- Catalytic asymmetric carbon-carbon bond forming reactions: Preparation of optically enriched 2-aryl propionic acids by a catalytic asymmetric hydroboration-homologation sequence
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A new catalytic asymmetric one-carbon homologation strategy has been developed which employs a rhodium catalyzed asymmetric hydroboration followed by homologation with LiCHCl2 and oxidation to generate 2-arylpropionic acids of high enantiomeric purity.
- Chen, Austin C.,Ren, Li,Crudden, Cathleen M.
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Read Online
- Redox switchable catalysis utilizing a fluorescent dye
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This report describes the implementation of a 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) dye into the ligand framework of a Rh-based catalyst. The redox-active nature of the BODIPY dye is utilized to generate a catalyst that is capable of exhibit
- Heiden, Zachariah M.,Simons, Casey R.,Thompson, Brena L.
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Read Online
- Homologation Strategy for the Generation of 1-Chloroalkyl Radicals from Organoboranes
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The generation of 1-bromo and 1-chloroalkyl radicals from organoboranes has been investigated. The direct approach involving the hydroboration of halogenated alkenes is impeded by partial dehalogenation taking place during the hydroboration process. An indirect method involving the generation of B-(1-chloroalkyl)catecholborane by homologation of B-alkylcatecholborane with dichloromethyllithium was developed. A reaction sequence involving a hydroboration reaction, a Matteson homologation, and a radical allylation process has been performed as a one-pot process that takes advantage of three different reactivities of organoboron species. Starting from styrene derivatives, it was possible to prepare B-(1-chloro-2-arylpropyl)catecholboranes that are excellent precursors to 1-chloro-2-arylpropyl radicals. A concise approach for the synthesis of an optically active α-methylene-γ-lactone from p-chlorostyrene has been developed on the basis of a two-step sequence involving an enantioselective hydroboration-homologation-cyclization reaction followed by a hydrolysis-lactonization process. (Chemical Equation Presented).
- Xu, Gong,Lüthy, Monique,Habegger, Jacqueline,Renaud, Philippe
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p. 1506 - 1519
(2016/03/01)
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- Electronic tuning of a carbene center via remote chemical induction, and relevant effects in catalysis
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The present report develops the idea that an N-heterocyclic carbene incorporating a remote anionic functionality-here, a malonate group-as a backbone component of its heterocy- clic framework, can be post-function- alized directly from its transition- metal complexes, upon simple addition of a variety of electrophiles interacting directly with the malonate group in the outer coordination sphere. From a palette of selected electrophilic reagents, it was thus possible to modulate the electronic donor properties of the car- bene center over a rather broad range. Both the zwitterionic complex [Rh{malo-NHCj(cod)] and the cationic derivatives [Rh{malo-NHCE}(cod)] + (where ma/o-NHCE represents the ligand modified by a selected electro- phile E ) were used as pre-catalysts in two types of catalytic reactions, namely, the polymerization of phenyl- acetylene and the hydroboration of styrene. The results indicate that, in both cases, the zwitterionic species is by far the best catalyst, whereas a decrease in the ligand donicity induced by the added electrophile results in a concomitant reduction of catalytic activity. Apparent deviations to such a trend in the case of the hydroboration of styrene were rationalized in terms of an interaction between the reactive catechol- borane substrate and the remote functionality of the N-heterocyclic carbene leading to an in situ modification of the nature of the active species. These observations serve as a useful basis to define the scope and limitations of the present conceptual approach in catalysis.
- Cesar, Vincent,Lugan, Noel,Lavigne, Guy
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experimental part
p. 11432 - 11442
(2010/11/24)
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- Gold(0) nanoparticles for selective catalytic diboration
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Going with gold: Gold(0) nanoparticles stabilized with the diphosphine ligand binap mediate the catalytic diboration of styrene, resulting in complete formation of the bis(boronate)ester product. The gold(0) catalytic mechanism can involve base-assisted h
- Ramirez, Jesus,Sanau, Mercedes,Fernandez, Elena
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supporting information; experimental part
p. 5194 - 5197
(2009/04/11)
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- Metal catalysed hydroboration of vinyl sulfides, sulfoxides, sulfones, and sulfonates
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The hydroboration of phenyl vinyl sulfide with catecholborane (HBcat) and pinacolborane (HBpin) has been examined with a number of rhodium complexes, all of which proceed with excellent regiocontrol in favour of the branched product PhSCH(B(OR)2)CH3. The corresponding linear product can be obtained exclusively in reactions employing [Cp*IrCl2]2 and HBcat. Catalysed hydroborations of (E)-2-(p-toluenethio)styrene with HBcat using Rh(acac)(dppp) gave predominant formation of one product while reactions using HBpin afforded several products arising from a competing C-S bond cleavage (acac = acetylacetonato, dppp = 1,3-bis(diphenylphosphino)propane). Although reactions of phenyl vinyl sulfoxide were complicated by a competing deoxygenation reaction, hydroborations of phenyl vinyl sulfone using HBcat once again gave regioselective formation of either the branched or linear products, depending on the choice of catalyst used to effect this transformation. Catalysed hydroborations of phenyl vinyl sulfonate were less chemo- and regioselective, yielding hydrogenation and diboration products in addition to the two hydroboration product isomers.
- Webb, Jonathan D.,Harrison, Daniel J.,Norman, David W.,Blacquiere, Johanna M.,Vogels, Christopher M.,Decken, Andreas,Bates, Craig G.,Venkataraman,Baker, R. Thomas,Westcott, Stephen A.
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- A valuable, inexpensive CuIN-heterocyclic carbene catalyst for the selective diboration of styrene
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The complexes [Cu(NHC)(NCMe)]BF4 (NHC = N-heterocyclic ligand), with bis(catecholato)diboron (B2(cat)2) as the boron source, efficiently catalyze the diboration of styrene with very high degrees of conversion. With the appropriate NHC ligand, the reaction proceeds quantitatively toward the diborated derivative PhCH(Bcat)-CH2(Bcat). The [styrene]/[B2(cat)2] ratio also has a strong effect on the selectivity: the use of an excess of styrene allows modification of the selectivity toward the formation solely of the monoborated derivative. PhCH 2-CH2(Bcat). DFT calculations suggest that no oxidative addition processes take place at copper, hut that intermediates containing coordinated σ-bonds are involved in the catalytic cycle.
- Lillo, Vanesa,Fructos, Manuel R.,Ramirez, Jesus,Braga, Ataualpa A. C.,Maseras, Feliu,Diaz-Requejo, M. Mar,Perez, Pedro J.,Fernandez, Elena
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p. 2614 - 2621
(2008/04/01)
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- Zwitterionic relatives to the classic [(P-P)Rh(solv)2]+ ions: Neutral catalysts active for H-E bond additions to olefins (E = C, Si, B)
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Formally zwitterionic bis(phosphanyl)-and bis(amino)borate rhodium(1) complexes (see picture) can catalytically mediate the hydrogenation, hydroacylation, hydroboration, and hydrosilation of double bonds. These neutral systems are shown to be highly active, even under conditions incompatible with their isostructural, but formally cationic, relatives.
- Betley, Theodore A.,Peters, Jonas C.
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p. 2385 - 2389
(2007/10/03)
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- Catalytic asymmetric hydroboration/amination and alkylamination with rhodium complexes of 1,1′-(2-diarylphosphino-1-naphthyl)isoquinoline
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Catecholboronate esters formed by asymmetric hydroboration of arylalkenes are not directly converted to amines by reaction with hydroxylamine-O-sulfonic acid. Prior conversion to a trialkylborane by reaction with ZnEt2 or MeMgCl permits a subsequent amination reaction to occur with essentially complete retention of configuration, leading to a range of primary α-arylalkylamines in up to 97% enantiomeric excess (ee). Secondary, but not tertiary amines may be formed by a related pathway when in situ generated alkylchloramines are employed as the aminating agent. The catalytic asymmetric hydroboration, β-alkylation and amination steps may be combined in a single stage. Overall, this provides a practical procedure for the synthesis of enantiomerically enriched arylamines, exemplified inter alia by the synthesis of (S)-1,2,3,4-tetrahydro-1-naphthylamine in 95-97% ee and of (R)-N-(cyclohexyl)-1′-(4-methoxyphenyl)ethylamine in 93 % ee.
- Fernandez, Elena,Maeda, Kenji,Hooper, Mark W.,Brown, John M.
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p. 1840 - 1846
(2007/10/03)
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