- Utilization of o-[(E)-2-trimethylsilyl-2-iodovinyl]phenylthio derivatives as carbon radical precursors by anchimeric approach
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o-[(E)-2-Trimethylsilyl-2-iodovinyl]phenylthio derivatives have been introduced as effective precursors for the generation of carbon centered radicals even in the presence of certain nucleophiles; this provides useful information about the structural requirement for inducing an efficient anchimeric effect under mild conditions.
- Ooi,Furuya,Sakai,Hokke,Maruoka
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- Photocatalytic Reductive C-O Bond Cleavage of Alkyl Aryl Ethers by Using Carbazole Catalysts with Cesium Carbonate
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Methods to activate the relatively stable ether C-O bonds and convert them to other functional groups are desirable. One-electron reduction of ethers is a potentially promising route to cleave the C-O bond. However, owing to the highly negative redox potential of alkyl aryl ethers (Ered -2.6 V vs SCE), this mode of ether C-O bond activation is challenging. Herein, we report the visible-light-induced photocatalytic cleavage of the alkyl aryl ether C-O bond using a carbazole-based organic photocatalyst (PC). Both benzylic and non-benzylic aryl ethers underwent C-O bond cleavage to form the corresponding phenol products. Addition of Cs2CO3 was beneficial, especially in reactions using a N-H carbazole PC. The reaction was proposed to occur via single-electron transfer (SET) from the excited-state carbazole to the substrate ether. Interaction of the N-H carbazole PC with Cs2CO3 via hydrogen bonding exists, which enables a deprotonation-assisted electron-transfer mechanism to operate. In addition, the Lewis acidic Cs cation interacts with the substrate alkyl aryl ether to activate it as an electron acceptor. The high reducing ability of the carbazole combined with the beneficial effects of Cs2CO3 made this otherwise formidable SET event possible.
- Yabuta, Tatsushi,Hayashi, Masahiko,Matsubara, Ryosuke
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p. 2545 - 2555
(2021/02/01)
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- A facile and versatile electro-reductive system for hydrodefunctionalization under ambient conditions
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A general electrochemical system for reductive hydrodefunctionalization is described, employing the inexpensive and easily available triethylamine (Et3N) as a sacrificial reductant. This protocol is characterized by facile operation, sustainable conditions, and exceptionally wide substrate scope covering the cleavage of C-halogen, N-S, N-C, O-S, O-C, C-C and C-N bonds. Notably, the selectivity and capability of reduction can be conveniently switched by simple incorporation or removal of an alcohol as a co-solvent.
- Huang, Binbin,Guo, Lin,Xia, Wujiong
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supporting information
p. 2095 - 2103
(2021/03/26)
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- Transfer Hydrogenation of Alkenes Using Ethanol Catalyzed by a NCP Pincer Iridium Complex: Scope and Mechanism
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The first general catalytic approach to effecting transfer hydrogenation (TH) of unactivated alkenes using ethanol as the hydrogen source is described. A new NCP-type pincer iridium complex (BQ-NCOP)IrHCl containing a rigid benzoquinoline backbone has been developed for efficient, mild TH of unactivated C-C multiple bonds with ethanol, forming ethyl acetate as the sole byproduct. A wide variety of alkenes, including multisubstituted alkyl alkenes, aryl alkenes, and heteroatom-substituted alkenes, as well as O- or N-containing heteroarenes and internal alkynes, are suitable substrates. Importantly, the (BQ-NCOP)Ir/EtOH system exhibits high chemoselectivity for alkene hydrogenation in the presence of reactive functional groups, such as ketones and carboxylic acids. Furthermore, the reaction with C2D5OD provides a convenient route to deuterium-labeled compounds. Detailed kinetic and mechanistic studies have revealed that monosubstituted alkenes (e.g., 1-octene, styrene) and multisubstituted alkenes (e.g., cyclooctene (COE)) exhibit fundamental mechanistic difference. The OH group of ethanol displays a normal kinetic isotope effect (KIE) in the reaction of styrene, but a substantial inverse KIE in the case of COE. The catalysis of styrene or 1-octene with relatively strong binding affinity to the Ir(I) center has (BQ-NCOP)IrI(alkene) adduct as an off-cycle catalyst resting state, and the rate law shows a positive order in EtOH, inverse first-order in styrene, and first-order in the catalyst. In contrast, the catalysis of COE has an off-cycle catalyst resting state of (BQ-NCOP)IrIII(H)[O(Et)···HO(Et)···HOEt] that features a six-membered iridacycle consisting of two hydrogen-bonds between one EtO ligand and two EtOH molecules, one of which is coordinated to the Ir(III) center. The rate law shows a negative order in EtOH, zeroth-order in COE, and first-order in the catalyst. The observed inverse KIE corresponds to an inverse equilibrium isotope effect for the pre-equilibrium formation of (BQ-NCOP)IrIII(H)(OEt) from the catalyst resting state via ethanol dissociation. Regardless of the substrate, ethanol dehydrogenation is the slow segment of the catalytic cycle, while alkene hydrogenation occurs readily following the rate-determining step, that is, β-hydride elimination of (BQ-NCOP)Ir(H)(OEt) to form (BQ-NCOP)Ir(H)2 and acetaldehyde. The latter is effectively converted to innocent ethyl acetate under the catalytic conditions, thus avoiding the catalyst poisoning via iridium-mediated decarbonylation of acetaldehyde.
- Wang, Yulei,Huang, Zhidao,Leng, Xuebing,Zhu, Huping,Liu, Guixia,Huang, Zheng
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supporting information
p. 4417 - 4429
(2018/04/05)
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- Synthesis of Benzyl Alkyl Ethers by Intermolecular Dehydration of Benzyl Alcohol with Aliphatic Alcohols under the Effect of Copper Containing Catalysts
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Synthesis of benzyl alkyl ethers was performed in high yields by intermolecular dehydration of benzyl and primary, secondary, tertiary alcohols under the effect of copper containing catalysts. The formation of benzyl alkyl ethers occurs with participation of benzyl cation.
- Bayguzina,Gimaletdinova,Khusnutdinov
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p. 1148 - 1155
(2018/10/24)
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- Tetrahydroxydiboron-Mediated Palladium-Catalyzed Transfer Hydrogenation and Deuteriation of Alkenes and Alkynes Using Water as the Stoichiometric H or D Atom Donor
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There are few examples of catalytic transfer hydrogenations of simple alkenes and alkynes that use water as a stoichiometric H or D atom donor. We have found that diboron reagents efficiently mediate the transfer of H or D atoms from water directly onto unsaturated C-C bonds using a palladium catalyst. This reaction is conducted on a broad variety of alkenes and alkynes at ambient temperature, and boric acid is the sole byproduct. Mechanistic experiments suggest that this reaction is made possible by a hydrogen atom transfer from water that generates a Pd-hydride intermediate. Importantly, complete deuterium incorporation from stoichiometric D2O has also been achieved.
- Cummings, Steven P.,Le, Thanh-Ngoc,Fernandez, Gilberto E.,Quiambao, Lorenzo G.,Stokes, Benjamin J.
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supporting information
p. 6107 - 6110
(2016/06/09)
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- Organic chemistry: A general alkyl-alkyl cross-coupling enabled by redox-active esters and alkylzinc reagents
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Alkyl carboxylic acids are ubiquitous in all facets of chemical science, from natural products to polymers, and represent an ideal starting material with which to forge new connections. This study demonstrates how the same activating principles used for decades to make simple C-N (amide) bonds from carboxylic acids with loss of water can be used to make C-C bonds through coupling with dialkylzinc reagents and loss of carbon dioxide. This disconnection strategy benefits from the use of a simple, inexpensive nickel catalyst and exhibits a remarkably broad scope across a range of substrates (>70 examples).
- Qin, Tian,Cornella, Josep,Li, Chao,Malins, Lara R.,Edwards, Jacob T.,Kawamura, Shuhei,Maxwell, Brad D.,Eastgate, Martin D.,Baran, Phil S.
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p. 801 - 805
(2016/06/01)
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- Vanadium-Catalyzed Oxidative Debenzylation of O-Benzyl Ethers at ppm Level
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An advantageous methodology for the oxidative debenzylation of ethers has been developed. Very low amounts of a catalyst system based on vanadyl acetylacetonate and a triazole type pincer ligand allow the selective oxidative cleavage of a number of O-benzyl ethers in the presence of oxygen as the sole oxidant. The methodology tolerates a number of functional groups such as halo-, alkoxy-, or trifluoromethylarenes, alkyne, alkene, ether, and acetal units. Large-scale deprotections can be also carried out by the optimized procedure, which is amenable to enantioenriched reactants as well. (Figure presented.).
- Urgoitia, Garazi,SanMartin, Raul,Herrero, María Teresa,Domínguez, Esther
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supporting information
p. 3307 - 3312
(2016/10/21)
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- Visible-light-promoted conversion of alkyl benzyl ether to alkyl ester or alcohol via O-α-sp3 C-H cleavage
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A mild and high-yielding visible-light-promoted conversion of alkyl benzyl ethers to the alkyl esters or alkyl alcohols was developed. Mechanistic studies provided evidence for a radical chain reaction involving the homolytic cleavage of O-α-sp3 C-H bonds in the substrate as one of the propagation steps. We propose that α-bromoethers are key intermediates in the transformation.
- Lu, Ping,Hou, Tianyuan,Gu, Xiangyong,Li, Pixu
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supporting information
p. 1954 - 1957
(2015/04/27)
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- Light-mediated deoxygenation of alcohols with a dimeric gold catalyst
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A new protocol for the reductive deoxygenation of primary alcohols was explored. This photo-mediated method combines a novel approach to bromination of alcohols merged with the powerful reducing capability of [Au2(dppm)2]Cl2 [dppm = 1,1-bis(diphenylphosphino)methane] as a photoredox catalyst. The highly efficient methods discussed are marked by the use of UVA light-emitting diodes, which have significantly reduced reaction times and lowered setup cost.
- McCallum, Terry,Slavko, Ekaterina,Morin, Mathieu,Barriault, Louis
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supporting information
p. 81 - 85
(2015/02/18)
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- Selective catalytic synthesis of unsymmetrical ethers from the dehydrative etherification of two different alcohols
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The cationic ruthenium-hydride complex [(C6H6)(PCy3)(CO)RuH]+BF4- catalyzes selective etherification of two different alcohols to form unsymmetrically substituted ethers. The catalytic method exhibits a broad substrate scope while tolerating a range of heteroatom functional groups in forming unsymmetrical ethers, and it is successfully used to directly synthesize a number of highly functionalized chiral nonracemic ethers.
- Kim, Junghwa,Lee, Dong-Hwan,Kalutharage, Nishantha,Yi, Chae S.
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p. 3881 - 3885
(2015/01/16)
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- Tandem ring-closing metathesis/transfer hydrogenation: Practical chemoselective hydrogenation of alkenes
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An operationally simple chemoselective transfer hydrogenation of alkenes using ruthenium metathesis catalysts is presented. Of great practicality, the transfer hydrogenation reagents can be added directly to a metathesis reaction and effect hydrogenation of the product alkene in a single pot at ambient temperature without the need to seal the vessel to prevent hydrogen gas escape. The reduction is applicable to a range of alkenes and can be performed in the presence of aryl halides and benzyl groups, a notable weakness of Pd-catalyzed hydrogenations. Scope and mechanistic considerations are presented.
- Connolly, Timothy,Wang, Zhongyu,Walker, Michael A.,McDonald, Ivar M.,Peese, Kevin M.
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supporting information
p. 4444 - 4447
(2015/01/09)
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- CATALYTIC C-H BOND ACTIVATION FOR THE SYNTHESIS OF ETHERS AND THIOETHERS
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Disclosed is a method for the transition metal-mediated oxidation of C-H bonds to form C-0 or C-S bonds. The methods are useful for the formation of ethers (R-OR') from alcohols, R'OH, and sp3 -hybridized C-H bonds in substrates, R-H. Aryl or heteroaryl acetates may also be used for C-H to C-OAr bond formation. The methods are also useful in the preparation of C-S bonds from acetyl-protected thiols, MeC(0)SR, and disulfides, RSSR. Advantageously, the methods minimize reaction steps, the handling of oxidized intermediates, and environmental impact.
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Page/Page column 5; 42
(2014/01/08)
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- Hydrogen-free alkene reduction in continuous flow
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The first continuous hydrogenation that requires neither H2 nor metal catalysis generates diimide by a novel reagent combination. The simple flow reactor employed minimizes residence time by enabling safe operation at elevated temperature.
- Kleinke, Andrew S.,Jamison, Timothy F.
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supporting information
p. 710 - 713
(2013/03/29)
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- A novel method for synthesis of benzyl alkyl ethers using Vanadium-based metal complex catalysts
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A novel method has been developed for the synthesis of benzyl alkyl ethers in 25-85% yields via the reaction of toluene with alcohols in a CCl4 medium catalyzed by Et3N-activated VO(acac)2.
- Khusnutdinov,Bayguzina,Gallyamova,Dzhemilev
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p. 261 - 266
(2012/10/29)
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- Engaging unactivated alkyl, alkenyl and aryl iodides in visible-light-mediated free radical reactions
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Radical reactions are a powerful class of chemical transformations. However, the formation of radical species to initiate these reactions has often required the use of stoichiometric amounts of toxic reagents, such as tributyltin hydride. Recently, the use of visible-light-mediated photoredox catalysis to generate radical species has become popular, but the scope of these radical precursors has been limited. Here, we describe the identification of reaction conditions under which photocatalysts such as fac-Ir(ppy) 3 can be utilized to form radicals from unactivated alkyl, alkenyl and aryl iodides. The generated radicals undergo reduction via hydrogen atom abstraction or reductive cyclization. The reaction protocol utilizes only inexpensive reagents, occurs under mild reaction conditions, and shows exceptional functional group tolerance. Reaction efficiency is maintained upon scale-up and decreased catalyst loading, and the reaction time can be significantly shortened when the reaction is performed in a flow reactor.
- Nguyen, John D.,D'Amato, Erica M.,Narayanam, Jagan M. R.,Stephenson, Corey R. J.
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p. 854 - 859
(2012/11/07)
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- Highly efficient two-step synthesis of C-sp3-centered geminal diiodides
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(Chemical Equation Presented) Trisubstituted gem-diiodoalkenes of functionalized chains are efficiently reduced to the corresponding terminal geminal diiodides in high yields upon treatment with the diazene precursor, diethyl 4-(hydrazinosulfonyl)-benzyl phosphonate.
- Cloarec, Jean-Manuel,Charette, Andre B.
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p. 4731 - 4734
(2007/10/03)
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- Ether synthesis using trifluoromethanesulfonic anhydride or triflates under mild reaction conditions
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Reactions of magnesium alkoxides with trifluoromethanesulfonic anhydride or triflates gave corresponding symmetrical or unsymmetrical ethers in moderate to good yields under mild reaction conditions. The scope and limitations of the reaction are discussed.
- Nishiyama, Tomihiro,Kameyama, Hideaki,Maekawa, Hideki,Watanuki, Kouhei
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p. 258 - 262
(2007/10/03)
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- Novel reactions of ethylene acetals with silyl-substituted nucleophiles. A mild and efficient procedure for the synthesis of homoallyl alkyl ethers and unsymmetrical dialkyl ethers
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Efficient one-pot synthesis of homoallyl alkyl ethers and dialkyl ethers was performed by the allylation and reduction of ethylene acetals with allyltrimethylsilane and t-butyldimethylsilane, respectively, in the presence of alkoxytrimethylsilane.
- Suzuki, Takeshi,Oriyama, Takeshi
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p. 1263 - 1269
(2007/10/03)
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- Unique property of copper(I) chloride as a radical initiator as well as a Lewis acid: Application to CuCl-catalyzed aldol reaction of α,β- unsaturated ketones with Bu3SnH
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Copper (I) chloride in combination with tributyltin hydride showed unique character as an initiator of certain radical reactions. Hydrostannation of α,β-unsaturated ketones with Bu3SnH was initiated by CuCl and the resulting tin enolates underwent subsequent aldol reaction with aldehydes under the influence of CuCl as a Lewis acid catalyst.
- Ooi, Takashi,Doda, Kanae,Sakai, Daiki,Maruoka, Keiji
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p. 2133 - 2136
(2007/10/03)
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- Mechanistic studies of the free-radical fragmentation of monoalkyl diazenes
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Mechanistic studies of the deoxygenation of primary alcohols by Mitsumobu displacement with o-nitrobenzenesulfonylhydrazine (NBSH) reveal that the monoalkyl diazene intermediates formed in this process are exceedingly good hydrogen-atom donors toward alkyl radicals, exceeding tri-n-butylin hydride in reactivity. Competition experiments are described wherein the radical intermediates are trapped by intra- and intermediate addition to carbon-carbon double bonds, to dioxygen, and to the free radical 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO).
- Myers, Andrew G.,Movassaghi, Mohammad,Zheng, Bin
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p. 6569 - 6572
(2007/10/03)
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- Synthesis of benzyl/allyl alkyl ethers from corresponding magnesium alkoxides
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In the presence of iodine, alcohols react with magnesium to produce magnesium alkoxides which are then treated with benzyl chloride or allyl bromide to produce benzyl alkyl ethers or allyl alkyl ethers.
- Lin, Ji-Mao,Li, Hui-Hui,Zhou, Ai-Min
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p. 5159 - 5160
(2007/10/03)
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- Rearrangement of Aromatic Acetals Over Solid Acid Catalysts
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The reactions of aromatic acetals (1a-6a) catalysed by aluminium phosphate (AP) yield the corresponding esters (b), ethers (c) and the parent aldehydes (d).Similar reactions over aluminium sulphate (AS) give only esters (b) and the aldehydes (d).Probable mechanisms have been suggested for the reactions.The catalysts have been characterized by various studies.The specific poisoning of the catalysts have been done with NH3 and CO2 and the product formation on the poisoned catalyst provides support to the suggested mechanisms.
- Xavier, N.,Arulraj, S. J.
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p. 519 - 522
(2007/10/02)
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- REGIOSELECTIVE BOND CLEAVAGE AND COORDINATION EFFECTS IN THE REDUCTION OF SOME ACETALS WITH LITHIUM IN AMMONIA
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Some benzylic-type acetals possessing the 2,8-dioxabicyclo(3.2.1)octane ring system are cleaved in a regioselective manner when treated with lithium in ammonia.The results from various reductions implicate coordination of lithium as a significant factor involved in reduction mechanisms.
- Abell, A. D.,Massy-Westropp, R. A.
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p. 2451 - 2464
(2007/10/02)
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- ACTIVATION BY PdCl2(PhCN)2 OF THE ALCOHOLIC BENZYLIC FUNCTION TO NUCLEOPHILIC ALIPHATIC AS WELL AS ELECTROPHILIC AROMATIC SUBSTITUTIONS. A ONE STEP SYNTHESIS OF A CHROMANE STRUCTURE
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Benzylic alcohols react, by activation with PdCl2(PhCN)2, under mild conditions with alkanols and enols to give the corresponding benzylic ethers, and, under the same conditions, with aromatic substrates to give the corresponding phenylmethanes.As an example, a one-step synthesis of a chromane structure is reported.
- Mincione, Enrico,Bovicelli, Paolo
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p. 437 - 440
(2007/10/02)
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- Mercury-assisted solvolyses of alkyl halides. Simple procedures for the preparation of nitrate esters, acetate esters, alcohols and ethers
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The reactions of a wide variety of alkyl halides with mercury(I) and/or (II) nitrate in 1,2-dimethoxyethane, mercury(II) acetate in acetic acid, aqueous mercury(II) perchlorate, and mercury(II) perchlorate in alcohol solvents have been investigated; as a result, simple high yield procedures for the conversion of alkyl halides into the corresponding nitrate esters, acetate esters, alcohols and ethers have been developed.
- McKillop,Ford
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p. 2467 - 2475
(2007/10/05)
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