- Regiodivergent DH or HD Addition to Alkenes: Deuterohydrogenation versus Hydrodeuterogenation
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The regioselective and regiodivergent addition of H-D to a variety of 1,1-diarylalkenes was realized utilizing selectively deuterated dihydroaromatic compounds, which were generated by cobalt catalysis. The reaction was initiated by catalytic amounts of B
- Hilt, Gerhard,Li, Luomo
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supporting information
(2020/03/03)
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- SBA-15/POSS-Imidazolium Hybrid as Catalytic Nanoreactor: the role of the Support in the Stabilization of Palladium Species for C?C Cross Coupling Reactions.
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Supported imidazolium modified polyhedral oligomeric silsesquioxanes (POSS) on SBA-15 have been used as platform for Pd(II) species. The so-obtained material was firstly characterized by means of TGA, solid state NMR, TEM, XPS, SAXS, porosimetry and ICP-OES and it was successfully tested as pre-catalyst in C?C cross couplings, namely Suzuki-Miyaura and Heck reactions. In both cases, the solid proved to be highly efficient and easily recoverable from the reaction mixture. The recyclability was verified for up to seven cycles without showing any activity decrease. Interestingly, only Pd(II) was detected in the reused catalyst in the Heck reaction. Therefore, the versatility of the material was investigated by using various aryl halides. Our palladium nanocomposite was able to promote both Suzuki and Heck reactions down to 0.0007 mol% showing outstanding turnover frequency (TOF) values of 114,286 and 32,381 h?1, respectively. Comparison with the palladium catalyst on SiO2-POSS-imidazolium support showed interesting differences in terms of stabilization of Pd species and recyclability. The excellent outcome of the reactions could be ascribed to the textural properties of the SBA-15 support and the presence of the imidazolium-POSS nanocage within the pores of SBA-15, that worked as a sort of nanoreactor. (Figure presented.).
- Calabrese, Carla,Campisciano, Vincenzo,Siragusa, Fabiana,Liotta, Leonarda F.,Aprile, Carmela,Gruttadauria, Michelangelo,Giacalone, Francesco
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p. 3758 - 3767
(2019/05/15)
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- Regioselective Transfer Hydrodeuteration of Alkenes with a Hydrogen Deuteride Surrogate Using B(C6F5)3 Catalysis
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A regioselective hydrodeuteration of alkenes using monodeuterated cyclohexa-1,4-dienes as surrogates for hydrogen deuteride (HD) gas is reported. The metal-free process proceeds under B(C6F5)3 catalysis presumably by deuteride abstraction to form borodeuteride [DB(C6F5)3]a and highly Br?nsted-acidic Wheland intermediates. Low catalyst loadings (2.5 mol %) are used, and the reaction proceeds at room temperature.
- Walker, Johannes C. L.,Oestreich, Martin
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supporting information
p. 6411 - 6414
(2018/10/20)
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- Metal-free oxidative cross-coupling of diazirines with arylboronic acids
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We report herein a metal-free cross-coupling of diazirines with arylboronic acids under oxidative conditions. The reaction affords a series of substituted olefins. It is proposed that the interaction between the nitrogen on diazirine with arylboronic acid plays a key role in this transformation.
- Wu, Guojiao,Zhao, Xia,Ji, Wenzhi,Zhang, Yan,Wang, Jianbo
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p. 1961 - 1963
(2016/02/05)
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- Branched Arylalkenes from Cinnamates: Selectivity Inversion in Heck Reactions by Carboxylates as Deciduous Directing Groups
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A decarboxylative Mizoroki–Heck coupling of aryl halides with cinnamic acids has been developed in which the carboxylate group directs the arylation into its β-position before being tracelessly removed through protodecarboxylation. In the presence of a copper/palladium catalyst, both electron-rich and electron-deficient aryl bromides and chlorides bearing numerous functionalities were successfully coupled with broadly available cinnamates, with selective formation of 1,1-disubstituted alkenes. This reaction concept, in which the carboxylate acts as a deciduous directing group, ideally complements traditional 1,2-selective Heck reactions of styrenes.
- Tang, Jie,Hackenberger, Dagmar,Goossen, Lukas J.
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supporting information
p. 11296 - 11299
(2016/10/13)
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- Well-defined palladium(0) complexes bearing N-heterocyclic carbene and phosphine moieties: Efficient catalytic applications in the Mizoroki-Heck reaction and direct C-H functionalization
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Two series of well-defined palladium(0) complexes with phosphine-functionalized N-heterocyclic carbene ligands were prepared. These complexes featured six- and seven-membered chelate rings in the two series. Among the seven-membered chelate complexes, those featuring the PCy2 moiety exhibited observable fluxional behavior on the NMR time scale, corresponding to the interchange between two sets of conformations. Most of these novel complexes were successfully structurally characterized by single-crystal X-ray diffraction studies. These two series of palladium(0) complexes were tested for their potential catalytic applications in two mechanistically distinct reactions, namely, Mizoroki-Heck coupling and direct C-H functionalization reactions. One of the six-membered chelate complexes was found to be an efficient pre-catalyst for mediating the coupling reactions between aryl chlorides and alkenes. The palladium(0) complex could also be effectively applied in the direct C-H functionalization reactions of aryl bromides with 1,2-dimethylimidazole.
- Lee, Jhen-Yi,Shen, Jiun-Shian,Tzeng, Ru-Jiun,Lu, I-Chen,Lii, Jenn-Huei,Hu, Ching-Han,Lee, Hon Man
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p. 10375 - 10388
(2016/07/06)
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- Evidences of release and catch mechanism in the Heck reaction catalyzed by palladium immobilized on highly cross-linked-supported imidazolium salts
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Palladium (10 wt%) on a highly cross-linked imidazolium-based material was used as catalyst in 0.1 mol% in the Heck reaction between several alkenes and aryl iodides. Products were obtained from good to high yields. Deeper investigations showed a release of Pd species in solution and their capture by the imidazolium-based support. When a sixfold amount of support was employed the re-captured Pd species (0.5-0.6 wt%) were not anymore catalytically active. This result represents a new interesting aspect of this work since the highly cross-linked imidazolium-based material can act also as Pd scavenger avoiding the release of the metal in solution. Important differences between Heck and Suzuki reactions have been evidenced when the reactions were carried out in the presence of the scavenging support.
- Pavia, Cinzia,Giacalone, Francesco,Bivona, Lucia Anna,Salvo, Anna Maria Pia,Petrucci, Chiara,Strappaveccia, Giacomo,Vaccaro, Luigi,Aprile, Carmela,Gruttadauria, Michelangelo
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- Selective arylation and vinylation at the α position of vinylarenes
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In intermolecular Heck reactions of styrene and vinylarenes, the aryl and vinyl groups routinely insert at the β position. However, selective insertion at the α position has been very rare. Herein, we provide a missing piece in the palette of Heck reaction, which gave >20:1 α selectivity. The key to our success is a new ferrocene 1,1′-bisphosphane (dnpf) that carries 1-naphthyl groups. Our mechanistic studies revealed that the high α selectivity is partly attributable to the steric effect of dnpf. The rigid and bulky 1-naphthyl groups of dnpf sterically disfavor β insertion. What the Heck! In intermolecular Heck reactions, insertion at the β position of aromatic olefins is very common, but reversal of the selectivity for selective α insertion has been a longstanding problem. A general method to couple aryl and vinyl triflates with aromatic olefins in >20:1 α selectivity is presented. The key to this successful approach is a new ferrocene bisphosphane with naphthyl groups on the phosphorus atom (see scheme; OTf=triflate). Copyright
- Zou, Yinjun,Qin, Liena,Ren, Xinfeng,Lu, Yunpeng,Li, Yongxin,Zhou, Jianrong
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p. 3504 - 3511
(2013/07/05)
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- Distinctive meta-directing group effect for iridium-catalyzed 1,1-diarylalkene enantioselective hydrogenation
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An iridium-catalyzed asymmetric hydrogenation of 1,1-diarylkenes is described. Employing a novel, modular phosphoramidite ligand, PhosPrOx, in this transformation affords biologically relevant 1,1-diarylmethine products in good enantiomeric ratios (96.5:3
- Bess, Elizabeth N.,Sigman, Matthew S.
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p. 646 - 649
(2013/04/10)
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- Palladium catalyzed coupling of tosylhydrazones with aryl and heteroaryl halides in the absence of external ligands: Synthesis of substituted olefins
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Palladium catalyzed cross-coupling reaction of hydrazones with aryl halides in the absence of external ligand is reported. The versatility of this coupling reaction is demonstrated in showcasing the selectivity of coupling reaction in the presence of hydr
- Ojha, Devi Prasan,Prabhu, Kandikere Ramaiah
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p. 11027 - 11033
(2013/02/22)
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- Selective cine substitution of 1-arylethenyl acetates with arylboron reagents and a diene/rhodium catalyst
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When the crowd says Bo: A carbon-carbon bond is selectively formed at the β position of 1- arylethenyl acetate when the alkenyl substrate is reacted with arylboronic acids in the presence of a cycloocta-1,5-diene/rhodium catalyst. The choice of the ligand is crucial for the unusual cine substitution. Copyright
- Yu, Jung-Yi,Shimizu, Ryosuke,Kuwano, Ryoichi
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supporting information; experimental part
p. 6396 - 6399
(2010/11/17)
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- Pd-catalyzed oxidative cross-coupling of N-tosylhydrazones with arylboronic acids
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The Pd-catalyzed reaction of N-tosylhydrazones and arylboronic acids provides olefin derivatives. This oxidative cross-coupling is suggested to proceed through a migratory insertion process of a Pd carbene intermediate.
- Zhao, Xia,Jing, Jing,Lu, Kui,Zhang, Yan,Wang, Jianbo
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supporting information; experimental part
p. 1724 - 1726
(2010/07/06)
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- Atom-efficient vinylic arylations with triarylbismuths as substoichiometric multicoupling reagents under palladium catalysis
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The first atom-efficient arylation of vinylic iodides was achieved by using triarylbismuths as substoichiometric multicoupling reagents under palladium catalysis. Vinylic iodides were efficiently coupled with electronically divergent triarylbismuths to furnish the corresponding arylated products in short reaction times.
- Rao, Maddali L.N.,Jadhav, Deepak N.,Venkatesh, Varadhachari
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experimental part
p. 4300 - 4306
(2011/02/24)
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- Nonlinear solvent water effects in the excited-state (formal) intramolecular proton transfer (ESIPT) in m-hydroxy-1,1-diaryl alkenes: Efficient formation of m-quinone methides
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The photohydration of hydroxy-substituted 1,1-diaryl alkenes 1-3 has been studied in aqueous CH3CN solution. Evidence for formation of quinone methide intermediates was provided by product studies and by observation of its absorption spectrum by laser flash photolysis. For the meta isomers, the proposed mechanism of m-quinone methide formation probably involves a solvent-mediated ("proton-relay") excited-state (formal) intramolecular proton transfer (ESIPT) from the phenol hydroxyl group to the β-carbon of the alkene moiety in neutral aqueous CH3CN solution, either in a concerted manner or via two very fast steps. The m-quinone methides are then trapped by water to form the corresponding diaryl ethanol product with high overall quantum yield. Evidence for the ESIPT pathway was provided by fluorescence and LFP measurements. The addition of small amounts of water (3CN) decreased the fluorescence emissions of 1 and 2 with a concomitant increase in production of m-quinone methides. Stem-Volmer analyses of fluorescence data revealed a dynamic and a minor static quenching component, both of which involved a water trimer cluster. The degree of charge transfer from the phenol (phenolate) oxygen to the alkene β-carbon, which may be thought of as the driving force for this efficient ESIPT, is pronounced for the meta isomer in the excited state, consistent with Zimmerman's "meta-ortho effect". Alkenes 1 and 2 were shown to be more efficient in m-quinone methide photogeneration than the hydroxy-substituted benzyl alcohol 8, which required conditions of higher water content for similar quantum yields.
- Fischer, Maike,Wan, Peter
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p. 4555 - 4562
(2007/10/03)
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- The effect of meta- and para-methoxy substitution on the reactivity of the radical cations of arylalkenes and alkanes. Radical ions in photochemistry. Part 26
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The effect of meta- and para-methoxy substitution on the reactivity of some radical cations has been determined.The compounds chosen for study were 1-(3-methoxyphenyl)-1-phenylethylene (7), 1-(4-methoxyphenyl)-1-phenylethylene (8), 3-(3-methoxyphenyl)inde
- Arnold, Donald R.,Du, Xinyao,Henseleit, Kerstin M.
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p. 839 - 852
(2007/10/02)
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