supporting information
p. 13648 - 13651
(2017/11/06)
-
- Versatile iridicycle catalysts for highly efficient and chemoselective transfer hydrogenation of carbonyl compounds in water
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Cyclometalated iridium complexes are shown to be highly efficient and chemoselective catalysts for the transfer hydrogenation of a wide range of carbonyl groups with formic acid in water. Examples include α-substituted ketones (α-ether, α-halo, α-hydroxy, α-amino, α-nitrile or α-ester), α-keto esters, β-keto esters and α,β-unsaturated aldehydes. The reduction was carried out at substrate/catalyst ratios of up to 50000 at pH 4.5 and required no organic solvent. The protocol provides a practical, easy and efficient way for the synthesis of β-functionalised secondary alcohols, such as β-hydroxyethers, β-hydroxyamines and β-hydroxyhalo compounds, which are valuable intermediates in pharmaceutical, fine chemical, perfume and agrochemical synthesis. Water wonder: Iridicycle catalysts are versatile and allow the highly efficient and chemoselective transfer hydrogenation of a variety of carbonyl compounds, including problematic and challenging ones, with formate in neat water (see scheme).
- Talwar, Dinesh,Wu, Xiaofeng,Saidi, Ourida,Salguero, Noemí Poyatos,Xiao, Jianliang
-
supporting information
p. 12835 - 12842
(2015/03/30)
-
- Steric vs. electronic effects in the Lactobacillus brevis ADH-catalyzed bioreduction of ketones
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Lactobacillus brevis ADH (LBADH) is an alcohol dehydrogenase that is commonly employed to reduce alkyl or aryl ketones usually bearing a methyl, an ethyl or a chloromethyl as a small ketone substituent to the corresponding (R)-alcohols. Herein we have tested a series of 24 acetophenone derivatives differing in their size and electronic properties for their reduction employing LBADH. After plotting the relative activity against the measured substrate volumes we observed that apart from the substrate size other effects must be responsible for the activity obtained. Compared to acetophenone (100% relative activity), other small substrates such as propiophenone, α,α, α-trifluoroacetophenone, α-hydroxyacetophenone, and benzoylacetonitrile had relative activities lower than 30%, while medium-sized ketones such as α-bromo-, α,α-dichloro-, and α,α-dibromoacetophenone presented relative activities between 70% and 550%. Moreover, the comparison between the enzymatic activity and the obtained final conversions using an excess or just 2.5 equiv. of the hydrogen donor 2-propanol, denoted again deviations between them. These data supported that these hydrogen transfer (HT) transformations are mainly thermodynamically controlled. For instance, bulky α-halogenated derivatives could be quantitatively reduced by LBADH even employing 2.5 equiv. of 2-propanol independently of their kinetic values. Finally, we found good correlations between the IR absorption band of the carbonyl groups and the degrees of conversion obtained in these HT processes, making this simple method a convenient tool to predict the success of these transformations. The Royal Society of Chemistry.
- Rodriguez, Cristina,Borzecka, Wioleta,Sattler, Johann H.,Kroutil, Wolfgang,Lavandera, Ivan,Gotor, Vicente
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supporting information
p. 673 - 681
(2014/01/06)
-
- On the configurational stability of chiral, nonracemic fluoro- and iodo-[D1]methyllithiums
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Enantiomerically pure fluoro-[D1]methyllithium and iodo-[D 1]methyllithiums of up to 92% ee were generated by transmetalation of the corresponding stannanes with MeLi in THF at various temperatures. The intermediate halo-[D1]methyllithiums were trapped with benzaldehyde or acetophenone already present in excess in the reaction mixture to either give halohydrins or to disintegrate to carbene. The fluoro-[D1] methyllithiums were found to be microscopically configurationally stable within the tested range of -95 to 0°C, but chemically only stable at temperatures below -95°C due to a rapidly increasing portion disintegrating to carbene. The iodo-[D1]methyllithiums were configurationally labile relative to the rate of addition to PhCHO at all temperatures tested (-95 to -30°C). Disintegration to carbene interfered as well. The microscopic configurational stability of enantiomerically pure fluoro-[D1]methyllithiums prepared by tin-lithium exchange in the presence of excess benzaldehyde or acetophenone has been investigated. Depending on the reaction temperature, a portion of the generated fluoro-[D1]methyllithiums was added to the electrophiles to give fluorohydrins; the remaining portions disintegrated to carbene and LiF (see scheme).
- Kail, Dagmar C.,Malova Krizkova, Petra,Wieczorek, Anna,Hammerschmidt, Friedrich
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p. 4086 - 4091
(2014/04/17)
-
- Synthesis of enantiopure fluorohydrins using alcohol dehydrogenases at high substrate concentrations
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The use of purified and overexpressed alcohol dehydrogenases to synthesize enantiopure fluorinated alcohols is shown. When the bioreductions were performed with ADH-A from Rhodococcus ruber overexpressed in E. coli, no external cofactor was necessary to obtain the enantiopure (R)-derivatives. Employing Lactobacillus brevis ADH, it was possible to achieve the synthesis of enantiopure (S)-fluorohydrins at a 0.5 M substrate concentration. Furthermore, due to the activated character of these substrates, a huge excess of the hydrogen donor was not necessary.
- Borzeicka, Wioleta,Lavandera, Ivan,Gotor, Vicente
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p. 7312 - 7317
(2013/08/23)
-
- Solvent selection in synthesis of 4-(1-arylfluoroethoxy)quinazolines and thienopyrimidines
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The nucleophilic aromatic substitution of 4-chloroquinazoline and 6-bromo-4-chlorothieno[2,3-d]pyrimidine with 1-aryl-2-fluoroethanols as nucleophilies has been studied focusing on the use of carbonate bases in combination of environmental acceptable solvents. The conversion rate depended on the solvent properties, the acidity of the nucleophile and the nature of the base. By using acetonitrile as reaction medium and K2CO3 as base, 2,2,2-trifluoro-, 2,2-difluoro-, and 2-fluoro-1-phenylethanol could efficiently be coupled to 4-chloropyrimidines. Alternatively, employing Cs 2CO3, allowed for shorter reaction time for these substrates, and also couplings of the non-fluorinated alcohols proceeded well. tert-Butanol was also found to be a suitable reaction medium in transformation of the fluoro alcohols. Testing of hydrolytic stability of the 4-alkoxypyrimidines revealed that the fluorinated and nonfluorinated derivatives were labile under acidic conditions, whereas in basic media the fluoroalkoxy derivatives were more stable than their non-fluorinated counterparts.
- Han, Jin,Sundby, Eirik,Hoff, B?ge H.
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supporting information
p. 82 - 88
(2013/11/06)
-
- Palladium-catalyzed intermolecular fluoroesterification of styrenes: Exploration and mechanistic insight
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A novel palladium-catalyzed intermolecular oxidative fluoroesterification of vinylarenes has been developed using NFSI, one of the mildest electrophilic fluorinating reagents. The reaction presents an efficient synthetic pathway to afford a series of α-monofluoromethylbenzyl carboxylates in good to excellent yields. Rather than following an electrophilic fluorination pathway, the reaction is initiated through oxidation of Pd(0) to a Pd(ii) fluoride complex by NFSI, followed by fluoropalladation of a styrene to generate an α-monofluoromethylbenzyl-Pd intermediate. Generally, reductive elimination of benzyl-PdII complexes is favored with relatively strong oxy-nucleophiles to afford C-O bonds. This reaction, however, exhibited the opposite reactivity: strong acids with weak nucleophilicity, such as CF 3CO2H and CCl3CO2H, were prone to afford the fluoroesterification product, while weak acids with strong nucleophilicity, such as HOAc and BzOH, did not deliver the C-O bond product. Further mechanistic studies determined that Csp3-Pd(O2CR), a key intermediate, was generated through ionic ligand exchange between benzyl-Pd(NZ2) and CF3CO2H, and the final C-O bond was possibly formed through reductive elimination of a high-valent Csp 3-Pd(O2CR) complex via an SN2-type nucleophilic attack pathway.
- Peng, Haihui,Yuan, Zheliang,Wang, Hao-Yang,Guo, Yin-Long,Liu, Guosheng
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p. 3172 - 3178
(2013/07/26)
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- Microwave assisted fluorofunctionalization of phenyl substituted alkenes using selectfluor
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A rapid fluorofunctionalization of alkenes and diene using selectfluor has been uncovered. The olefins such as 1-phenyl ethene; 1,1-diphenylethene; (E)-1,2-diphenylethene; (E)-1,2-dinaphthylethene; 1,1,2-triphenylethene; 1,1,2,2-tetraphenylethene and 1,1,
- Kumar, Anil,Singh, Tej Vir,Venugopalan, Paloth
-
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- Alpha selective epoxide opening with 18F-: Synthesis of 4-(3-[18F]fluoro-2-hydroxypropoxy)benzaldehyde ([ 18F]FPB) for peptide labeling
-
Strained tricyclic ring systems such as epoxides are rarely used as precursors for the introduction of anionic fluorine-18 into organic compounds intended for positron emission tomography (PET). Here we report the alpha selective ring opening of epoxides
- Schirrmacher, Ralf,Lucas, Philippe,Schirrmacher, Esther,W?ngler, Bj?rn,W?ngler, Carmen
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scheme or table
p. 1973 - 1976
(2011/04/25)
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- Asymmetric reduction using (R)-MeCBS and determination of absolute configuration of para-substituted 2-fluoroarylethanols
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The asymmetric reduction of eight α-fluoroacetophenones has been investigated using (R)-MeCBS as a catalyst in various media. Based on a solvent screen, 1,2-dimethoxyethane, diethyl ether and dichloromethane were used in reductions of the α-fluoroacetophe
- Fuglseth, Erik,Sundby, Eirik,Bruheim, Per,Hoff, Bard Helge
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p. 1941 - 1946
(2008/12/22)
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- Anhydrous flouride salts and reagents and methods for their production
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Anhydrous organic fluoride salts and reagents prepared by a method comprising the nucleophilic substitution of a fluorinated aromatic or fluorinated unsaturated organic compound with a salt having the formula: [QnM]x+Ax?in an inert polar, aprotic solvent; wherein M is an atom capable of supporting a formal positive charge, the n groups Q are independently varied organic moieties, n is an integer such that the [QnM] carries at least one formal positive charge, x is an integer defining the number of formal positive charge(s), +, carried by the [QnM], A? is an anionic nucleophile capable of substituting for F in the fluorinated compound and F represents fluorine or a radioisotope thereof.
- -
-
Page/Page column 5-6
(2008/06/13)
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- Anhydrous tetrabutylammonium fluoride
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Tetrabutylammonium fluoride (TBAF) is prepared at low temperature by nucleophilic aromatic substitution of hexafluorobenzene with tetrabutylammonium cyanide. Adventitious water is scavenged during this synthesis by the generated hexacyanobenzene, which readily adds water under basic conditions. Contrary to expectations, TBAF is stable to Hofmann elimination in polar aprotic solvents under anhydrous conditions. Added hydroxylic solvents are shown to catalyze the decomposition of TBAF and to catalyze proton exchange with DMSO. The synthetic utility of this salt is described briefly. Copyright
- Sun, Haoran,DiMagno, Stephen G.
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p. 2050 - 2051
(2007/10/03)
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- The role of organic fluorine in directing alkylation reactions via lithium chelation
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The fluorine of a fluoromethyl group displays a measurable chelation effect to lithium during α-methylation of an ester with lithium diisopropylamide (LDA) and methyl iodide. A series of esters is compared with F, H and O, and the resultant diastereoselectivity is consistent with the intermediate capacity of F to chelate lithium relative to H and O. In a second system which involved comparing a tertiary organic fluorine with hydrogen, no such effect is apparent, most probably due to adverse steric effects. The absolute and relative stereochemistry of the predominant diastereoisomers are confirmed by X-ray crystallography of suitable crystalline derivatives in each case. It is concluded that there is a potential role for organic-bound fluorine to become involved in lithium chelation in well-designed enolate alkylation systems. The diastereoselectivity of alkylation is explored comparing the coordination ability of H, F and OR substituents in the above model.
- Tenza, Kenny,Northen, Julian S.,O'Hagan, David,Slawin, Alexandra M.Z.
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p. 1779 - 1790
(2007/10/03)
-
- Selective and effective fluorination of organic compounds in water using selectfluor F-TEDA-BF4
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(Chemical Equation Presented) Selective and effective fluorination of various types of organic compounds performed in water as the reaction medium using 1-chloromethyl-4-fluoro-1,4-diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate) (Selectfluor F-TEDA-BF
- Stavber, Gaj,Zupan, Marko,Jereb, Marjan,Stavber, Stojan
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p. 4973 - 4976
(2007/10/03)
-
- Regioselective synthesis of fluorohydrines via SN2-type ring-opening of epoxides with TBABF-KHF2
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We found that the ring-opening fluorination of terminal epoxides using TBABF-KHF2 proceeds with high selectivity through the SN2 mechanism. As TBABF-KHF2 is easily obtainable, is stable, and can be used in glassware, it ca
- Akiyama, Yuriko,Fukuhara, Tsuyoshi,Hara, Shoji
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p. 1530 - 1532
(2007/10/03)
-
- Regioselective, stereospecific, and chemoselective fluorination of epoxy alcohols: Development of fluorinating hybrid reagents, associated with Lewis acid metal fluoride/ammonium hydrogen fluoride
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A new type of fluorinating reagent of Lewis acid metal fluoride/ammonium hydrogen fluoride is developed for regio-, stereo-, and chemoselective ring opening fluorination of epoxy alcohols.
- Mikami, Koichi,Ohba, Shiho,Ohmura, Hirofumi
-
-
- Activation of pig liver esterase in organic media with organic polymers. Application to the enantioselective acylation of racemic functionalized secondary alcohols
-
Pig liver esterase (PLE) shows practically no activity in acylation of alcohols with vinylic esters in organic solvents. However, addition of methoxypoly(ethylene glycol) (MPEG), bovine serum albumin (BSA), TentaGelAmino resin (TGA), or aminomethyl polystyrene (AMPS) confers activity to PLE in acylation of alcohols with vinyl propionate in organic solvents of low water content. Polymer-activated PLE showed high enantioselectivities (E > 100) in the acylation of racemic 1-alkoxy-, 1-ethylsulfanyl-, and 1-fluoro-3-aryl-2-propanols as well as racemic 1-phenoxy-2-propanol and racemic 1-methoxy-2-phenoxy-2-propanol. The synthetic utility of polymer-activated PLE has been demonstrated by the gram-scale resolution of 1-methoxy-3-phenyl-2-propanol, 1-ethylsulfanyl-3-phenyl-2-propanol, 1-methoxy-3-p-methoxyphenyl-2-propanol, 1- fluoro-3-phenyl-2-propanol, and 1-methoxy-3-phenoxy-2-propanol. In PLE-catalyzed acylation of alcohols with vinyl propionate, acetaldehyde and propionic acids, both being detrimental to the enzyme, are formed as byproducts. In addition, the water content of the system, which is critical for the activity of pig liver esterase, is lowered because of a competing enzymatic hydrolysis of the acyl donor. The polymers TGA, BSA, and AMPS not only scavenge the aldehyde and the acid through imine formation and neutralization, respectively, but replenish at least in part also the water consumed in the competing hydrolysis of the acyl donor. A recovery of PLE together with the polymer was achieved without major loss of activity through their immobilization on a water-saturated polyaramide membrane, which occurs spontaneously in organic solvents.
- Gais,Jungen,Jadhav
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p. 3384 - 3396
(2007/10/03)
-
- Effect of reaction conditions on the kinetic and activation parameters for the mild introduction of fluorine into α-substituted styrenes with AccufluorTM NFTh
-
Kinetic studies on fluorination of α-substituted styrenes with 1-fluoro-4-hydroxy-1,4-diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate) (AccufluorTM NFTh) in acetonitrile or in acetonitrile in the presence of methanol or water as nucleophiles were carried out. These reactions exhibited overall second-order kinetics and formed Markovnikov type products. The corresponding second-order rate constants for fluorination of the studied substrates in the presence of methanol at 38.8 deg C are k2 = 1.1 x 10-3 M-1 s-1 for styrene (1a), 3.3 x 10-2 M-1 s-1 for α-methylstyrene (1b) and 3.4 x 10-2 M-1 s-1 for 1,1-diphenylethene (1c). The substitution of methanol as nucleophile by water had very little effect on the rate of the process. Solvent polarity variation (Grunwald-Winstein Ybenzyl) showed a similar small effect, too, indicating negligible change in the polarity of the rate-determining transition state in comparison with the reactants. Activation enthalpies (between 62 and 80 kJ mol-1) and activation antropies (between -74 and 32 J mol-1 K-1) were determined for fluorination of α-substituted styrenes with NFTh in acetonitrile in the presence of methanol and water as nucleophiles. Hammett correlation analysis of the reaction of substituted styrenes with NFTh in MeCN MeCN-H2O and MeCN-MeOH gave reaction constants ρ+ of -1.48, -1.52 and -1.80, respectively, which support our belief in the mainly non-polar character of the rate-determining transition state of the studied reactions.
- Stavber, Stojan,Pecan, Tjasa Sotler,Zupan, Marko
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p. 1141 - 1146
(2007/10/03)
-
- A unique chelating effect of Sc(OTf)3 to organofluorine compounds
-
The scandium trifluoromethanesulfonate-catalyzed cleavage of acetate bearing two or three fluorine atoms at a position β to an acetoxy group proceeds exceptionally rapidly. The high efficiency of the hydrolysis is caused by a chelating effect of scandium with the fluorine atoms and an acetate moiety.
- Kajiro, Hiroshi,Mori, Atsunori,Nishihara, Yasushi,Hiyama, Tamejiro
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p. 459 - 460
(2007/10/03)
-
- Use of kinetic isotope effects in mechanism studies. Isotope effects and element effects associated with Hydron-Transfer steps during alkoxide-promoted dehydrohalogenations
-
The Arrhenius behavior of the primary kinetic isotope effect, (k(H)/k(D))(Obs) and (k(H)/k(T))(Obs), associated with the methanolic sodium methoxide-promoted dehydrohalogenations of m-ClC6H4C(i)HClCH2Cl (I), m-CF3C6H4C(i)-HClCH2Cl (II) and p-CF3C6H4C(i)HClCH2F (III) has been used to calculate the internal-return parameters, a = k(-1)/K(Elim)(X), in a two-step mechanism featuring a hydrogen-bonded carbanion. This carbanion partitions between returning the hydron to carbon, k(-1), and the loss of halide, K(Elm)(X). Isotope effects at 25°C for I, (k(H)/k(D))(Obs) = 3.40 and (k(H)/ k(T))(Obs) = 6.20, and II, (k(H)/k(D))(Obs) = 3.49 and (k(H)/k(T))(Obs) = 6.55, result in similar values for a: a(H) = 0.59, a(D) = 0.13-0.14 and a(T) = 0.07. Smaller values of (k(H)/k(D))(Obs) = 2.19 and (k(H)/k(T))(Obs) = 3.56 for III are due to more internal return [a(H) = 1.9, a(D) = 0.50, and a(T) = 0.28] associated with the dehydrofluorination reaction. Calculation of k1 ( k(Obs) [a + 1]) results in similar isotope effects for hydron transfer in these reactions: k1(H)/k1(D) = 4.74 and k1(H)/K1(T) = 9.20; II, k1(H)/k1(D) = 4.91 and k1(H)/k1(T) = 9.75; III, k1(H)/k1(D) = 4.75 and k1(H)/k1(T) = 9.17. Reactions of m-ClC6H4C(i)HBrCH2Br and m-ClC6H4C(i)HClCH2Br have very small amounts of internal return, a(H) = 0.05 and a(D) = 0.01, and (k(H)/k(D))(Obs) = 4.95 results in k1(H)/k1(D) = 5.11 The measured isotope effects are therefore due to differences in the amount of internal return and not in the symmetry of transition state structures for the hydron transfer, and the element effect, (k(HBr)/ k(HCl)) = 29, for m-ClC6H4CHClCH2X is mainly due to the hydron-transfer step, k1(HBr)/k1(HCl) = 19, and not the breaking of the C-X bend. The kinetic solvent isotope effects, k(MeOD)/k(MeOH) ~ 2.5, are consistent with three methanols of solvation lost prior to the hydron-transfer step. The energetics associated with desolvation of methoxide ion are part of the measured reaction energetics of these systems.
- Koch, Heinz F.,Lodder, Gerrit,Koch, Judith G.,Bogdan, David J.,Brown, Geoffrey H.,Carlson, Carrie A.,Dean, Amy B.,Hage, Ronald,Han, Patrick,Hopman, Johan C. P.,James, Lisa A.,Knape, Petra M.,Roos, Eric C.,Sardina, Melissa L.,Sawyer, Rachael A.,Scott, Barbara O.,Testa III, Charles A.,Wickham, Steven D.
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p. 9965 - 9974
(2007/10/03)
-
- 1-Fluoro-4-hydroxy-1,4-diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate) as a new, effective reagent for selective fluorofunctionalisation of alkenes under mild reaction conditions
-
1-Fluoro-4-hydroxy-1,4-diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate) Accufluor NFTh) is confirmed as a highly effective reagent for introducing a fluorine atom into organic molecules across a phenyl-substituted carbon-carbon double bond. Quantitativ
- Stavber, Stojan
-
p. 6769 - 6772
(2007/10/02)
-
- Site-Selective Fluorination of Organic Compounds Using 1-Alkyl-4-fluoro-1,4-diazabicyclooctane Salts (Selectfluor Reagents)
-
The new "N-F"-type electrophilic reagent family of 1-alkyl-4-fluoro-1,4-diazabicyclooctane salts (derived from elemental fluorine (F2) and 1-alkyl-1,4-diazabicyclooctane salts) has been found to be very effective for the fluorination of a wide variety of organic substrates.These include steroidal enol acetates and silyl enol ethers, phenyl-substituted olefins, sulfides bearing α-H atoms, certain carbanions, and mildly activated aromatic compounds.The products were obtained with good yields and regioselectivity under very mild reaction conditions.
- Lal, G. Sankar
-
p. 2791 - 2796
(2007/10/02)
-
- N-Fluorobisimides: Reactions with Some Olefins via α-Fluoro Carbocationic Intermediates
-
N-Fluorobisimides are a new class of electrophilic fluorinating agents.Reaction of (CF3SO2)2NF (1) with olefins gave various products, depending on the reaction conditions and the structure of the substrate.In solvents of higher nucleophilicity such as H2O, acetic acid, aqueous HCl, and (HF)nPy, α-fluorohydrins and their acetates, α,β-chlorofluoro- and α,β-difluoroalkanes were obtained.In acetic acid, trans-stilbene and tetraphenylethylene produced the rearranged, nonfluorinated aldehyde and ketone.Evidence is presented for the reactions proceeding via a one-electron transfer mechanism involving α-fluorocarbocationic intermediates.
- DesMarteau, Darryl D.,Xu, Ze-Qi,Witz, Michael
-
p. 629 - 635
(2007/10/02)
-
- TETRABUTYLAMMONIUM DIHYDROGENTRIFLUORIDE: AN EFFICIENT CATALYST FOR REGIO AND STEREOSELECTIVE CONVERSION OF EPOXIDES TO FLUOROHYDRINS UNDER SOLID-LIQUID PHASE-TRANSFER CATALYSIS CONDITIONS.
-
Tetrabutylammonium dihydrogentrifluoride is an efficient and easy-to-handle hydrofluorating agent in the ring-opening reaction of oxiranes to give good or excellent yields of fluorohydrins under solid-liquid PTC conditions.
- Landini, Dario,Penso, Michele
-
p. 7209 - 7212
(2007/10/02)
-
- On the Mechanism of Reduction by Reduced Nicotinamide Adenine Dinucleotide Dependent Alcohol Dehydrogenase. α-Halo Ketones as Mechanistic Probes
-
α-Haloacetophenones have been used as mechanistic probes for the enzyme (HLADH) controlled reductions by NADH.The cofactor, NADH, itself reduced the α-haloacetophenones and yielded the product diagnostic of free radical reduction, acetophenone.In the presence of NADH/HLADH both the α-fluoro- and α-chloroacetophenones, although they were only slightly reactive with NADH, yielded the hydride reduction products, optically active 1-phenyl-2-haloethanol.The more reactive α-bromoacetophenone was reduced by a radical chain process, which did not involve the enzyme.Ahalo ketone of intermediate reactivity, α,α-dichloroacetophenone, was reduced by the enzyme to give the products of heterolytic reduction.The suitability of the α-haloacetophenones as diagnostic mechanistic probes for enzyme reactivity and of dihydropyridines as NADH/HLADH models is discussed.
- Tanner, Dennis D.,Stein, A. R.
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p. 1642 - 1646
(2007/10/02)
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- The reinvestigation of the kinetics of the reactions of fluorodi(4-nitrophenyl)ethanes with sodium methoxide in methanol
-
The procedure previously described for the preparation of 1-fluoro-2,2-di(4-nitrophenyl)ethane actually yields 1,1,2-tri(4-nitrophenyl)ethane.Fluoro-2,2-di(4-nitrophenyl)ethane has been prepared and rate constants, isotope effects, and activation parameters for the β-elimination reaction with methoxide ion in methanol are reported.These parameters indicate a concerted E2 mechanism, with a fairly symmetrical transition state.The subsequent dimerization reaction of the olefin product to yield 1,1,3,3-tetra(4-nitrophenyl)butene-1 is described.The reaction of 1,1,1-trifluoro-2,2-di(4-nitrophenyl)ethane with methoxide ion in methanol has been reinvestigated and the reaction on the first product 1,1-difluoro-2,2-di(4-nitrophenyl)ethylene with excess methoxide, to give di(4-nitrophenyl)ketene dimethylacetal in a multistep reaction, is reported.
- Leffek, Kenneth T.,Schroeder, Grzegorz
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p. 1696 - 1701
(2007/10/02)
-