- Dramatic tuning of ligand donor properties in (Ttz)CuCO through remote binding of H+ (Ttz = hydrotris(triazolyl)borate)
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Complexes with bulky hydrotris(triazolyl)borate (Ttz) ligands, TtzCuCO, were used to probe how acids change the donor properties of Ttz ligands. (TtztBu,Me)CuCO shows four distinct protonation states and a gradual increase in the CO stretch. The increased electrophilic nature of the Cu center upon protonation leads to enhanced C-H activation catalysis.
- Dixon, Natalie A.,McQuarters, Ashley B.,Kraus, Jodi S.,Soffer, Jonathan B.,Lehnert, Nicolai,Schweitzer-Stenner, Reinhard,Papish, Elizabeth T.
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Read Online
- Highly regioselective functionalization of aliphatic carbon-hydrogen bonds with a perbromohomoscorpionate copper(I) catalyst
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The complex TpBr3Cu(NCMe) (1) is an excellent catalyst for the regioselective carbene transfer reaction to tertiary C-H bonds of hydrocarbons, at room temperature, using the readily available ethyl diazoacetate (EDA) as the carbene source. Copyright
- Caballero, Ana,Diaz-Requejo, M. Mar,Belderrain, Tomas R.,Nicasio, M. Carmen,Trofimenko, Swiatoslaw,Perez, Pedro J.
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Read Online
- Alkoxydiaminophosphine Ligands as Surrogates of NHCs in Copper Catalysis
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A family of phosphine ligands containing a five-membered ring similar to the popular N-heterocyclic carbene ligands and an alkoxy third substituent has been developed. These alkoxydiaminophosphine ligands (ADAP) can be generated in one pot and reacted with a copper(I) source leading to the high yield isolation of complexes [(ADAP)CuX]2 (X=Cl, Br). The dinuclear nature of these compounds has been established by means of X-ray studies and DOSY experiments. A screening of the catalytic properties of these complexes toward carbene-transfer reactions from diazocompounds to C?H bonds (alkane, arene), olefins or N?H bonds, as well as in CuAAC or nitrene transfer reactions have shown a performance at least similar, if not better, than their (NHC)CuCl analogues, opening a new window in copper catalysis with these readily tunable ADAP ligands.
- Pizarro, Juan Diego,Molina, Francisco,Fructos, Manuel R.,Pérez, Pedro J.
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supporting information
p. 10330 - 10335
(2020/07/24)
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- Iron-Catalyzed Intermolecular Functionalization of Non-Activated Aliphatic C?H Bonds via Carbene Transfer
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The modification of strong Csp3?H bonds via iron carbene intermediates under mild reaction conditions has been an important challenge with attractive prospective in organic synthesis. In this work, we show the efficient combination of an electrophilic iron catalyst with a lithium Lewis acid for the functionalization of strong Csp3?H bonds of cyclic and linear alkanes by the activation of commercially available ethyl diazoacetate (EDA). The reaction proceeds with good yields, under mild reaction conditions (40 °C) and large excess of substrate is not needed. In addition, excellent activity is observed in the cyclopropanation of challenging aliphatic olefins. (Figure presented.).
- Rodríguez, Mònica,Font, Gemma,Nadal-Moradell, Joel,Hernán-Gómez, Alberto,Costas, Miquel
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supporting information
p. 5116 - 5123
(2020/10/06)
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- Improving Catalyst Activity in Hydrocarbon Functionalization by Remote Pyrene–Graphene Stacking
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A copper complex bearing an N-heterocyclic carbene ligand with a pyrene “tail” attached to the backbone has been prepared and supported on reduced graphene oxide (rGO). The free and supported copper materials have been employed as homogeneous and heterogeneous catalysts in the functionalization of hydrocarbons such as n-hexane, cyclohexane, and benzene through incorporation of the CHCO2Et unit from ethyl diazoacetate. The graphene-anchored complex displays higher reaction rates and induces higher yields than its soluble counterpart, features that can be rationalized in terms of a decrease in electron density at the metal center due to a remote net electronic flux from the supported copper complex to the graphene surface.
- Ballestin, Pilar,Ventura-Espinosa, David,Martín, Santiago,Caballero, Ana,Mata, Jose A.,Pérez, Pedro J.
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p. 9534 - 9539
(2019/06/04)
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- Selective hydrogenation of α,β-unsaturated carbonyl compounds on silica-supported copper nanoparticles
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Silica-supported copper nanoparticles prepared via surface organometallic chemistry are highly efficient for the selective hydrogenation of various α,β-unsaturated carbonyl compounds yielding the corresponding saturated esters, ketones, and aldehydes in the absence of additives. High conversions and selectivities (>99%) are obtained for most substrates upon hydrogenation at 100-150 °C and under 25 bar of H2.
- Mendes-Burak, Jorge,Ghaffari, Behnaz,Copéret, Christophe
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supporting information
p. 179 - 181
(2019/01/04)
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- Blue light-promoted photolysis of aryldiazoacetates
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Aryldiazoacetates can undergo photolysis under blue light irradiation (460-490 nm) at room temperature and under air in the presence of numerous trapping agents, such as styrene, carboxylic acids, amines, alkanes and arenes, thus providing a straighforward and general platform for their mild functionalization.
- Jurberg, Igor D.,Davies, Huw M. L.
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p. 5112 - 5118
(2018/06/12)
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- Enhanced Electrophilicity of Heterobimetallic Bi-Rh Paddlewheel Carbene Complexes: A Combined Experimental, Spectroscopic, and Computational Study
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Dirhodium paddlewheel complexes are indispensable tools in modern organometallic catalysis for the controlled decomposition of diazo-compounds. Tuning the reactivity of the thus-formed transient carbenes remains an active and dynamic field of research. Herein, we present our findings that the distal metal center plays an as yet underappreciated role in modulating this reactivity. Replacement of one rhodium atom in the bimetallic core for bismuth results in the formation of a significantly more electrophilic carbene complex. Bismuth-rhodium catalysts thereby facilitate previously unknown modes of reactivity for α-diazoester compounds, including the cyclopropanation of alkenes as electron deficient as trichloroethylene. While dirhodium paddlewheel complexes remain the catalysts of choice for many carbene-mediated transformations, their bismuth-rhodium analogues exhibit complementary reactivity and show great potential for small molecule and solvent activation chemistry. DFT calculations highlight the importance of metal-metal bonding interactions in controlling carbene electrophilicity. The paucity of these interactions between the 4d orbitals of rhodium and the 6p orbitals of bismuth results in weaker π-back-bonding interactions for bismuth-rhodium carbene complexes compared to dirhodium carbene complexes. This leads to weakening of the rhodium-carbene bond and to a more carbene-centered LUMO, accounting for the observed enhancement in bismuth-rhodium carbene electrophilicity. These findings are supported by a detailed spectroscopic study of the "donor-donor" carbene complexes Rh2(esp)2C(p-MeOPh)2 (19) and BiRh(esp)2C(p-MeOPh)2 (20), employing a combination of UV-vis and resonance Raman spectroscopy. The results reveal that carbene chemoselectivity in MRh(L)4 catalysis can be modulated to a previously unrecognized extent by the distal metalloligand.
- Collins, Lee R.,Van Gastel, Maurice,Neese, Frank,Fürstner, Alois
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supporting information
p. 13042 - 13055
(2018/10/15)
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- Water as the Reaction Medium for Intermolecular C-H Alkane Functionalization in Micellar Catalysis
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A series of alkanes CnH2n+2 have been functionalized in water as the reaction medium, using a silver-based catalyst, upon the insertion of carbene (CHCO2Et from N2CHCO2Et) groups into the carbon-hydrogen bonds of hexane, cyclohexane, or 2-methylbutane, among others. The regioselectivity toward the distinct reaction sites is identical to that found in neat alkane, the water-based system allowing the use of a much shorter excess of the hydrocarbon. This is the first example of the intermolecular functionalization of alkanes with this strategy in water. The functionalized alkanes partially undergo the incorporation of a second carbene unit to provide α-(acyloxy)acetates, in an unprecedented tandem reaction of this nature.
- álvarez, María,Gava, Riccardo,Rodríguez, Manuel R.,Rull, Silvia G.,Pérez, Pedro J.
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p. 3707 - 3711
(2017/06/09)
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- CATALYST AND BATTERY COMPONENTS DERIVED FROM CONDENSATION REACTIONS WITH CARBA-CLOSO-DODECABORATE AMINES
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Described herein is the fusion of two families of unique carbon-containing molecules that readily disregard the tendency of carbon to form four chemical bonds, namely N-heterocyclic carbenes (NHCs) and carborane anions. Deprotonation of an anionic imidazolium salt with lithium diisopropylamide at room temperature leads to a mixture of lithium complexes of C-2 and C-5 dianionic NHC constitutional isomers as well as a trianionic (C-2, C-5) adduct. Judicious choice of the base and reaction conditions allows for the selective formation of all three stable polyanionic carbenes. In solution, the so-called abnormal C-5 NHC lithium complex slowly isomerizes to the normal C-2 NHC, and the process can be proton catalyzed by the addition of the anionic imidazolium salt. These results indicate that the combination of two unusual forms of carbon atoms can lead to unexpected chemical behavior, and that this strategy paves the way for the development of a broad new generation of NHC ligands for catalysis.
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Paragraph 0278
(2015/10/05)
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- Zinc(II)-Mediated Carbene Insertion into C-H Bonds in Alkanes
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The cationic zinc adduct {[HB(3,5-(CF3)2Pz)3]Zn(NCMe)2}ClO4 catalyzes the functionalization of tertiary, secondary, and primary C-H bonds of alkanes via carbene insertion. Ethyl diazoacetate serves as the:CHCO2Et carbene precursor. The counteranion, supporting ligand, and coordinating solvents affect the catalytic activity. An in situ generated {[HB(3,5-(CF3)2Pz)3]Zn}+ species containing a bulkier {B[3,5-(CF3)2C6H3]4}- anion gives the best results among the zinc catalysts used.
- Kulkarni, Naveen V.,Dash, Chandrakanta,Jayaratna, Naleen B.,Ridlen, Shawn G.,Karbalaei Khani, Sarah,Das, Animesh,Kou, Xiaodi,Yousufuddin, Muhammed,Cundari, Thomas R.,Dias, H. V. Rasika
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supporting information
p. 11043 - 11045
(2015/12/17)
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- A fully recyclable heterogenized Cu catalyst for the general carbene transfer reaction in batch and flow
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A polystyrene-linked tris(triazolyl)methanecopper(i) cationic catalyst operates under heterogeneous conditions for the reaction of ethyl diazoacetate (EDA) with an array of substrates. Carbon-hydrogen as well as X-H (X = O, N) functionalization derived from the formal transfer of the carbene moiety (:CHCO2Et) from the copper center and subsequent insertion have been achieved, the reactions permitting repeated catalyst recycling and reuse. The addition of the same carbene unit to benzene leading to a cycloheptatriene derivative (Büchner reaction) or to phenylacetylene (cyclopropenation) took place at similar rates to the insertion processes and with the same catalyst recyclability. The use of this heterogenized cationic Cu catalyst in continuous flow has also been implemented. Key characteristics of the flow process are its high and constant turnover frequency (TOF) (residence times of 1 min still lead to full conversion in the reaction with ethanol after 48 h operation) and its suitability for the sequential performance of different types of carbene transfer reactions with a simple and affordable experimental setup.
- Maestre, Lourdes,Ozkal, Erhan,Ayats, Carles,Beltrn, lvaro,Daz-Requejo, M. Mar,Prez, Pedro J.,Perics, Miquel A.
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p. 1510 - 1515
(2015/02/05)
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- Efficient microwave-assisted esterification reaction employing methanesulfonic acid supported on alumina as catalyst
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A rapid and efficient protocol assisted by microwave irradiation for the synthesis of esters using methanesulfonic acid (CH3SO3H) supported on Al2O3 (AMA) as catalyst and free of solvent is described. The products were obtained in good yields and purity, with reduced reaction time, and the process is simple and environmentally benign. Copyright
- Fabian, Lucas,Gomez, Matias,Kuran, Juan A. Caturelli,Moltrasio, Graciela,Moglioni, Albertina
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p. 2386 - 2392
(2014/07/22)
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- Catalytic, enantioselective, and highly chemoselective bromocyclization of olefinic dicarbonyl compounds
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Overriding preferences: An amine-thiocarbamate catalyst can mediate the facile, efficient, and highly enantioselective bromocyclization of olefinic 1,3-dicarbonyl compounds. In the presence of the bifunctional catalyst, the bromination occurs chemoselectively at the olefinic moiety rather than at the carbon atom in the α-position to the carbonyl units. Copyright
- Zhao, Yi,Jiang, Xiaojian,Yeung, Ying-Yeung
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p. 8597 - 8601
(2013/09/12)
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- Copper hydride-catalyzed reduction of electron-deficient olefins
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Copper hydride derived from CuF(PPh3)3·2MeOH- bis[(2-diphenylphosphino)phenyl] ethersilane can reduce electron-deficient olefins selectively and efficiently.
- Zheng, Ai-Jun,Shan, Feng-Jun,Li, Zheng-Ning,Li, Zeng-Chang,Jiang, Lan
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p. 1271 - 1276
(2013/07/19)
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- Intermetallic coinage metal-catalyzed functionalization of alkanes with ethyl diazoacetate: Gold as a ligand
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The complexes [Au2M2(C6F5) 4(NCMe)2]n (M = Cu, 1; M = Ag, 2) have been tested as catalysts for the functionalization of alkanes by the carbene insertion methodology, using ethyl diazoacetate as the carbene source. Moderate to high conversions have been obtained. The observed selectivities seem to favor the proposal that the active metal for catalysis is the Cu/Ag center, the Au(C6F5)2 unit acting as a spectator ligand in both cases.
- Fuentes, M. ángeles,Rodríguez-Castillo, María,Monge, Miguel,Olmos, M. Elena,López-De-Luzuriaga, Jose M.,Caballero, Ana,Pérez, Pedro J.
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experimental part
p. 146 - 149
(2011/06/22)
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- Reactions of CF3-substituted boranes with α-diazocarbonyl compounds
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Boranes substituted with a CF3-group can be generated from methyl boronic esters RB(OMe)2 and Me3SiCF3/KF followed by treatment with Me3SiCl. These boranes are stable only in coordinating solvents, and due to the increased Lewis acidity of boron, react rapidly with α-diazocarbonyl compounds to give the products of transfer of the organic group from boron. Alkyl, aryl, vinyl, and alkynyl boronic esters can be used in this reaction.
- Elkin, Pavel K.,Levin, Vitalij V.,Dilman, Alexander D.,Struchkova, Marina I.,Belyakov, Pavel A.,Arkhipov, Dmitry E.,Korlyukov, Alexander A.,Tartakovsky, Vladimir A.
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supporting information; experimental part
p. 5259 - 5263
(2011/10/31)
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- Synthesis of new copper(i) complexes with tris(2-pyridyl) ligands. Applications to carbene and nitrene transfer reactions
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New copper(i) complexes with tris(2-pyridyl)methane (TPC), tris(2-pyridyl)methoxymethane (TPM) and tris(2-pyridyl)amine (TPN) ligands have been synthesized and characterized, including structural determinations by X-ray diffraction of some examples. Their activity as catalysts in carbene and nitrene transfer reactions was studied.
- Perez, Julio,Morales, Dolores,Garcia-Escudero, Luis A.,Martinez-Garcia, Hector,Miguel, Daniel,Bernad, Pablo
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scheme or table
p. 375 - 382
(2009/04/14)
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- Rhodium/graphite-catalyzed hydrogenation of carbocyclic and heterocyclic aromatic compounds
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Rhodium on graphite (Rh/Gr, C24Rh) was prepared by reaction of anhydrous rhodium trichloride with potassium graphite (C8K, 3 equivalents) and used as a heterogeneous catalyst for the hydrogenation of carbocyclic and heterocyclic aromatic compounds at room temperature and 1 atm of hydrogen pressure. The effect of substitution on the benzene ring was examined in a variety of derivatives, including those with alkyl, hydroxy, alkoxy, aryloxy, carboxy, amino, nitro, acyl, chloro, or functionalized alkyl groups. Reduction of carbonyl functions of aromatic aldehydes and ketones occurred with complete or partial cleavage of the benzylic C-O bond; this cleavage also occurred in the hydrogenation of benzylic alcohols and esters. Georg Thieme Verlag Stuttgart.
- Falini, Giuseppe,Gualandi, Andrea,Savoia, Diego
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experimental part
p. 2440 - 2446
(2010/02/27)
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- The effect of catalyst loading in copper-catalyzed cyclohexane functionalization by carbene insertion
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A study of the variables that affect the insertion of the :CHCO 2Et group (formed from ethyl diazocetate, EDA) into the C-H bonds of cyclohexane in the presence of a TpxCu complex as the catalyst (Tpx = trispyrazolylborate ligand) has demonstrated an anomalous effect of the catalyst loading. The use of low concentrations of catalyst produces an increase in the yield of the C-H activation product ethyl cyclohexaneacetate. This effect has also been found in the case of other less elaborated catalysts such as [BpBr3Cu] or [(bipy)2-Cu][I]. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.
- Caballero, Ana,Diaz-Requejo, M. Mar,Trofimenko, Swiatoslaw,Belderrain, Tomas R.,Perez, Pedro J.
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p. 2848 - 2852
(2008/02/10)
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- Very efficient, reusable copper catalyst for carbene transfer reactions under biphasic conditions using ionic liquids
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The complex {[HC(3,5-Me2pz)3]Cu(NCMe)}BF4 catalyzes the transfer of the :CHCO2Et unit from ethyl diazoacetate to several saturated and unsaturated substrates with very high yields and under biphaslc conditions using the ionic liquid [bmim][PF6] and hexane as the reaction medium. The catalyst has been tested for several cycles of recovery and reuse without any loss of activity.
- Rodriguez, Pilar,Caballero, Ana,Diaz-Requejo, M. Mar,Nicasio, M. Carmen,Perez, Pedro J.
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p. 557 - 560
(2007/10/03)
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- Intermolecular copper-catalyzed carbon-hydrogen bond activation via carbene insertion
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A series of catalysts of general formula TpXCu (TpX = homoscorpionate ligand) promote the insertion of :CHCO2Et (ethyl diazoacetate as the carbene source) into the C-H bonds of cycloalkanes and cyclic ethers in moderate to high yield. A correlation between the steric hindrance of these catalysts and the yield of the transformation has been observed. Copyright
- Diaz-Requejo, M. Mar,Belderrain, Tomas R.,Nicasio, M. Carmen,Trofimenko, Swiatoslaw,Perez, Pedro J.
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p. 896 - 897
(2007/10/03)
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- Effect of carbenoid structure on the reactivity of rhodium-stabilized carbenoids
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The outcome of rhodium(II) pivalate catalyzed decomposition of diaozoacetates in the presence of cyclohexane is highly dependent on carbenoid structure. Carbenoids derived from phenyldiazoacetates or diazoketoesters undergo high yielding intermolecular C-H insertions while other carbenoid systems undergo rearrangements, dimerization or trimerization.
- Davies, Huw M. L.,Hodges, L. Mark,Matasi, Julius J.,Hansen, Tore,Stafford, Douglas G.
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p. 4417 - 4420
(2007/10/03)
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- Conversion of 2-methylthio-4-trifluoroacetyl-5,6-dihydro-4H-1,3,4-thiadiazines intoα,β-unsaturated esters via carbanion-induced ring opening and desulfurization
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A convenient conversion of 2-methylthio-5,6-dihydro-4H-1,3,4-thiadiazines 1 into α,β-unsaturated esters was achieved through the procedure including trifluoroacetylation of 1, carbanion-induced ring opening of trifluoroacetamides 2, and reductive removal of heteroatom functionality of the resulting S-alkenyl hydrazinecarbodithioates 3. Treatment of 3 with a base under an aqueous condition also gave the corresponding 6-alkylidene-4H-1,3,4-thiadiazin-5-ones 6.
- Shimada, Kazuaki,Otaki, Akihiro,Yanakawa, Masaki,Mabuchi, Shosuke,Yamakado, Naoya,Shimoguchi, Takeshi,Takikawa, Yuji
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p. 329 - 330
(2007/10/03)
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- Tin-free reductive photochemical carboxymethylation of olefins with α- alkylthioacetates
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An efficient tin-free reductive photochemical carboxymethylation of olefins with α-alkylthioacetates is developed, which (a) is an experimentally simple technique furnishing substituted derivatives of fatty acids in moderate to good yields, (b) is compatible with polar/protic functional groups and solvents, (c) does not require a special reducing reagent, (d) is fairly insensitive to the presence of dissolved oxygen and, generally, does not require degassing prior to irradiation. The critical feature of the mechanism is the 'reluctance' of short-lived MeS' to group- transfer, resulting in hydrogen abstraction from the media.
- Deng, Lisa X.,Kutateladze, Andrei G.
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p. 7829 - 7832
(2007/10/03)
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- A short and efficient enantioselective synthesis of cyclohexylnorstatine, a key component of a renin inhibitor
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A catalytic asymmetric synthesis of ethyl (2R,35)-N-(p- toluenesulfonyl)-3-amino-4-cyclohexyl-2-hydroxybutyrate 7 in 96% ee from cheaply available cyclohexanone is described employing Sharpless asymmetric aminohydroxylation as the key step.
- Upadhya,Sudalai
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p. 3685 - 3689
(2007/10/03)
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- Electrochemical deacetylation of 1,3-dicarbonyl compounds
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Mild deacetylation of 1,3-dicarbonyl compounds was achieved by halonium-ion mediated electrolysis. In this reaction, the supporting electrolyte including sodium halide NaX (X = Cl or Br) was essential since the reaction proceeded through substitution by a halonium ion, generated electrochemically at anode, on active methine carbons followed by base-aitalyzed deacctylation, and was terminated by reductive dehalogenation of the formed α-halo carbonyl compounds at cathode.
- Fujimoto, Kazuo,Maekawa, Hirofumi,Matsubara, Yoshiharu,Nishiguchi, Ikuzo
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p. 143 - 144
(2007/10/03)
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- The Invention of Radical Reactions. XXXIII Homologation Reactions of Carboxylic Acids by Radical Chain Chemistry
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Various carbon radicals can be generated from carboxylic acids via the corresponding Barton esters.These radicals can be used for the synthesis of longer chain homologues of the original acids.
- Barton, Derek H. R.,Chern, Ching-Yuh,Jaszberenyi, Joseph Cs.
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p. 407 - 426
(2007/10/02)
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- Chain-elongation and Degradation of Carboxylic Acids by Barton-ester Based Radical Chemistry
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The reaction of α-trifluoroacetoxy acrylates and acrylonitriles with carbon radicals formed from carboxylic acids gives adducts that can be transformed into vic-diols, esters, amides, and homoaldehydes in good to high yield.Aldoses can be smoothly degraded to the corresponding nor- or bis-nor compounds using radical chemistry.
- Barton, Derek H. R.,Chern, Ching-Yuh,Jaszberenyi, Joseph Cs.,Shinada, Tetsuro
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p. 6505 - 6508
(2007/10/02)
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- Ester Homologation Revisited: A Reliable, Higher Yielding and Better Understood Procedure
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Enolate anions 3 and 6, prepared via enolization of α-bromo and dibromo ketones 4 and 5 were converted in high yield to ynolate anions 10 by respective addition of lithium tetramethylpiperidide (to effect deprotonation, 3 --> 7) or butyllithium (to effect metal-halogen exchange, 6 --> 7).Mixtures of such enolates were also obtainable from esters 1 on a large-scale (25 mmol) via in situ formation and addition of lithiodibromomethane (from methylene bromide and lithium tetramethylpiperidide), followed by treatment of the resulting adducts with lithiumhexamethyldisilazide to ensure complete enolization.Addition of sec-butyllithium and n-butyllithium to effect ynolate anion formation, followed by quenching of the reaction mixtures into acidic ethanol, reproducibly afforded homologated esters 8 in 67-90percent yield.Demonstrated for ethyl esters 1 having the carbethoxy moiety attached to primary, secondary, tertiary, aryl, and alkenyl groups, this general procedure provides a convenient, large-scale alternative to the classical Arndt-Eistert sequence.
- Kowalski, Conrad J.,Reddy, Rajarathnam E.
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p. 7194 - 7208
(2007/10/02)
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- Insights into the Electrochemical Reductive Cyclization of α,β-Unsaturated Carbonyl Derivatives
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A series of acyclic and cyclic α,β-unsaturated esters bearing tethered mesylate leaving groups have been electrochemically reduced to give synthetically useful yields of monocyclic and bicyclic esters via attack of the β-carbon of the α,β-unsaturated ester on the carbon bearing the mesylated moiety.
- Gassman, Paul G.,Lee, Changjin
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p. 2175 - 2178
(2007/10/02)
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- Peptide immunostimulants
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Peptide compounds of formula 1, pharmaceutically acceptable base salts thereof, pharmaceutical compositions and their use as antiinfective agents where R1 is alkyl, cycloalkyl or cycloalkylmethyl; R2 is hydrogen or alkyl and R3 is hydroxy or an amino acid residue of the formula where X is hydrogen, alkyl or hydroxymethyl and nis an integer of 0 to 4 and R4 and R5 are alkyl, hydrogen, benzyl or cyclohexylmethyl.
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- The decomposition of ethyl diazoacetate over zeolite NaCuX
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The decomposition of ethyl diazoacetate catalyzed by Cu(II)-exchanged zeolite NaX, has been studied.Catalytic activity required at least 25 percent sodium exchange of the zeolite.From 25 percent exchange to higher levels the decomposition rate increased linearly with the copper introduced into the zeolite.With cyclohexane as the solvent, the (ethoxycarbonyl)carbene formed was found to yield dimers, diethyl maleate and diethyl fumarate, and also compounds resulting from reaction with the solvent or with residual water present in the zeolite.Reduction of Cu(II) to Cu(I) increased the activity of the catalysts.The degree of hydration of the zeolite had a large effect on the activity of the catalyst and on the selectivity of the reaction.Complexation of the Cu(II) ions with NH3 or 1,2-propanediamine reduced the activity of the zeolite drastically.Zeolite NaCuX showed no induction time in contrast to several copper salts tested.
- Oudejans, J. C.,Kaminska, J.,Bekkum, H. van
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p. 537 - 541
(2007/10/02)
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- HOMOLOGATION OF N-ALKANES USING DIAZOESTERS AND RHODIUM(III)PORPHYRINS. ENHANCED ATTACK ON PRIMARY C-H BONDS.
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Carbethoxycarbene, from ethyl diazoacetate and rhodium(III)porphyrins, inserted into methyl C-H bonds of n-alkenes (C6 to C12) with yields up to 20-25 percent corresponding to a large increase of the primary/secondary selectivity.
- Callot, H.J.,Metz, F.
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p. 4321 - 4324
(2007/10/02)
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- Type II Photoelimination from α-Cycloalkylacetophenones and a Polystyrene-Bound Analogue
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In order to evaluate the effects of polymer binding on photoreactivity and other photochemical properties, we have synthesized α-cyclohexyl-p-methylacetophenone (I), α-cyclopentylacetophenone (II), and an analogue bound to insoluble polystyrene beads (P-I).All undergo type II photoelimination and are effective in energy transfer to an added quencher, trans-stilbene.Quantitative comparisons show that the polymer binding has little effect upon the photoreactivity as long as the polymer is in a swelling solvent, such as pentane, which allows the necessary molecular flexibility.The efficiency of energy transfer is somewhat reduced upon polymer binding.
- Wamser, Carl C.,Wagner, William R.
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p. 7232 - 7234
(2007/10/02)
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