- Visual sensing of Ca2+ ion via photoreaction of fluorenyl ester-armed cyclen
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Fluorenyl ester-armed cyclen gave fluorenone and related decomposition compounds upon photoirradiation. The reaction was effectively suppressed by the formation of an octacoordinated Ca2+ complex while Na+ and other alkali/alkaline earth metal cations had little influence. Since the production efficiency of fluorescent fluorenone related well to the concentration of the Ca2+ ion, the photoreaction of this armed cyclen offered the naked-eye detection of Ca2+ ion in aqueous samples. The Royal Society of Chemistry 2005.
- Player, Tomoko N.,Shinoda, Satoshi,Tsukube, Hiroshi
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- Non-heme iron(III) complex with tridentate ligand: Synthesis, structures and catalytic oxidations of alkanes
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We report synthesis and characterization of a mononuclear iron(III) complex [Fe(LH2)Cl2]+, 1 having tridentate ligand LH2 and their application in oxidation of alkanes. Complex, 1 was characterized by various analytical, spectroscopic, electrochemical, crystallographic and theoretical studies. The molecular structure determination showed the presence of distorted square pyramidal FeN3Cl2 coordination sphere. Selective oxidation of benzyl alcohol, fluorene, adamantane, 1-phenyl ethanol and n-octane in presence of catalytic amount [FeIII(LH2)Cl2]+ with H2O2 under mild conditions give products in good to excellent yields through FeIV[dbnd]O intermediate. Several studies were done to support the reactive intermediate. Generation of FeIV[dbnd]O intermediate was also supported by UV–visible titration of [FeIII(LH2)Cl2]+ and H2O2 at low temperature and their visual colour change from red (500 nm, ? = 1050 M? 1 cm? 1) to green (770 nm, ? = 153 M? 1 cm? 1).
- Tyagi, Nidhi,Singh, Ovender,Ghosh, Kaushik
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- REACTIONS OF METHYLYTTERBIUM IODIDE WITH ACTIVE HYDROGEN COMPOUNDS
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Methylytterbium iodide (CH3YbI) has been found to react with active hydrogen compounds such as phenylacetylene and fluorene to give phenylpropynoic acid and fluorenol in modest yields.The reactivity of CH3YbI to these active hydrogen compounds is far higher than of CH3MgI.
- Yokoo, Kazuhiri,Kijima, Yasushi,Fujiwara, Yuzo,Taniguchi, Hiroshi
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- One-pot diastereoselective synthesis of new racemic and achiral spirohydantoins
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An efficient and versatile method was used for the diastereoselective synthesis of achiral and racemic spirohydantoins based on ketones 4, 5, 7 and 10.
- Mahmoodi, Nosrat O.,Khodaee, Ziba
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- Structural basis for the properties of two single-site proline mutants of CYP102A1 (P450BM3)
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The crystal structures of the haem domains of Ala330Pro and Ile401Pro, two single-site proline variants of CYP102A1 (P450BM3) from Bacillus megaterium, have been solved. In the A330P structure, the active site is constricted by the relocation of the Pro329 side chain into the substrate access channel, providing a basis for the distinctive C-H bond oxidation profiles given by the variant and the enhanced activity with small molecules. I401P, which is exceptionally active towards non-natural substrates, displays a number of structural similarities to substrate-bound forms of the wild-type enzyme, notably an off-axial water ligand, a drop in the proximal loop, and the positioning of two I-helix residues, Gly265 and His266, the reorientation of which prevents the formation of several intrahelical hydrogen bonds. Second-generation I401P variants gave high in vitro oxidation rates with non-natural substrates as varied as fluorene and propane, towards which the wild-type enzyme is essentially inactive. The substrate-free I401P haem domain had a reduction potential slightly more oxidising than the palmitate-bound wild-type haem domain, and a first electron transfer rate that was about 10 % faster. The electronic properties of A330P were, by contrast, similar to those of the substrate-free wild-type enzyme. Protein evolution with proline: The crystal structures of two contrasting single-site proline mutants of CYP102A1 (P450BM3) have been solved. The two mutations combine to give a variant that shows substantially enhanced catalytic activity with small non-natural substrates (see graph).
- Whitehouse, Christopher J. C.,Yang, Wen,Yorke, Jake A.,Rowlatt, Benjamin C.,Strong, Anthony J. F.,Blanford, Christopher F.,Bell, Stephen G.,Bartlam, Mark,Wong, Luet-Lok,Rao, Zihe
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- Pd-Catalyzed Assembly of Fluoren-9-ones by Merging of C-H Activation and Difluorocarbene Transfer
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We disclose a novel Pd-catalyzed assembly of fluoren-9-ones by merging of C-H activation and difluorocarbene transfer. ClCF2COONa served as a difluorocarbene precursor to be harnessed as a carbonyl source in this transformation. The current protocol enables us to afford fluoren-9-ones in high yields with excellent functional group compatibility, which also represents the first example of using difluorocarbene as a coupling partner in transition-metal-catalyzed C-H activation.
- Liu, Xiaobing,Sheng, Heyun,Zhou, Yao,Song, Qiuling
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- Nucleofugal behavior of a β-shielded α-cyanovinyl carbanion
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Sterically well-shielded against unsolicited Michael addition and polymerization reactions, α-metalated α-(1,1,3,3-tetramethyl-indan-2-ylidene)acetonitriles added reversibly to three small aldehydes and two bulky ketones at room temperature. Experimental conditions were determined for transfer of the nucleofugal title carbanion unit between different carbonyl compounds. These readily occurring retro-additions via C-C(O) bond fission may also be used to generate different metal derivatives of the nucleofugal anions as equilibrium components. Fluoride-catalyzed, metal-free desilylation admitted carbonyl addition but blocked the retro-addition.
- Knorr, Rudolf,Schmidt, Barbara
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- ENHANCEMENT OF Si-H BOND REACTIVITY IN PENTACOORDINATED STRUCTURES
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The reactions of pentacoordinated silicon dihydrides with alcohols, carboxylic acids and carbonyl compounds have been studied.The dihydrides are markedly more reactive than the corresponding tetracoordinated species.
- Boyer, J.,Breliere, C.,Corriu, R. J. P.,Kpoton, A.,Poirier, M.,Royo, G.
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- Isolation, structure and iridium-mediated decarbonylation of a sodium fluorenone dianion complex
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Reaction of fluorenone with 2 equiv. of Na in THF at room temp, gave the polymeric Na-fluorenone dianion complex 1 in 79% isolated yield, which upon reaction with 0.5 equiv. of [(C5Me5)IrCl(μ-Cl)]2 afforded the decarbonylation product 2; both 1 and 2 have been structurally characterized.
- Hou, Zhaomin,Fujita, Akira,Yamazaki, Hiroshi,Wakatsuki, Yasuo
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- Selective aerobic benzylic C-H oxidation co-catalyzed by N-hydroxyphthalimide and Keplerate {Mo72V30} nanocluster
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The catalytic efficiency of a Keplerate {Mo72V30} nanocapsule in the aerobic benzylic C-H oxidation of alcohols and hydrocarbons was exploited. The aerobic reactions were conducted using catalytic amounts of {Mo72V30} and under the co-catalytic effects of NHPI (N-hydroxyphthalimide) to furnish desired aldehydes and ketones in high yields and excellent selectivity. Different benzylic alcohols and hydrocarbons were shown to be amenable to oxidation under standard conditions presented here. Spectral data and leaching experiments revealed that the cluster had a long-term stability and could be used repeatedly in consecutive runs.
- Rezaeifard, Abdolreza,Khoshyan, Ashkan,Jafarpour, Maasoumeh,Pourtahmasb, Mehrdad
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- INTERMEDIATES IN THE DECOMPOSITION OF ALIPHATIC DIAZO-COMPOUNDS. PART 19. KINETICS AND MECHANISM OF THE REACTIONS OF 9-DIAZOFLUORENE CATION RADICAL
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The decomposition of 9-diazofluorene (FlN2) brought about at a platinum anode or by chemical oxidants, Cu(BF4)2 or (p-BrC6H4)3N(+.)SbCl6(1-), in CH3CN solution leads to formation of mixtures of bifluorenylidene and flourenone azine in high yield.The reactions have been studied kinetically by conventional means and using the transient electrochemical techniques derivative linear sweep voltammetry (l.s.v.) and derivative cyclic voltammetry (d.c.v.).Constant-current electrolysis of FlN2 shows the characteristics of a chain process.The chemical oxidants give rise to a rate law -d/dt = k above a critical oxidant level, and the value of k is the same for both oxidants, even though their oxidation potentials are substantially different.It is inferred that the process studied is the chain propagation step in which the chain carrier reacts with a molecule of FlN2.Under the conditions of l.s.v. and d.c.v. experiments, it is shown that the instantaneously formed FlN2(+.) is consumed in a rapid process which is second order with respect to the cation radical and has a rate constant of 1.9 x 1E8 l mol-1 s-1; it is suggested that this process is cation radical dimerisation.Since the product of this step rapidly yields bifluorenylidene, it is argued that the slower macroscopic chain reactions do not involve dimerisation, but rather that FlN2(+.) rapidly attacks a further FlN2 molecule to generate the chain carrier which must have a lower oxidation potential than FlN2(+.).Possible structures for the chain carrier are considered in the light of earlier e.s.r. evidence for a radical intermediate.
- Ahmad, Iftikhar,Bethell, Donald,Parker, Vernon D.
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- The fluorenyl cation
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The fluorenyl cation is a textbook example for a 4πantiaromatic cation. However, contrasting results have been published on how the annelated benzene rings compensate the destabilizing effect of the 4π antiaromatic five-membered ring in its core. Whereas previous attempts to synthesize this cation in superacidic media resulted in undefined polymeric material only, we herein report that it can be generated and isolated in amorphous water ice at temperatures below 30 K by photolysis of diazofluorene. Under these conditions, the fluorenylidene is protonated by water to give the fluorenyl cation, which could be characterized spectroscopically. Its absorption in the visible-light range matches that previously obtained by ultrafast absorption spectroscopy, and furthermore, its IR spectrum could be recorded. The IR bands in amorphous ice very nicely match predictions from DFT and DFT/MM calculations, suggesting the absence of strong interactions between the cation and surrounding water molecules.
- Costa, Paolo,Trosien, Iris,Fernandez-Oliva, Miguel,Sanchez-Garcia, Elsa,Sander, Wolfram
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- Sodium Aminodiboranate, a New Reagent for Chemoselective Reduction of Aldehydes and Ketones to Alcohols
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Sodium aminodiboranate (NaNH 2(BH 3) 2, NaADBH) is a new member of the old borane family, which exhibits superior performance in chemoselective reduction. Experimental results show that NaADBH can rapidly reduce aldehydes and ketones to the corresponding alcohols in high efficiency and selectivity under mild conditions. There are little steric and electronic effects on this reduction.
- Wang, Jin,Guo, Yu,Li, Shouhu,Chen, Xuenian
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supporting information
p. 1104 - 1108
(2021/05/25)
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- A General Method for Photocatalytic Decarboxylative Hydroxylation of Carboxylic Acids
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A general and practical method for decarboxylative hydroxylation of carboxylic acids was developed through visible light-induced photocatalysis using molecular oxygen as the green oxidant. The addition of NaBH4 to in situ reduce the unstable peroxyl radical intermediate much broadened the substrate scope. Different sp3 carbon-bearing carboxylic acids were successfully employed as substrates, including phenylacetic acid-type substrates, as well as aliphatic carboxylic acids. This transformation worked smoothly on primary, secondary, and tertiary carboxylic acids.
- Khan, Shah Nawaz,Zaman, Muhammad Kashif,Li, Ruining,Sun, Zhankui
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p. 5019 - 5026
(2020/05/01)
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- Reagents and methods for esterification
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A method for esterification of one or more carboxylic acid groups in a compound containing one or more carboxylic acid groups wherein the esterification reagent is a diazo-compound of formula: wherein the R1 and R2 groups of the diazo compound are selected such that the corresponding organic compound of formula: exhibits a —C—H pKa value between 18 and 29 as measured in DMSO. Specific reagents and methods for esterification are provided. The esterification reagents provided exhibit high selectivity for esterification of carboxylic acid groups over reaction with amine, alcohol or thiol groups in the compound containing one or more carboxylic acid groups. The method can be used to selectively esterify carboxylic acid groups in peptides or proteins.
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Page/Page column 22-24
(2020/03/18)
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- 1-D manganese(ii)-terpyridine coordination polymers as precatalysts for hydrofunctionalisation of carbonyl compounds
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Reductive catalysis with earth-abundant metals is currently of increasing importance and shows potential in replacing precious metal catalysis. In this work, we revealed catalytic hydroboration and hydrosilylation of ketones and aldehydes achieved by a structurally defined manganese(ii) coordination polymer (CP) as a precatalyst under mild conditions. The manganese-catalysed methodology can be applied to a range of functionalized aldehydes and ketones with turnover numbers (TON) of up to 990. Preliminary results on the regioselective catalytic hydrofunctionalization of styrenes by the Mn-CP catalyst are also presented.
- Johnson, Jahvon,Li, Sihan,Mo, Zixuan,Neary, Michelle C.,Zeng, Haisu,Zhang, Guoqi,Zheng, Shengping
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supporting information
p. 2610 - 2615
(2020/03/05)
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- Erratum: Redox-Noninnocent Ligand-Supported Vanadium Catalysts for the Chemoselective Reduction of C=X (X = O, N) Functionalities (Journal of the American Chemical Society (2019) 141:38 (15230-15239) DOI: 10.1021/jacs.9b07062)
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Pages 15232, 15233, and 15236. In the original paper, the doublet wave functions for 21 and 21a/21b were incorrectly (Figure Presented). reported as spin-contaminated in sections 2.3 and 2.8 (Figure 3 and Scheme 9, respectively.) This comes from the incorrectly reported expected eigenvalue of 0.75 for the spin-squared operator ??2? for the antiferromagnetically coupled doublet |↓?L|↑↑?V state (originally given in the Supporting Information). The correct expected eigenvalue for the |↓?L|↑↑?V state should be 1.75. The wave functions for 21 and 21a/21b (eigenvalues 1.79 and 1.77/1.66, respectively) are therefore not spincontaminated. The corrected Figure 3 and Scheme 9 are presented below. A corrected Supporting Information file is also provided. The corrections do not affect any of the conclusions of the Article, but slightly decrease the gap between the quartet and doublet spin surfaces. Scheme 3 has been also corrected to reflect the fact that (CH3)3SiCH2 ? radicals can only react based on spin conservation.
- Zhang, Guoqi,Wu, Jing,Zheng, Shengping,Neary, Michelle C.,Mao, Jincheng,Flores, Marco,Trovitch, Ryan J.,Dub, Pavel A.
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supporting information
p. 16507 - 16509
(2020/10/14)
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- Selective oxidation of benzyl alcohol to benzaldehyde, 1-phenylethanol to acetophenone and fluorene to fluorenol catalysed by iron (II) complexes supported by pincer-type ligands: Studies on rapid degradation of organic dyes
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Hexacoordinated non-heme iron complexes [FeII(L1)2](ClO4)2 (1) and [FeII(L2)2](PF6)2 (2) have been synthesized using ligands L1?=?(E)-2-chloro-6-(2-(pyridin-2ylmethylene) hydrazinyl)pyridine and L2?=?(E)-2-chloro-6-(2-(1-(pyridin-2-yl)ethylidene)hydrazinyl) pyridine]. These complexes are highly active non-heme iron catalysts to catalyze the C (sp3)?H bonds of alkanes. These iron complexes have been characterized using ESI?MS analysis and molecular structures were determined by X-ray crystallography. ESI???MS analysis also helped to understand the generation of intermediate species like FeIII?OOH and FeIV=O. DFT and TD?DFT calculations revealed that the oxidation reactions were performed through high-valent iron center and a probable reaction mechanism was proposed. These complexes were also utilized for the degradation of orange II and methylene blue dyes.
- Singh, Ovender,Gupta, Priyanka,Singh, Anshu,Maji, Ankur,Singh, Udai P.,Ghosh, Kaushik
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- N-Doped carbon nanofibers derived from bacterial cellulose as an excellent metal-free catalyst for selective oxidation of arylalkanes
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N-Doped carbon nanofibers derived from one-step pyrolysis of low-cost bacterial cellulose with the assistance of urea were reported. Owing to their interconnected nanofibrous structure and high specific surface area as well as high N doping, they exhibited excellent catalytic performance for selective oxidation of arylalkanes even with O2 as an oxidant in aqueous solution.
- Huang, Runkun,Cao, Changyan,Liu, Jian,Sun, Dongping,Song, Weiguo
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supporting information
p. 1935 - 1938
(2019/05/02)
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- Panel of New Thermostable CYP116B Self-Sufficient Cytochrome P450 Monooxygenases that Catalyze C?H Activation with a Diverse Substrate Scope
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The ability of cytochrome P450 monooxygenases to catalyse a wide variety of synthetically challenging C?H activation reactions makes them highly desirable biocatalysts both for the synthesis of chiral intermediates and for late-stage functionalisations. However, P450s are plagued by issues associated with poor expression, solubility and stability. Catalytically self-sufficient P450s, in which the haem and reductase domains are fused in a single protein, obviate the need for additional redox partners and are attractive as biocatalysts. Here we present a panel of natural self-sufficient P450s from thermophilic organisms (CYP116B65 from A. thermoflava, CYP116B64 from A. xiamenense, CYP116B63 from J. thermophila, CYP116B29 from T. bispora and CYP116B46 from T. thermophilus). These P450s display enhanced expression and stability over their mesophilic homologues. Activity profiling of these enzymes revealed that each P450 displayed a different fingerprint in terms of substrate range and reactivity that cover reactions as diverse as hydroxylation, demethylation, epoxidation and sulfoxidation. The productivity of the bio-transformation of diclofenac to produce the 5-hydroxy metabolite increased 42-fold using the thermostable P450-AX (>0.5 g L?1 h?1) compared to the P450-RhF system reported previously. In conclusion, we have generated a toolkit of thermostable self-sufficient P450 biocatalysts with a broad substrate range and reactivity.
- Tavanti, Michele,Porter, Joanne L.,Sabatini, Selina,Turner, Nicholas J.,Flitsch, Sabine L.
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p. 1042 - 1051
(2018/03/21)
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- Liquid-phase oxidation of alkylaromatics to aromatic ketones with molecular oxygen over a Mn-based metal-organic framework
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Liquid-phase oxidation of alkylaromatics with molecular O2 was examined using a microporous Mn-based metal-organic framework (Mn-MOF-74). Mn-MOF-74 consisting of trimeric Mn clusters and 2,5-dihydroxyterephthalate (dhtp) linkers exhibits superior catalytic activity with good ketone selectivity compared to conventional oxide-supported Mn catalysts without showing any lengthy induction period. Combined analyses by means of XRD, FE-SEM, N2 physisorption and Mn K-edge XAFS reveal that the superior catalytic performance is attributed to the inherently-formed Mn(iii)2(dhtp) moieties embedded in the Mn-MOF-74 framework rather than structural factors associated with the MOF. The catalyst is reusable over multiple catalytic runs along with retaining its original catalytic activity due to the ability of the dhtp ligand to stabilize active Mn(iii) atoms. Owing to high activity, reusability and nontoxicity, Mn-MOF-74 can offer a simple, inexpensive and efficient protocol for the oxidation of some important alkylaromatics, such as ethylbenzene and diphenylmethane to produce the corresponding aromatic ketones.
- Kuwahara, Yasutaka,Yoshimura, Yukihiro,Yamashita, Hiromi
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supporting information
p. 8415 - 8421
(2017/07/12)
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- Photocatalytic Decarboxylative Hydroxylation of Carboxylic Acids Driven by Visible Light and Using Molecular Oxygen
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This paper discloses the first example of photocatalytic direct decarboxylative hydroxylation of carboxylic acids. It enables the conversion of a variety of readily available carboxylic acids to alcohols in moderate to high yields. This unprecedented protocol is accomplished under extremely mild reaction conditions using molecular oxygen (O2) as a green oxidant and using visible light as a driving force.
- Song, Hai-Tao,Ding, Wei,Zhou, Quan-Quan,Liu, Jing,Lu, Liang-Qiu,Xiao, Wen-Jing
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p. 7250 - 7255
(2016/08/30)
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- Exploring the Reactivity of α-Lithiated Aryl Benzyl Ethers: Inhibition of the [1,2]-Wittig Rearrangement and the Mechanistic Proposal Revisited
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By carefully controlling the reaction temperature, treatment of aryl benzyl ethers with tBuLi selectively leads to α-lithiation, generating stable organolithiums that can be directly trapped with a variety of selected electrophiles, before they can undergo the expected [1,2]-Wittig rearrangement. This rearrangement has been deeply studied, both experimentally and computationally, with aryl α-lithiated benzyl ethers bearing different substituents at the aryl ring. The obtained results support the competence of a concerted anionic intramolecular addition/elimination sequence and a radical dissociation/recombination sequence for explaining the tendency of migration for aryl groups. The more favored rearrangements are found for substrates with electron-poor aryl groups that favor the anionic pathway.
- Velasco, Rocío,Silva López, Carlos,Nieto Faza, Olalla,Sanz, Roberto
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p. 15058 - 15068
(2016/10/11)
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- Sulfonic acid-functionalized LUS-1: an efficient catalyst for tetrahydropyranylation/depyranylation of alcohols
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Efficient acidic functionalization of mesoporous silica LUS-1 (Laval University Silica) and its application as a recyclable heterogeneous catalyst for DHP (3,4-dihydro-2H-pyran) protection of alcohols and the subsequent removal of the corresponding protecting group have been reported. This green method offers a number of advantages such as short reaction time, good yields of protection and deprotection, simple work-up procedure, recyclable catalyst, and environmentally friendly conditions.
- Rahimifard, Mahshid,Mohammadi Ziarani, Ghodsi,Badiei, Alireza
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p. 6327 - 6336
(2016/07/06)
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- Diazo compounds for the bioreversible esterification of proteins
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A diazo compound is shown to convert carboxylic acids to esters efficiently in an aqueous environment. The basicity of the diazo compound is critical: low basicity does not lead to a reaction but high basicity leads to hydrolysis. This reactivity extends to carboxylic acid groups in a protein. The ensuing esters are hydrolyzed by human cellular esterases to regenerate protein carboxyl groups. This new mode of chemical modification could enable the key advantages of prodrugs to be translated from small-molecules to proteins. This journal is
- McGrath, Nicholas A.,Andersen, Kristen A.,Davis, Amy K. F.,Lomax, Jo E.,Raines, Ronald T.
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p. 752 - 755
(2015/02/18)
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- Fabrication of CuCr2O4 spinel nanoparticles: A potential catalyst for the selective oxidation of cycloalkanes via activation of Csp3-H bond
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We report here preparation of CuCr2O4 spinel nanoparticle catalyst, mediated by cationic surfactant CTAB in hydrothermal route. XRD revealed the formation of CuCr2O4 spinel phase and TEM showed the particle size of 30-60 nm. The catalyst was speculated to be highly active for selective oxidation of cyclohexane to cyclohexanone with H2O2. A cyclohexane conversion of 70% with 85% cyclohexanone selectivity was achieved over this catalyst at 50 °C temperature. Moreover, the catalyst did not show any significant activity loss even after 8 reuses and proved its efficacy in the oxidation of other cycloalkanes also.
- Acharyya, Shankha S.,Ghosh, Shilpi,Adak, Shubhadeep,Tripathi, Deependra,Bal, Rajaram
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p. 145 - 150
(2015/01/09)
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- Mesoporous Silica-Supported Amidozirconium-Catalyzed Carbonyl Hydroboration
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The hydroboration of aldehydes and ketones using a silica-supported zirconium catalyst is reported. Reaction of Zr(NMe2)4 and mesoporous silica nanoparticles (MSN) provides the catalytic material Zr(NMe2)n@MSN. Exhaustive characterization of Zr(NMe2)n@MSN with solid-state (SS)NMR and infrared spectroscopy, as well as through reactivity studies, suggests its surface structure is primarily ≡ SiOZr(NMe2)3. The presence of these nitrogen-containing zirconium sites is supported by 15N NMR spectroscopy, including natural abundance 15N NMR measurements using dynamic nuclear polarization (DNP) SSNMR. The Zr(NMe2)n@MSN material reacts with pinacolborane (HBpin) to provide Me2NBpin and the material ZrH/Bpin@MSN that is composed of interacting surface-bonded zirconium hydride and surface-bonded borane ≡ SiOBpin moieties in an approximately 1:1 ratio, as well as zirconium sites coordinated by dimethylamine. The ZrH/Bpin@MSN is characterized by 1H/2H and 11B SSNMR and infrared spectroscopy and through its reactivity with D2. The zirconium hydride material or the zirconium amide precursor Zr(NMe2)n@MSN catalyzes the selective hydroboration of aldehydes and ketones with HBpin in the presence of functional groups that are often reduced under hydroboration conditions or are sensitive to metal hydrides, including olefins, alkynes, nitro groups, halides, and ethers. Remarkably, this catalytic material may be recycled without loss of activity at least eight times, and air-exposed materials are catalytically active. Thus, these supported zirconium centers are robust catalytic sites for carbonyl reduction and that surface-supported, catalytically reactive zirconium hydride may be generated from zirconium-amide or zirconium alkoxide sites.
- Eedugurala, Naresh,Wang, Zhuoran,Chaudhary, Umesh,Nelson, Nicholas,Kandel, Kapil,Kobayashi, Takeshi,Slowing, Igor I.,Pruski, Marek,Sadow, Aaron D.
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p. 7399 - 7414
(2015/12/11)
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- Copper-catalyzed benzylic oxidation of C(sp3)-H bonds
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A selective oxidation of benzylic C(sp3)-H bonds to C(sp 3)-O bonds catalyzed by copper complexes of quinoline-imine ligands was developed with peresters as oxidants under mild reaction conditions, which converted benzylic methylenes directly into benzylic alcohols and esters by means of direct C-H bond functionalization.
- Zhang, Bo,Zhu, Shou-Fei,Zhou, Qi-Lin
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supporting information
p. 2033 - 2037
(2013/03/13)
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- Magnesium-catalysed hydroboration of aldehydes and ketones
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The heteroleptic magnesium alkyl complex [CH{C(Me)NAr}2Mg nBu] (Ar = 2,6-iPr2C6H3) is reported as a highly efficient pre-catalyst for the hydroboration of aldehydes and ketones with pinacolborane. The Royal Society of Chemistry 2012.
- Arrowsmith, Merle,Hadlington, Terrance J.,Hill, Michael S.,Kociok-Koehn, Gabriele
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supporting information; experimental part
p. 4567 - 4569
(2012/06/05)
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- Acid-, water- and high-temperature-stable ruthenium complexes for the total catalytic deoxygenation of glycerol to propane
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The ruthenium aqua complexes [Ru(H2O)2(bipy) 2](OTf)2, [cisRu(6,6′-Cl2-bipy) 2(OH2O)2)] (OTf)2, [Ru(H 2O)2(phen)2](OTf)2, [Ru(H 2O)3(2,2′:6′,2″-terpy)](OTf) 2 and [Ru(H2O)3(Phterpy)] (OTf)2 (bipy = 2,2′-bipyridine; OTf- = triflate; phen = phenanthroline; terpy = terpyridine; Phterpy = 4′-phenyl-2,2′: 6′,2″-terpyridine) are water- and acid-stable catalysts for the hydrogenation of aldehydes and ketones in sulfolane solution. In the presence of HOS(O)2CF3 (triflic acid) as a dehydration co-catalyst they directly convert 1,2-hexanediol to n-hexanol and hexane. The terpyridine complexes are stable and active as catalysts at temperatures ≥ 250°C and in either aqueous sulfolane solution or pure water convert glycerol into n-propanol and ultimately propane as the final reaction product in up to quantitative yield. For the terpy complexes the active catalyst is postulated to be a carbonyl species [(4′-R-2,2′:6′,2″-terpy)Ru(CO) (H2O)2]-(OTf)2 (R = H, Ph) formed by the decarbonylation of aldehydes (hexanal for 1,2-hexanediol and 3-hydroxypropanal for glycerol) generated in the reaction mixture through acid-catalyzed dehydration. The structure of the dimeric complex [{(4′-phenyl-2,2′: 6′,2″-terpy)Ru(CO)}2(μ-OCH3) 2](OTf)2 has been determined by single crystal X-ray crystallography (Space group P1 (a = 8.2532(17); b = 12.858(3); C = 14.363(3) A; α = 64.38(3); β = 77.26(3); γ = 87.12(3)°, R = 4.36%).
- Taher, Deeb,Thibault, Michelle E.,Di Mondo, Domenico,Jennings, Michael,Schlaf, Marcel
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supporting information; experimental part
p. 10132 - 10143
(2010/04/03)
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- Ruthenium(II) complex catalysts bearing a pyridyl-supported pyrazolyl-imine ligand for transfer hydrogenation of ketones
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A new class of hemilabile unsymmetrical 2-(1-arylimino)-6-(pyzazol-1-yl)pyridine ligands and their ruthenium(II) and nickel(II) NNN complexes were synthesized. The Ru(II) complex catalysts have been fully characterized and exhibited good to excellent catalytic activity in the transfer hydrogenation (TH) of ketones in refluxing 2-propanol. These results have demonstrated rare examples of active ruthenium(II) NNN complex catalysts that do not feature a N-H functionality for TH of ketones.
- Zhao, Miao,Yu, Zhengkun,Yan, Shenggang,Li, Yang
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experimental part
p. 3068 - 3075
(2009/12/08)
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- Metal-Free: An efficient and selective catalytic aerobic oxidation of hydrocarbons with oxime and N-Hydroxyphthalimide
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A non-metal catalytic system consisting of dimethylglyoxime (DMG) and N-hydroxyphthal-imide (NHPI) for the selective oxidation of hydrocarbons with dioxygen is described. The synergistic effect of DMG and NHPI ensures its efficient catalytic ability: 82.1% conversion of ethylbenzene with 94.9% selectivity for acetophenone could be obtained at 80°C under 0.3 MPa of dioxygen in 10h. Several hydrocarbons were efficiently oxidized to their corresponding oxygenated products under mild conditions. aerobic oxidation; catalyst design; dimethylglyoxime ; hydrocarbons ; N-hydroxyphthalimide
- Zheng, Gengxiu,Liu, Chunhong,Wang, Qiufen,Wang, Mingyu,Yang, Guanyu
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scheme or table
p. 2638 - 2642
(2009/12/30)
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- A free radical process for oxidation of hydrocarbons promoted by nonmetal xanthone and tetramethylammonium chloride under mild conditions
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A nonmetal catalytic system consisting of N-hydroxyphthalimide, xanthone, and tetramethylammonium chloride was developed. A wide range of hydrocarbons could be oxidized efficiently with dioxygen under mild conditions. In the presence of xanthone and tetramethylammonium chloride, catalytic activity of N-hydroxyphthalimide was greatly improved, and selectivity for alkyl hydroperoxide was remarkably decreased.
- Du, Zhongtian,Sun, Zhiqiang,Zhang, Wei,Miao, Hong,Ma, Hong,Xu, Jie
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supporting information; experimental part
p. 1677 - 1680
(2009/09/05)
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- Alteration of the substrate specificity of the angular dioxygenase carbazole 1,9a-dioxygenase
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Carbazole 1,9a-dioxygenase (CARDO) consists of terminal oxygenase (CARDO-O) and electron transport components. CARDO can catalyze specific oxygenation for various substrates: angular dioxygenation for carbazole and dibenzo-p-dioxin, lateral dioxygenation for anthracene, and monooxygenation for methylene carbon of fluorene and sulfide sulfur of dibenzothiophene. To elucidate the molecular mechanism determining its unique substrate specificity, 17 CARDO-O site-directed mutants at amino acid residues I262, F275, Q282, and F329, which form the substrate-interacting wall around the iron active site by CARDO-O crystal structure, were generated and characterized. F329 replacement dramatically reduced oxygenation activity. However, several mutants produced different products from the wild-type enzyme to a large extent: I262V and Q282Y (1-hydroxycarbazole), F275W (4-hydroxyfluorene), F275A (unidentified cis-dihydrodiol of fluoranthene), and I262A and I262W (monohydroxydibenzothiophenes). These results suggest the possibility that the respective substrates bind to the active sites of CARDO-O mutants in a different orientation from that of the wild-type enzyme.
- Uchimura, Hiromasa,Horisaki, Tadafumi,Umeda, Takashi,Noguchi, Haruko,Usami, Yusuke,Li, Li,Terada, Tohru,Nakamura, Shugo,Shimizu, Kentaro,Takemura, Tetsuo,Habe, Hiroshi,Furihata, Kazuo,Omori, Toshio,Yamane, Hisakazu,Nojiri, Hideaki
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body text
p. 3237 - 3248
(2009/04/10)
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- WO3/70% TBHP/aqueous NaOH: An efficient catalytic combination for the selective oxidation of methylarenes and alkyl aryl ketones to benzoic acids
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A new solvent-free, reusable catalytic combination consisting of WO 3/70% TBHP/aqueous NaOH has been described for the direct oxidation of methylarenes and acetophenones to the corresponding benzoic acids in high yields. Alkylarenes are oxidized to the corresponding aromatic ketones or benzylic alcohols depending upon whether NaOH is used or not. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.
- Shaikh, Tanveer Mahammad Ali,Sudalai, Arumugam
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experimental part
p. 4877 - 4880
(2009/05/30)
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- Vanadium(I) chloride and lithium vanadium(I) dihydride as selective epimetallating reagents for π- and σ-bonded organic substrates
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Subvalent vanadium(I) salts, of empirical formulas, VCl, vanadium(I) chloride and LiVH2, lithium vanadium(I) dihydride, whose efficient preparation, structural constitution and mode of reaction toward certain organic substrates have been described in a preceding article, are here evaluated in their reactions toward a wide variety of π- and σ-bonded organic substrates, namely carbonyl, imine, azo, alkene, 1,3-diene, nitrile π-bonds and C-X, C-O, C-N and N-N σ-bonds. Compared with the high reactivity of CrCl and LiCrH2 reagents in attacking both types of bonds, the VCl and LiVH2 reagents were much milder and selective in epimetallating π-bonds, often forming the 1:1 adduct of LiVH2 and π-bonded substrate as the major product. Finally, the vanadium reagents showed little tendency to cleave C-O, C-S and C-N bonds and a smaller scope in cleaving C-X bonds than their chromium counterparts. Because of their selectivity these vanadium reagents offer the following preparative promise: 1) smooth McMurry carbonyl coupling to their reductive dimers; 2) deoxygenation of epoxides; 3) selective aromatic C-X reduction; 4) high yields of epimetallated carbonyls or imines as intermediates to α-hydroxy and α-amino acids; 5) 1,4-reductions of 1,3-alkadienes; 6) reductive dimerization of nitriles to ketones; 7) 1,4 or 1,n-epimetallations leading to acyloins or indoles; and 8) reductive dimerizations of azines to produce unusual imidazole derivatives. In explaining the greater kinetic stability of the 1:1 LiVH2 adduct with carbonyl or imine substrates it is pointed out that such epimetallated adducts from LiVH2 would likely be diamagnetic, whereas such adducts from LiCrH2 have an unpaired electron on the Cr center and hence would rupture, so that the electron would be on the C center. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.
- Eisch, John J.,Fregene, Paul O.
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scheme or table
p. 4482 - 4492
(2009/05/07)
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- Vanadium(I) chloride and lithium vanadium(I) dihydride as epimetallating reagents for unsaturated organic substrates: Constitution and mode of reaction
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Subvalent vanadium(I) salts, of empirical formulas, VCl, vanadium(I) chloride and LiVH2, lithium vanadium(I) dihydride, can be conveniently prepared in THF solution, starting at -78 °C, by treating either VCl3 or VCl4 with an appropriate number of equivalents of nBuLi. As judged by the stability of solutions or solid samples of LiVH2, the preparation of LiVH2 from VCl4 is the preferred method. Individual physical characterization of solid samples of VCl or of LiVH2, admixed with their LiCl by-product, was carried out after removal of all volatiles in vacuo and by the following measurements: 1) gasometric protolysis with glacial acetic acid and measurement of the H 2 evolved in the oxidation of VI to VII; 2) infrared spectroscopic search for V-H bands; and 3) examination for unpaired electrons by EPR activity. Such measurements applied to VCl lend strong support for a VI oxidation state but only probable evidence for paramagnetism and for the association of VCl units. Similar measurements applied to LiVH 2 give unambiguous gasometric and IR evidence favoring the LiVH 2 stoichiometry and the biradical nature of the VH2 anion with a linear array of H-V-H atoms. Chemical characterization of both VCl and LiVH2 toward individual organic substrates, such as olefins, ketones, epoxides and organic halides, yielded convincing evidence that organic radical mechanisms are involved, both for the proven biradical, LiVH2, as well as for the diamagnetic VCl. Finally, the question of why LiVH2 prepared from VCl4 is more stable than the LiVH2 obtained from VCl3 is addressed in terms of the actual coordination sphere of the VH2 anion in THF solution and in the solid state. Preliminary studies comparing the reactivities of LiVH2 and LiCrH2 toward organic substrates indicate that LiVH2 is the distinctly more moderate and usefully selective reductant. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.
- Eisch, John J.,Fregene, Paul O.,Doetschman, David C.
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experimental part
p. 2825 - 2835
(2009/04/07)
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- The epimetallation and carbonation of carbonyl and imino derivatives: Epivanadation route to 2-amino and 2-hydroxy acids
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The feasibility of hydrocarboxylating carbonyl and imino derivatives by the two-step process of epimetallation and carbonation has been demonstrated with the model substrates of 9-fluorenone and 9-fluorenone anil. With lithium vanadium dihydride as the epimetallating agent, such hydrocarboxylation has led to a 75% yield of 9-hydroxy-9-fluorenecarboxylic acid and a 65% yield of 9-(N-phenylamino)-9-fluorenecarboxylic acid, respectively. Some initial success in extending the scope of this reaction to other substrates, such as benzophenone, has been achieved by using other epimetallating agents, like the presumed LiV(CH3)2 and Ti(OPri)2. A brief review of the processes and organic synthetic applications of epimetallation and transfer epimetallation of C-C π-bonds is offered as background.
- Eisch, John J.,Fregene, Paul O.,Gitua, John N.
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p. 4647 - 4653
(2008/03/12)
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- Two pseudo-N3 ligands and the catalytic activity of their ruthenium(II) complexes in transfer hydrogenation and hydrogenation of ketones
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Complex RuCl2(PPh3)(iBu-BTP) (5) was synthesized by the reaction of 2,6-bis(5,6-bis(iso-butyl)-1,2,4-triazin-3-yl)pyridine (iBu-BTP) and RuCl2(PPh3)3 in refluxing toluene, and its molecular structure was confirmed by X-ray crystallographic determination. Complex 5 was applied as a catalyst for transfer hydrogenation of ketones and exhibited catalytic activity comparable to RuCl2(PPh3)(Me4BPPy) (1) (Me4BPPy = bis(3,5-dimethylpyrazol-1-yl)pyridine) in some cases. The difference between the catalytic activity of 5 and 1 is attributed to the significantly different arrangement and positions of the PPh3 and chlorides and also to the different electron density on the N-heterocycles. Complex 1 exhibited good to excellent catalytic activity in hydrogenation of ketones under mild conditions. These results have suggested new applications of iBu-BTP and Me4BPPy as promising planar tridentate pseudo-N3 ligands to construct highly active transition-metal catalysts.
- Yu,Zeng,Sun,Deng,Dong,Chen,Wang,Pei
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p. 2306 - 2313
(2008/01/27)
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- Samarium/N-bromosuccinimide-induced reductive dimerization of carbonyl compounds
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Stereoselective reductive coupling of carbonyl compounds has been achieved using samarium/N-bromosuccinimide in methanol. The combination of these agents has proved a powerful addition to the arsenal of samarium-based reductants currently utilized.
- Banik, Bimal K.,Banik, Indrani,Samajdar, Susanta,Cuellar, Rogelio
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p. 2319 - 2322
(2007/10/03)
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- Flow-vacuum pyrolysis of polycyclic compounds. 221 : Pyrolysis of 2,2'-bis(hydroxymethyl)biphenyl
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The flow-vacuum pyrolysis of the title diol, between 600°C - 800°C and 1mm Hg in argon atmosphere, was investigated using GC/MS. The main reaction products were: fluorene, 9-methylfluorene, 9-methylenefluorene; 9,10-dihydrophenanthrene; phenanthrene; 9-hydroxy-9,10-dihydroanthracene; 9-fluorenol; 9-fluorenone; 2-methyl-2'-formylbiphenyl (major product; 38% at 850°C); 2-hydroxymethyl-2'-formylbiphenyl and 2,2'-diphendialdehyde. The amount of products resulted from intramolecular cyclization was 52% at 850°C and the ratio between products with five-member and six-member central ring was 39:13 at 850°C. A radical mechanism explaining the formation of the reaction products is suggested and a comparison between pyrolysis of the title diol and of the previously studied 2,2'-bis(bromomethyl)biphenyl is made.
- Istrati, Daniela,Marton, George,Drǎghici, Constantin,Grigore, Adriana,Banciu, Mircea D.
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p. 719 - 724
(2007/10/03)
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- Photooxidation of aryl alkanes by a decatungstate/triethylsilane system in the presence of molecular oxygen
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Decatungstate photocatalyzes the oxidation of aryl alkanes to the corresponding tertiary hydroperoxides and alcohols, in the presence of molecular oxygen. The addition of triethylsilane to the reaction mixture substantially increases the proportion of hydroperoxide formed.
- Lykakis, Ioannis N.,Orfanopoulos, Michael
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p. 7645 - 7649
(2007/10/03)
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- Pinacol Formation and Reduction of Aromatic Carbonyls with Magnesium-Methanol at Ambient Temperature
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A simple and inexpensive procedure for the pinacol formation of aromatic aldehydes and reduction of aromatic ketones to the corresponding alcohols with magnesium in dry methanol at ambient temperature is reported. The pinacol formation and reduction are proposed to be proceeding by SET from magnesium.
- Khurana, Jitender M.,Bansal, Geeti,Kukreja, Gagan,Pandey, Ravi R.
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p. 1365 - 1371
(2007/10/03)
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- Catalytic olefination of carbonyl compounds. Effect of the structure of the carbonyl compound on the reaction
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The mechanism of the novel reaction of catalytic olefination of carbonyl compounds was studied. The reaction involves the transformation of hydrazones of aromatic aldehydes and ketones into the corresponding dichloroalkenes and symmetrical azines by the treatment with carbon tetrachloride in the presence of CuCl as a catalyst. The stability of intermediate diazoalkanes is the main factor determining the direction of the reaction. In the case of sufficiently stable diazoalkanes, other products can be formed under the reaction conditions along with the products of catalytic olefination.
- Korotchenko,Shastin,Nenaidenko,Balenkova
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p. 492 - 497
(2007/10/03)
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- Facile reductive coupling of benzylic halides with ferrous oxalate dihydrate
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Facile reductive coupling of benzylic halides is reported with ferrous oxalate dihydrate in DMF or HMPA under nitrogen atmosphere at 155-160°C. The coupling is proposed to proceed by two successive oxidative additions of benzylic halides to ferrous oxalate to give an intermediate organoiron complex which undergoes concerted dimerization to give the corresponding reductively coupled dimers in high yields.
- Khurana, Jitender M.,Chauhan, Sushma,Maikap, Golak C.
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p. 1737 - 1740
(2007/10/03)
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- The decomposition of diazo-compounds induced by nucleophiles. The decomposition of 9-diazofluorene in the presence of hydroxide or alkoxide ions
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9-Diazofluorene, on treatment with stoichiometric or substoichiometric amounts of quaternary ammonium hydroxide or methoxide or of potassium t-butoxide in solution in aqueous or alcoholic dimethyl sulfoxide or acetonitrile at 30°C, decomposes with evolution of nitrogen to yield fluorenone azine [bis(fluorenylidene)hydrazine] in almost quantitative yield. Studies are reported of the identity of the minor by-products, together with an examination of the kinetics of the reactions and additional spectroscopic experiments. The general rate equation is v = k[FIN2]3/2[Nu-]1/2, where Nu- represents the nucleophile. It is concluded that the oxyanions, most probably after nucleophilic attack on 9-diazofluorene under these basic conditions to generate a new anionic species, are capable of transferring an electron to the diazo-compound. This initiates decomposition of further diazo-molecules in a process of electron-transfer chain catalysis that bears some similarities to, but has also some differences from, that encountered using cathodic initiation. In support of this interpretation it is found that reactions can be accelerated by the introduction of carbon acids (fluorene, 9-phenylfluorene) into the reaction mixtures. The nature of the initiation, propagation and termination steps of the chain mechanism are discussed.
- McDowell, Linda J.,Khodaei, M. Mehdi,Bethell, Donald
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p. 995 - 1003
(2007/10/03)
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- Cerium(III) bromate as a new reagent in oxidation of organic compounds
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Cerium(III) bromate, prepared by the reaction of barium bromate with cerium(III) sulfate, can be used for the oxidation of alkylarenes, alcohols, and sulfides. Products are obtained in high yields under mild conditions. Ce(BrO3)3 is an unique, dual property reagent in which the anion is the oxidant and the cation a catalyst. Stoichiometric studies indicate that bromate is reduced to bromide under these conditions, making the process highly efficient.
- Shaabani, Ahmad,Lee, Donald G.
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p. 1845 - 1854
(2007/10/03)
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- Facile reduction of aromatic aldehydes, ketones, diketones and oxo aldehydes to alcohols by an aqueous TiCl3/NH3 system: Selectivity and scope
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A simple and rapid procedure for the almost quantitative reduction of aromatic aldehydes, ketones, diketones and oxo aldehydes to alcohols by use of TiCl3/NH3 in aqueous methanol solution is reported. The reducing system distinguishes between different classes of aldehydes and/or ketones, and many functionalities that usually do not survive under reducing conditions are tolerated well. The concept of reversal of chemoselectivity has also been developed. A mechanism based on two sequential one-electron transfers from TiIII to the carbonyl carbon atom is proposed, the second SET becoming operative only in the presence of ammonium ion (either added or formed in situ). Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002.
- Clerici, Angelo,Pastori, Nadia,Porta, Ombretta
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p. 3326 - 3335
(2007/10/03)
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- Rapid reduction of carbonyls with nickel boride at ambient utemperature
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Carbonyl compounds have been reported to undergo rapid reduction with nickel boride generated in situ from anhyd. nickel chloride and sodium borohydride in THF at ambient temperature to the corresponding alcohols in high yields.
- Khurana,Chauhan
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p. 3485 - 3489
(2007/10/03)
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- Oxygenation reactions of various tricyclic fused aromatic compounds using Escherichia coli and Streptomyces lividans transformants carrying several arene dioxygenase genes.
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Bioconversion (biotransformation) experiments on arenes (aromatic compounds), including various tricyclic fused aromatic compounds such as fluorene, dibenzofuran, dibenzothiophene, carbazole, acridene, and phenanthridine, were done using the cells of Escherichia coli transformants expressing several arene dioxygenase genes. E. coli carrying the phenanthrene dioxygenase (phdABCD) genes derived from the marine bacterium Nocardioides sp. strain KP7 converted all of these tricyclic aromatic compounds, while E. coli carrying the Pseudomonas putida F1 toluene dioxygenase (todC1C2BA) genes or the P. pseudoalcaligenes KF707 biphenyl dioxygenase (bphA1A2A3A4) genes was not able to convert these substrates. Surprisingly, E. coli carrying hybrid dioxygenase (todC1::bphA2A3A4) genes with a subunit substitution between the toluene and biphenyl dioxygenases was able to convert fluorene, dibenzofuran, and dibenzothiophene. The cells of a Streptomyces lividans transformant carrying the phenanthrene dioxygenase genes were also evaluated for bioconversion of various tricyclic fused aromatic compounds. The ability of this actinomycete in their conversion was similar to that of E. coli carrying the corresponding genes. Products converted from the aromatic compounds with these recombinant bacterial cells were purified by column chromatography on silica gel, and identified by their MS and 1H and 13C NMR analyses. Several products, e.g., 4-hydroxyfluorene converted from fluorene, and cis-1,2-dihydroxy-1,2-dihydrophenanthridine, cis-9,10-dihydroxy-9,10-dihydrophenanthridine, and 10-hydroxyphenanthridine, which were converted from phenanthridine, were novel compounds.
- Shindo,Ohnishi,Chun,Takahashi,Hayashi,Saito,Iguchi,Furukawa,Harayama,Horinouchi,Misawa
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p. 2472 - 2481
(2007/10/03)
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- Samarium-induced alkyl halide mediated reductive coupling of ketones
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Reductive coupling of aromatic ketones was achieved by samarium metal in the presence of alkyl halides. (C) 2000 Published by Elsevier Science Ltd.
- Ghatak, Anjan,Becker, Frederick F.,Banik, Bimal K.
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p. 3793 - 3796
(2007/10/03)
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- Alkali and alkaline-earth metal ketyl complexes: Isolation, structural diversity, and hydrogenation/protonation reactions
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The use of hexamethylphosphoric triamide (HMPA) as a stabilizing ligand allowed successful isolation of a series of structurally characterizable alkali metal and calcium ketyl complexes. Reaction of lithium and sodium with one equivalent of fluorenone and reaction of sodium with one equivalent of benzophenone in THF, followed by addition of two equivalents of HMPA, yielded the corresponding ketyl complexes 1, 2, and 11, respectively, as μ-ketyl-bridged dimers. If one equivalent of HMPA was used in the reaction of sodium with fluorenone, a further aggregated complex, the μ3-ketyl-bridged tetramer 3, was isolated, whereas analogous reaction of benzophenone with sodium afforded the trimeric ketyl complex 13, rather than a simple benzophenone analogue of 3. In the reaction of potassium with fluorenone, the use of two equivalents of HMPA gave the tetramer 4, rather than a dimeric complex analogous to 1 or 2. Compared to the tetrameric sodium complex 3, there is an extra HMPA ligand that bridges two of the four K atoms in 4. When 0.5 equiv of HMPA was used in the above reaction, complex 5, a THF-bridged analogue of 4, was isolated. In the absence of HMPA, the reaction of sodium with an excess of fluorenone yielded the tetrameric ketyl complex 6, in which two of the four Na atoms are each terminally coordinated by a fluorenone ligand, and the other two Na atoms are coordinated by a THF ligand. Two bridging THF ligands are also observed in 6. Reaction of 1,2-bis(biphenyl-2,2′-diyl)ethane-1,2-diol (7) with two equivalents of LiN(SiMe3)2 or NaN(SiMe3)2 in the presence of four equivalents of HMPA easily afforded 1 or 2, respectively, via C-C bond cleavage of a 1,2-diolate intermediate. The reaction of calcium with two equivalents of fluorenone or benzophenone in the presence of HMPA gave the corresponding complexes that bear two independent ketyl ligands per metal ion. In the presence of 3 or four equivalents of HMPA, the fluorenone ketyl complex was isolated in a six-coordinate octahedral form (10), while the benzophenone ketyl complex was obtained as a five-coordinate trigonal bipyramid (13). The radical carbon atoms in both benzophenone ketyl and fluorenone ketyl complexes are still in an sp2-hybrid state. However, in contrast with the planar configuration of the whole fluorenone ketyl unit, the radical carbon atom in a benzophenone ketyl species is not coplanar with any of the phenyl groups; this explains why benzophenone ketyl is more reactive than fluorenone ketyl. Hydrolysis of 2 or 11 with 2 N HCl yielded the corresponding pinacol-coupling product, while treatment of 2 or 11 with 2-propanol, followed by hydrolysis, gave the pairs fluorenone and fluorenol or benzophenone and benzhydrol, respectively. A possible mechanism for these reactions is proposed.
- Hou, Zhaomin,Jia, Xueshun,Fujita, Akira,Tezuka, Hiroaki,Yamazaki, Hiroshi,Wakatsuki, Yasuo
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p. 2994 - 3005
(2007/10/03)
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- A variation of titanium-induced carbonyl coupling - Synthesis and conformations of terfluorenyl
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Reaction of fluorenone (4) with a low-valent titanium reagent generated from TiCl4 and Zn in THF in the presence of pyridine gave terfluorenyl (6) in 71% yield, bifluorenylidene (2), the conventional McMurry reaction product, in 2% yield, and additional reduction products. The reductive 'trimerization' was rationalized in terms of an attack of the intermediate fluorenone dianion on bifluorenylidene. The molecular structure of a single crystal of 6 indicated an approximately C2 conformation, with a slightly twisted central ring, and two equally folded side moieties with dihedral angles of 58.1°and 58.0°between the central and side five-membered rings. The AM1 and PM3 calculations showed C2 global minima, similar to the conformation in the crystal. The calculated C(s) transition state conformations were found to be 21.3 (AM1) and 19.9 (PM3) kcal/mol higher in energy than the global C2 minima. A 2D-NMR NOESY experiment on 6 supported the C2 (+sc,+sc) or C2 (-sc,-sc) conformation in solution.
- Pogodin, Sergey,Cohen, Shmuel,Agranat, Israel
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p. 1979 - 1984
(2007/10/03)
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