- Decarboxylative Bromination of Sterically Hindered Carboxylic Acids with Hypervalent Iodine(III) Reagents
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Sterically hindered three-dimensional (3D) alkyl halides are promising precursors for various reactions; however, they are difficult to synthesize via conventional reactions. We present an efficient and practical method for decarboxylative bromination of sterically hindered 3D aliphatic carboxylic acids using commercially available (diacetoxyiodo)benzene and potassium bromide, one of the most stable and cheapest bromine sources in nature. The present method features a metal-free/Br2-free system, mild reaction conditions, one-pot operation under air at room temperature, wide functional group compatibility, and gram-scale synthetic capability. This highly efficient reaction cleanly converts a broad range of carboxylic acids, the most inexpensive and readily available sources of highly strained/naturally occurring/drug-related scaffolds, into the corresponding alkyl bromides in good to high yields.
- Kanazawa, Junichiro,Koyamada, Kenta,Miyamoto, Kazunori,Uchiyama, Masanobu,Watanabe, Ayumi
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supporting information
p. 1328 - 1334
(2020/08/14)
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- Highly selective halogenation of unactivated C(sp3)-H with NaX under co-catalysis of visible light and Ag@AgX
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The direct selective halogenation of unactivated C(sp3)-H bonds into C-halogen bonds was achieved using a nano Ag/AgCl catalyst at RT under visible light or LED irradiation in the presence of an aqueous solution of NaX/HX as a halide source, in air. The halogenation of hydrocarbons provided mono-halide substituted products with 95% selectivity and yields higher than 90%, with the chlorination of toluene being 81%, far higher than the 40% conversion using dichlorine. Mechanistic studies demonstrated that the reaction is a free radical process using blue light (450-500 nm), with visible light being the most effective light source. Irradiation is proposed to cause AgCl bonding electrons to become excited and electron transfer from chloride ions induces chlorine radical formation which drives the substitution reaction. The reaction provides a potentially valuable method for the direct chlorination of saturated hydrocarbons.
- Liu, Shouxin,Zhang, Qi,Tian, Xia,Fan, Shiming,Huang, Jing,Whiting, Andrew
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p. 4729 - 4737
(2018/10/23)
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- Selective C-H halogenation over hydroxylation by non-heme iron(iv)-oxo
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Non-heme iron based halogenase enzymes promote selective halogenation of the sp3-C-H bond through iron(iv)-oxo-halide active species. During halogenation, competitive hydroxylation can be prevented completely in enzymatic systems. However, synthetic iron(iv)-oxo-halide intermediates often result in a mixture of halogenation and hydroxylation products. In this report, we have developed a new synthetic strategy by employing non-heme iron based complexes for selective sp3-C-H halogenation by overriding hydroxylation. A room temperature stable, iron(iv)-oxo complex, [Fe(2PyN2Q)(O)]2+ was directed for hydrogen atom abstraction (HAA) from aliphatic substrates and the iron(ii)-halide [FeII(2PyN2Q)(X)]+ (X, halogen) was exploited in conjunction to deliver the halogen atom to the ensuing carbon centered radical. Despite iron(iv)-oxo being an effective promoter of hydroxylation of aliphatic substrates, the perfect interplay of HAA and halogen atom transfer in this work leads to the halogenation product selectively by diverting the hydroxylation pathway. Experimental studies outline the mechanistic details of the iron(iv)-oxo mediated halogenation reactions. A kinetic isotope study between PhCH3 and C6D5CD3 showed a value of 13.5 that supports the initial HAA step as the RDS during halogenation. Successful implementation of this new strategy led to the establishment of a functional mimic of non-heme halogenase enzymes with an excellent selectivity for halogenation over hydroxylation. Detailed theoretical studies based on density functional methods reveal how the small difference in the ligand design leads to a large difference in the electronic structure of the [Fe(2PyN2Q)(O)]2+ species. Both experimental and computational studies suggest that the halide rebound process of the cage escaped radical with iron(iii)-halide is energetically favorable compared to iron(iii)-hydroxide and it brings in selective formation of halogenation products over hydroxylation.
- Rana, Sujoy,Biswas, Jyoti Prasad,Sen, Asmita,Clémancey, Martin,Blondin, Geneviève,Latour, Jean-Marc,Rajaraman, Gopalan,Maiti, Debabrata
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p. 7843 - 7858
(2018/10/31)
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- A alkane halogenation method (by machine translation)
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The invention relates to a cycloalkane of halogenation method, comprises the following steps: S1: taking inorganic hydrohalide salt M+ X- And the inorganic acid or organic acid, stirring to dissolve in water, containing the halide X- Aqueous solution; S2: light in the reactor will be put aqueous solution, add nanometer metal/semiconductor composite material photocatalyst, phase transfer catalyst and reaction substrate cycloalkane; S3: under the stirring condition, in the sunlight or 300W xenon lamp or LED light shifted to catalytic reaction; S4: reaction after the fluid is static set, filtering and recycling photocatalyst, separating and recovering the aqueous phase and then, drying the organic phase, and the dried organic phase rectification separation purification, to obtain the corresponding organic halogenated product. The present invention provides a method halide of the cycloalkanes, low cost, the apparatus is simple and easy to operate, high selectivity, easy separation, can be large-scale production, is a novel, environmental protection, high selectivity, low energy consumption of the new organic halide, viable green channels, with potential industrial application value. (by machine translation)
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Paragraph 0046; 0047; 0054; 0055
(2017/07/21)
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- Site-selective aliphatic C-H bromination using N -bromoamides and visible light
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Transformations that selectively functionalize aliphatic C-H bonds hold significant promise to streamline complex molecule synthesis. Despite the potential for site-selective C-H functionalization, few intermolecular processes of preparative value exist. Herein, we report an approach to unactivated, aliphatic C-H bromination using readily available N-bromoamide reagents and visible light. These halogenations proceed in useful chemical yields, with substrate as the limiting reagent. The site selectivities of these radical-mediated C-H functionalizations are comparable (or superior) to the most selective intermolecular C-H functionalizations known. With the broad utility of alkyl bromides as synthetic intermediates, this convenient approach will find general use in chemical synthesis.
- Schmidt, Valerie A.,Quinn, Ryan K.,Brusoe, Andrew T.,Alexanian, Erik J.
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supporting information
p. 14389 - 14392
(2014/12/10)
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- Revisiting the bromination of c-h bonds with molecular bromine by using a photo-microflow system
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The photobromination of C-H bonds by using molecular bromine was reinvestigated under microfluidic conditions. The continuous-flow method suppressed the production of dibrominated compounds and effectively produced the desired monobrominated products with high selectivity. Rapid bromination of benzylic substrates containing a photoaffinity azide group was achieved without any decomposition. Go with the (micro)flow: Photobromination of C-H bonds by using molecular bromine under microfluidic conditions has been investigated (see scheme). The continuous-flow method suppressed the production of dibrominated compounds and effectively produced the desired monobrominated compounds with high selectivity. Rapid bromination of benzylic substrates containing a photoaffinity azide group was achieved without any decomposition.
- Manabe, Yoshiyuki,Kitawaki, Yuriko,Nagasaki, Masahiro,Fukase, Koichi,Matsubara, Hiroshi,Hino, Yoshiko,Fukuyama, Takahide,Ryu, Ilhyong
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supporting information
p. 12750 - 12753
(2015/03/30)
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- A facile and green protocol for nucleophilic substitution reactions of sulfonate esters by recyclable ionic liquids [bmim][X]
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Ionic liquids [bmim][X] (X = Cl, Br, I, OAc, SCN) are highly efficient reagents for nucleophilic substitution reactions of sulfonate esters derived from primary and secondary alcohols. The counter anions (X-) of the ionic liquids, [bmim][X], effectively replace the sufonates affording the corresponding substitution products such as alkyl halides, acetates, and thiocyanides in excellent yields. The newly developed protocol is very environmentally attractive because the reactions use stoichiometric amounts of ionic liquids as sole reagents in most cases and do not require additional solvents, any other activating reagents, non-conventional equipment, or special precautions. Moreover, these ionic liquids can be readily recycled without loss of reactivity, making the whole process greener.
- Liu, Yajun,Xu, Yongnan,Jung, Sun Ho,Chae, Junghyun
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p. 2692 - 2698,7
(2012/12/12)
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- A facile and green protocol for nucleophilic substitution reactions of sulfonate esters by recyclable ionic liquids [bmim][X]
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Ionic liquids [bmim][X] (X = Cl, Br, I, OAc, SCN) are highly efficient reagents for nucleophilic substitution reactions of sulfonate esters derived from primary and secondary alcohols. The counter anions (X-) of the ionic liquids, [bmim][X], effectively replace the sufonates affording the corresponding substitution products such as alkyl halides, acetates, and thiocyanides in excellent yields. The newly developed protocol is very environmentally attractive because the reactions use stoichiometric amounts of ionic liquids as sole reagents in most cases and do not require additional solvents, any other activating reagents, non-conventional equipment, or special precautions. Moreover, these ionic liquids can be readily recycled without loss of reactivity, making the whole process greener. Georg Thieme Verlag KG Stuttgart · New York.
- Liu, Yajun,Xu, Yongnan,Jung, Sun Ho,Chae, Junghyun
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p. 2692 - 2698
(2013/01/15)
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- Stereoretentive halogenations and azidations with titanium(IV) enabled by chelating leaving groups
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Titaniumdoes it again! With the help of nucleophile-assisting leaving groups (NALGs), alkyl bromides, iodides, and, for the first time, azides are obtained from sulfonates withcomplete retention of configuration. Critical to the design of these new titanium(IV) reactions has been the use of NALGs which are thought to chelate the Lewis acid reagent in the transition state promoting an SNi-type mechanism. (Chemical Equation Presented)
- Lepore, Salvatore D.,Mondal, Deboprosad,Song, Ye Li,Bhunia, Anjan K.
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supporting information; body text
p. 7511 - 7514
(2009/03/12)
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- Chemoselective monobromination of alkanes promoted by unactivated MnO 2
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Reaction of alkanes with bromine promoted by unactivated MnO2 gave the corresponding alkylbromides in excellent yield with good chemoselectivity. The MnO2 could be easily recovered and reused.
- Jiang, Xuefeng,Shen, Meihua,Tang, Yu,Li, Chaozhong
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p. 487 - 489
(2007/10/03)
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- Direct bromination and iodination of non-activated alkanes by hypohalite reagents
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The direct functionalisation of alkanes through bromination and iodination has been successfully achieved. The combination of stoichiometric mixtures of elemental halogen and sodium alkoxides leads to the formation of alkyl hypobromites and hypoiodites as reagents. The halogenation occurs without external photostimulation under thermal reaction conditions. Georg Thieme Verlag Stuttgart.
- Montoro, Raul,Wirth, Thomas
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p. 1473 - 1478
(2007/10/03)
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- Carbonylation of C7-C8 cycloalkanes leading to individual tertiary carbonyl-containing compounds
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Carbonylation of cycloheptane, methylcyclohexane, cyclooctane and ethylcyclohexane by CO in the presence of CBr4·2AlBr3 at -40°C and 1 atm was performed with good yields and selectivities. Individual esters of tertiary carboxylic aci
- Akhrem,Afanas'eva,Petrovskii,Vitt,Orlinkov
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p. 9903 - 9907
(2007/10/03)
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- Reactions of nucleophiles with 5-(alkoxy)thianthrenium ions
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Reactions of 5-(alkoxy)thianthrenium perchlorates (1) with weakly basic nucleophiles Br-, I- and PhS- (X-) in MeCN and DMSO led to SN2 substitution, E2C elimination, and reaction at sulfornium sulfur to extents depending on the structure of the alkoxy group (RO) in 1 and the nucleophile. Three types of reaction occurred with R = cyclopentyl (1a), cyclohexyl (1b), cis- (1c) and trans- 4-methylcyclohexyl (1d) and cycloheptyl (1e), and X- = Br and I-. That is, SN2 reaction gave RX and thianithrene 5-oxide (ThO), E2C reaction gave cycloalkene and ThO and reaction at sulfonium sulfur gave X2, thianthrene (Th) and cycloalkanol (ROH). Earlier work with R = Me (1f) and Et (1g) and X- = I-. Br- had shown that only SN2 reaction occurred. In contrast with reactions of halide ions, reactions of PhS- with 1b-g occurred only at sulfonium sulfur, giving Th, ROH and PhSSPh (DPDS). For comparison with 1, reactions of Ph2S+OMe (2) with I- and PhS- were carried out. Reaction with I- gave only Ph2S=O and Mel (SN2), Reaction with PhS- gave very little PhSMe (SN2) but mainly Ph2S, MeOH, and DPDS from reaction at sulfonium sulfur. The differences in nucleophilic pathways (PhS- vs Br- and I-) in reactions with 1 and 2 are attributed to differences in thiophilicities of the nucleophiles. The thiophilicity of PhS- dominates its reactions with 1 and 2. The direction toward products (Th, ROH and DPDS) in these reactions is compounded by the ease of displacement of alkoxide from 1 and 2 by PhS-, and the ease with which, subsequently, thiophilic PhS- attacks sulfenyl sulfur in the resulting phenylthiosulfonium ion. Copyright
- Liu, Bo,Shine, Henry J.,Zhao, Wenyi
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p. 827 - 836
(2007/10/03)
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- Esterification of carboxylic acid salts
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Mono- or polycarboxylic acid esters are prepared by reacting a salt of such carboxylic acid with an organic halocompound, e.g., a (cyclo)alkyl, (cyclo)alkenyl, aryl or aralkyl halide, in an aqueous reaction medium, in the presence of a catalytically effective amount of a phase transfer catalyst, for example an onium salt.
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- Homolytic Ring Fission reactions of Bicycloalkanes and Bicycloalk-2-yl Radicals: Electron Spin Resonance Study of Cycloalkenylmethyl Radicals
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Hydrogen abstraction from bicycloalkanes (n=3-6) by t-butoxyl radicals was examined by an e.s.r. technique.The main site of attack was C(2) giving bicycloalk-2-yl radicals which rearranged by β-scission of the outer cyclopropane bonds to give cycloalkenylmethyl radicals.This is in contrast to the bicycloalk-2-yl radicals (n=1,2) which rearranged by fission of the inter-ring bonds to give cycloalkenyl radicals. β-Scission in bicycloalk-2-yl radicals was examined by semi-empirical SCF MO calculations.The conformations and barriers to internal rotation of the cycloalkenylmethyl radicals were determined from the variation in the β-H hyperfine splitting constants with temperature.Photobromination of bicycloalkanes (n=3,4) was also investigated in CCl4 solution.The main process was bimolecular homolytic substitution (SH2) by bromine atoms at the cyclopropane carbons, but there was an increase in hydrogen abstraction with ring size.The SH2 reactions parallel the β-scission reactions of the bicycloalk-2-yl radicals in that the main bond undergoing fission changes from the inter-ring bond to the outer cyclopropane bond as the ring size increases.
- Roberts, Charles,Walton, John C.
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p. 879 - 886
(2007/10/02)
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- Aliphatic Hydroxylation Catalyzed by Iron Porphyrin Complexes
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The hydroxylation of unactivated alkanes has been observed in a catalytic system containing iodosylbenzene and various iron porphyrins.The yields and distributions of products have been found to be sensitive to the peripheral substitution pattern of the porphyrin.The oxidation of cyclohexane with chloro(5,10,15,20-tetra-o-tolylporphyrinato)iron(III) gave a 31percent yield of cyclohexanol and 6percent cyclohexanone based on iodosylbenzene.Two samples of Fe(TTP)ClCl with differing atropisomeric composition gave different product ratios.The hydroxylation of cycloheptane under these conditions and in the presence of bromotrichloromethane gave 24percent cycloheptanol and 18percent bromocycloheptane.Steric selectivity was observed by comparing the hydroxylation of cis-decalin with Fe(TPP)Cl, Fe(TTP)Cl, Fe(TNP)Cl, and Fe(TMP)Cl.The hydrogen-isotope effect for cyclohexane hydroxylation by Fe(TTP)Cl was found to be 12.9+/- 1.A mechanism for hydroxylation is proposed on the basis of these results that involves initial oxidation of the iron porphyrin, hydrogen atom abstraction from the alkane, and rapid collapse of this radical to give the product alcohol and to regenerate the iron(III) catalyst.
- Groves, John T.,Nemo, Thomas E.
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p. 6243 - 6248
(2007/10/02)
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- OXIDATION OF N-ALKYL-N'-TOSYLHYDRAZINES WITH BROMINE
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Oxidation of N-alkyl-N'-tosylhydrazines with bromine yield alkyl bromides, vicinal alkyl dibromides and traces of alcohols.The main products of primary hydrazines are monobromides whereas secondary hydrazines preferably produce dibromides.The reaction proceeds with evolution of nitrogen and hydrobromic acid and by the formation of intermediate sulfinic ester wich may be isolated.Various substrates were examined under different conditions to confirm the validity of the reaction mechanism hypothesized.
- Palmieri, Gianni
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p. 4097 - 4102
(2007/10/02)
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