- Nickel-Catalyzed Directed C6-Selective C-H Alkylation of 2-Pyridones with Dienes and Activated Alkenes
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A pyridine-directed, C6-selective nickel-catalyzed ring-contracting C-H alkylation of 2-pyridones with 1,5-cyclooctadiene (cod) has been developed. The reaction proceeds smoothly under external-ligand-free conditions and is accelerated uniquely by a K3PO4 base. Preliminary mechanistic investigations with deuterium-labeled substrates and related reactions with some alkenes are also disclosed.
- Miura, Wataru,Hirano, Koji,Miura, Masahiro
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- Asymmetric Markovnikov Hydroaminocarbonylation of Alkenes Enabled by Palladium-Monodentate Phosphoramidite Catalysis
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A palladium-catalyzed asymmetric Markovnikov hydroaminocarbonylation of alkenes with anilines has been developed for the atom-economical synthesis of 2-substituted propanamides bearing an α-stereocenter. A novel phosphoramidite ligand L16 was discovered which exhibited very high reactivity and selectivity in the reaction. This asymmetric Markovnikov hydroaminocarbonylation employs readily available starting materials and tolerates a wide range of functional groups, thus providing a facile and straightforward method for the regio- and enantioselective synthesis of 2-substituted propanamides under ambient conditions. Mechanistic studies revealed that the reaction proceeds through a palladium hydride pathway.
- Yao, Ya-Hong,Yang, Hui-Yi,Chen, Ming,Wu, Fei,Xu, Xing-Xing,Guan, Zheng-Hui
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supporting information
p. 85 - 91
(2021/01/12)
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- Polymerization of Allenes by Using an Iron(II) β-Diketiminate Pre-Catalyst to Generate High Mn Polymers
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Herein, we report an iron(II)-catalyzed polymerization of arylallenes. This reaction proceeds rapidly at room temperature in the presence of a hydride co-catalyst to generate polymers of weight up to Mn=189 000 Da. We have determined the polymer structure and chain length for a range of monomers through a combination of NMR, differential scanning calorimetry (DSC) and gel permeation chromatography (GPC) analysis. Mechanistically, we postulate that the co-catalyst does not react to form an iron(II) hydride in situ, but instead the chain growth is proceeding via a reactive Fe(III) species. We have also performed kinetic and isotopic experiments to further our understanding. The formation of a highly unusual 1,3-substituted cyclobutane side-product is also investigated.
- Durand, Derek J.,Webster, Ruth L.,Woof, Callum R.
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supporting information
p. 12335 - 12340
(2021/07/19)
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- The Catalytic Asymmetric Intermolecular Prins Reaction
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Despite their significant potential, catalytic asymmetric reactions of olefins with formaldehyde are rare and metal-free approaches have not been previously disclosed. Here we describe an enantioselective intermolecular Prins reaction of styrenes and paraformaldehyde to form 1,3-dioxanes, using confined imino-imidodiphosphate (iIDP) Br?nsted acid catalysts. Isotope labeling experiments and computations suggest a concerted, highly asynchronous addition of an acid-activated formaldehyde oligomer to the olefin. The enantioenriched 1,3-dioxanes can be transformed into the corresponding optically active 1,3-diols, which are valuable synthetic building blocks.
- Diáz-Oviedo, C. David,Maji, Rajat,List, Benjamin
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supporting information
p. 20598 - 20604
(2021/12/14)
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- Phosphonium Phenolate Zwitterion vs Phosphonium Ylide: Synthesis, Characterization and Reactivity Study of a Trimethylphosphonium Phenolate Zwitterion
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4-Methoxy-3-(trimethylphosphonio)phenolate was obtained from a regioselective addition of PMe3 to p-quinone monoacetal. This compound undergoes hydrogen isotope exchange with D2O or CD3CN, and is capable of catalyzing H/D exchange of CD3CN with substrates bearing weakly acidic hydrogens. It exhibits similar reactivity to phosphorus ylides for olefinations of aldehydes. A possible tautomerization between the phosphonium phenolate zwitterion and phosphonium ylide is proposed for the first time to rationalize the unique reactivity.
- Xiao, Jing,Li, Qiang,Shen, Ruwei,Shimada, Shigeru,Han, Li-Biao
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supporting information
p. 5715 - 5720
(2019/11/22)
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- Copper-catalyzed dehydrogenative borylation of terminal alkynes with pinacolborane
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LCuOTf complexes [L = cyclic (alkyl)(amino)carbenes (CAACs) or N-heterocyclic carbenes (NHCs)] selectively promote the dehydrogenative borylation of C(sp)-H bonds at room temperature. It is shown that σ,π-bis(copper) acetylide and copper hydride complexes are the key catalytic species.
- Romero, Erik A.,Jazzar, Rodolphe,Bertrand, Guy
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p. 165 - 168
(2016/12/30)
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- Mechanistic insights into catalytic linear cross-dimerization between conjugated dienes and styrenes by a ruthenium(0) complex
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The mechanistic studies for linear cross-dimerization between 2,3-dimethylbuta-1,3-diene and styrene by a Ru(0) complex, Ru(η6-naphthalene)(η4-1,5-COD) (1), are performed both by kinetic and computational studies. This reaction is ba
- Hirano, Masafumi,Ueda, Takao,Komine, Nobuyuki,Komiya, Sanshiro,Nakamura, Saki,Deguchi, Hikaru,Kawauchi, Susumu
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p. 174 - 184
(2015/09/22)
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- Taming living carbocations in catalytic direct conjugate addition of simple alkenes to α,Enones
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A Lewis acid in the presence of an anionic phosphate ligand enables the addition of alkenes to α,enones. The ligand facilitates selective proton elimination by suppressing competing pathways, thus leading to vinylation adducts in high yields (up to 99%) for a broad range of substrates.
- Lv, Jian,Zhong, Xingren,Luo, Sanzhong
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supporting information
p. 8293 - 8296
(2014/07/08)
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- Hydride-rhodium(III)-N-heterocyclic carbene catalysts for vinyl-selective h/d exchange: A structure-activity study
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A series of neutral and cationic RhIII-hydride and Rh III-ethyl complexes bearing a NHC ligand has been synthesized and evaluated as catalyst precursors for H/D exchange of styrene using CD 3OD as a deuterium source. Various ligands have been examined in order to understand how the stereoelectronic properties can modulate the catalytic activity. Most of these complexes proved to be very active and selective in the vinylic H/D exchange, without deuteration at the aromatic positions, displaying very high selectivity toward the positions. In particular, the cationic complex [RhClH(CH3CN)3(IPr)]CF 3SO3 showed excellent catalytic activity, reaching the maximum attainable degree of vinylic deuteration in only 20 min. By modulation of the catalyst structure, we obtained improved α/β selectivity. Thus, the catalyst [RhClH(κ2-O,N-C9H 6NO)(SIPr)], bearing an 8-quinolinolate ligand and a bulky and strongly electron-donating SIPr as the NHC, showed total selectivity for the β-vinylic positions. This systematic study has shown that increased electron density and steric demand at the metal center can improve both the catalytic activity and selectivity. Complexes bearing ligands with very high steric hindrance, however, proved to be inactive.
- Di Giuseppe, Andrea,Castarlenas, Ricardo,Perez-Torrente, Jesus J.,Lahoz, Fernando J.,Oro, Luis A.
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p. 8391 - 8403
(2014/07/08)
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- Oxidative cleavage and rearrangement of aryl epoxides using iodosylbenzene: On criegee's trail
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Aryl epoxides undergo rearrangement and oxidative cleavage when reacted with in situ prepared hydroxy-λ3-iodane complexes. The presence of H2O plays a decisive role in steering the reaction path. A mechanistic scheme is proposed that accounts for the observed chemoselectivities. Copyright
- Havare, Nizam,Plattner, Dietmar A.
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p. 2036 - 2042
(2013/01/15)
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- Mild and selective H/D exchange at the β position of aromatic α-olefins by N-heterocyclic carbene-hydride-rhodium catalysts
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Pacman bites selectively! Stable rhodium(III)-N-heterocyclic carbene-hydride complexes (Pacman-like catalysts) are highly active and selective catalysts for H/D exchange at the β position of aromatic α-olefins (see picture). The interplay between bulky N-
- Di Giuseppe, Andrea,Castarlenas, Ricardo,Perez-Torrente, Jesus J.,Lahoz, Fernando J.,Polo, Victor,Oro, Luis A.
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supporting information; experimental part
p. 3938 - 3942
(2011/06/24)
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- On the isolation of neat allylic fluorides
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Neat cinnamyl fluoride, geranyl fluoride, 5-carbomethoxy-3-fluorocyclohexene and parent 3-fluorocyclohexene undergo spontaneous decomposition on contact with borosilicate glass or catalytic quantities of moderately strong acids that consists in polycondensation with elimination of HF initiated by electrophilic abstraction of F-. Acid sensitivity of these allylic fluorides correlates with stability of respective allylic cations, exceeds that of parent benzyl fluoride, yet can be mitigated by the use of Teflon and PFA containers that permit their isolation and handling in the neat state.
- Lee, Eunsung,Yandulov, Dmitry V.
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scheme or table
p. 474 - 483
(2009/12/06)
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- Ruthenium dihydrogen complex for C-H activation: Catalytic H/D exchange under mild conditions
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Catalytic H/D-exchange reactions were studied with [Ru(dtbpmp) (η2-H2)(H)2] (1) as catalyst. Under mild reaction conditions (25-75°C) a wide range of arenes and olefins undergo H/D exchange with [D6]benzene. A p
- Prechtl, Martin H. G.,Hoelscher, Markus,Ben-David, Yehoshoa,Theyssen, Nils,Milstein, David,Leitner, Walter
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experimental part
p. 3493 - 3500
(2009/02/07)
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- Efficient syntheses of four stable-isotope labeled (1R)-menthyl (1S,2S)-(+)-2-phenylcyclopropanecarboxylates
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Many carbenoid cyclopropanation reactions promoted by chiral catalysts give product mixtures reflecting impressive diastereo- and enantioselectivities. Few provide a single chiral product efficiently. This limitation has been overcome in cyclopropanations of styrene and isotopically labeled styrenes with α-diazoacetates. Convenient syntheses on a 20 g scale of each of four chiral isotopically labeled (1R)-menthyl (1S,2S)-2- phenylcyclopropanecarboxylates (the 1-d-3-13C, 1,(3S)-d2, 1,2,(3S)-d3, and 1,3,3-d3 isotopomers) of better than 99% ee have been realized. The Royal Society of Chemistry 2006.
- Keliher, Edmund J.,Burrell, Richard C.,Chobanian, Harry R.,Conkrite, Karina L.,Shukla, Rajesh,Baldwin, John E.
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p. 2777 - 2784
(2008/09/16)
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- On the mechanism of the copper-catalyzed cyclopropanation reaction
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The selectivity-determining step in enantioselective copper-catalyzed cyclopropanation with diazo compounds has been studied by experimental and computational methods. The addition of the very reactive metallacarbene intermediate in an early transition st
- Rasmussen, Torben,Jensen, Jakob F.,stergaard, Niels,Tanner, David,Ziegler, Tom,Norrby, Per-Ola
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p. 177 - 184
(2007/10/03)
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- Rhodium- and palladium-catalysed proton exchange in styrene detected in situ by para-hydrogen induced polarization
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In situ NMR spectroscopy of para-hydrogen induced nuclear polarization shows a pairwise proton exchange mechanism in styrene during homogeneous hydrogenation with rhodium(I) and palladium(0) catalysts.
- Harthun, Andreas,Giernoth, Ralf,Elsevier, Cornelis J.,Bargon, Joachim
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p. 2483 - 2484
(2007/10/03)
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- On the Thermal Cycloisomerization of 1-Vinylnaphthalene to Acenaphthene. A Mechanistic D-Labeling Study
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Unlabeled 1-vinylnaphthalene (1) as well as positionally D-labeled 1 have been prepared and subjected to gas phase pyrolysis at low partial pressures of the educt compounds in nitrogen.At 700 deg C, 1 rearranges exclusively to acenaphthene (2).Under the conditions applied a significant H-D-exchange in the 1-vinylnaphthalene as well as in the formed acenaphthene takes place.The results obtained in this way and those resulting from pyrolysis in hydrogen (instead of nitrogen) show that despite the very high degree of dilution the high selectivity of cycloisomerization from 1 to 2 is firstly controlled by H-atom driven radical chain processes, in which the cyclization of the 2-naphthylethylradical dominates the reaction course.
- Zimmermann, Gerhard,Ondruschka, Bernd,Nuechter, Matthias,Kopinke, Frank-Dieter,Remmler, Matthias
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p. 415 - 420
(2007/10/02)
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- Quinolinium Dichromate Oxidations. Kinetics and Mechanism of the Oxidative Cleavage of Styrenes
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The kinetics of oxidation of styrene and substituted styrenes by quinolinium dichromate (QDC) in dimethyl formamide, in the presence of acid, has been investigated.The rate of the reaction is dependent on the first powers of the concentrations of substrate, oxidant, and acid.A small inverse kinetic isotope effect has been observed (kH/kD = 0.80).Correlation with ? yielded a ρ value of -4.0, suggesting the formation of a cationic intermediate in the rate-determining step of the reaction.Subsequent cleavage of the carbon-carbon bond yielded benzaldehyde and formaldehyde.
- Nongkynrih, Irona,Mahanti, Mahendra K.
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p. 4925 - 4928
(2007/10/02)
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- The effect of the nature of the amine leaving group on the nature of the E2 transition state for the reaction of 1-phenylethylammonium ions with sodium ethoxide in ethanol
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To investigate the effect of the leaving group on the elimination reaction of 1-phenylethylammonium ions with sodium ethoxide in ethanol at 60 deg C, the reaction of seven different quaternary ammonium salts and their β-deuterated analogues with trimethylamine, N-methylpiperidine, N-methyldiethylamine, triethylamine, N,N-dimethylbenzylamine, tripropylamine, and N,N-diethylbenzylamine as leaving groups has been studied.In all cases the elimination, which was shown to proceed via the concerted E2 process, was accompained by competing substitution reactions.Although a significant depedence of the rate of the elimination process on the nature of the leaving group was noted, there was not any linear correlation with the basicity of the amine leaving group.The primary hydrogen-deuterium kinetic isotope effect for the elimination process, (kH/kD)E, was found to increase initially with an increase of reaction rate, kHE, for substrates containing the leaving groups trimethylamine, N-methylpiperidine, N-methyldiethylamine, triethylamine, and N,N-dimethylbenzylamine; i.e., (kH/kD)E=5.03, 5.26, 5.40, 5.83, and 5.85, respectively.A further increase in rate, using substrates with tripropylamine and N,N-diethylbenzylamine as leaving groups resulted in a decrease of the magnitude of the hydrogen-deuterium isotope effect; i.e., (kH/kD)E= 5.42 and 4.67, respectively.It is concluded that steric effects mainly determine leaving group ability.As well, it is concluded that the leaving group ability of the amine determines the structure of the E2 transition state.For the reaction of the poorer leaving groups, trimethylamine, N-methylpiperidine, and N-methyldiethylamine, the proton is more than one-half transferred at the transition state while for reaction involving the two best leaving groups, tripropylamine and N,N-diethylbenzylamine, the Cβ-H bond is less than one-half broken at the transition state.The conclusions are considered in the light of the More O'Ferrall-Jencks potential energy surface diagram.Key words: elimination mechanism, transition state, isotope effects, leaving group, quaternary salts.
- Smith, Peter James,Amin, Md.
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p. 1457 - 1467
(2007/10/02)
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- Gas-Phase Pyrolysis of Phenylcyclopropane
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The gas-phase pyrolysis of phenylcyclopropane (5) has been ivestigated in a quartz tubular reactor between 560 and 680 deg C and a contact time of about 1 s.Main reaction is the thermal isomerization to allylbenzene (4) as well as to cis-(1b) and trans--β-methylstyrene (3b).Besides 1, 3, and 4, indene (8) is formed, which is characterized by a statistical distribution of the H atom over the three positions of the five-membered ring.To distinguish between the two possible mechanisms of the isomerization (opening of the cyclopropane ring C-C bond dissociation/ 1,3-diyl formation and 1,2-C,H retro-insertion/ethylcarbene formation), the D distribution in 1 and 3 was carefully determined by 1H-NMR spectroscopy.The results show that the isomerization is initiated by generation of a 1,3-diradical. - Keywords: Isotopic labeling/ Isomerization/ Phenylcyclopropane/ Pyrolysis
- Kopinke, Frank-Dieter,Zimmermann, Gerhard,Aust, Janette,Scherzer, Klaus
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p. 721 - 726
(2007/10/02)
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- Rhodium catalyzed deuteroformylation of styrene: (E)- and (Z)-β-deuterostyrene and Β, β-dideuterostyrene formation via selective β-hydride elimination from the branched alkylrhodium intermediate
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Deuteroformylation of styrene in the presence of Rh4(CO)12 as a catalytic precursor was carried out at 160 atm of CO and D2 1/1 at two temperatures (20 and 90 deg C) and for times yielding partial or complete conversion.Compounds recovered from the mixture produced by reaction and partial conversion at 90 deg C include unlabeled styrene, (E)- and (Z)-β-deuterostyrene, C6H5CH=CHD, and β,β-dideuterostyrene, C6H5CH=CD2, whereas at room temperature the styrene does not take up deuterium.These results indicate that under hydroformylation conditions the branched alkylrhodium intermediate, which affords the branched aldehyde, in part dissociates into rhodium hydride and deuterated olefin.By contrast the linear alkyl intermediate does not disssociate under the same conditions, but instead yields almost completely the corresponding aldehyde.
- Lazzaroni, Raffaello,Settambolo, Roberta,Raffaelli, Andrea,Pucci, Sergio,Vitulli, Giovanni
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p. 357 - 366
(2007/10/02)
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- CIDNP Evidence for a 'Hot' Carbocation formed by Electron Transfer between Two Radicals
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The radical pair (2), containing 2-phenylethyl and m-chlorobenzoyloxy radicals, produced from β-phenylpropionyl m-chlorobenzoyl peroxide (1), gives rearraged products; the observations of CIDNP and product analyses suggest that the 2-phenylethyl carbocation initially produced by electron transfer within the radical pair is a 'hot' carbocation which retains the ground state configuration of its neutral radical precursor.
- Lee, Sueg-Geun
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p. 1115 - 1117
(2007/10/02)
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- Preparation of deuterium labelled styrenes and divinylbenzenes
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Specifically deuteriated styrenes (1-d, 2,2'-d2, and ring labelled), perdeuteriostyrene, and specifically deuteriated divinylbenzenes (1,1'-d2 2,2,2',2'-d4, and ring labelled) have been prepared by transforming suitably labelled phenylacetic (hydride or d
- Werstiuk, Nick Henry,Timmins, George
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p. 1072 - 1076
(2007/10/02)
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- THE MECHANISM OF REACTIONS OF ORGANOPALLADIUM SALTS WITH VINYLCYCLOPROPANES
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Cyclopropylmercuric chloride, lithium chloropalladite and methyl acrylate react at 0-25 deg C to give an 81percent yield of methyl sorbate.A ?-allylic palladium intermediate is proposed since vinylcyclopropane, carbomethoxymercuric acetate, and lithium chloropalladate give the same product.The corresponding reactions with styrene and cyclopropylmercuric chloride or vinylcyclopropane and phenylmercuric chloride also give the same, isolable ?-allylic palladium complex.Deuterium labeling experiments support the occurrence of a common intermediate in the two reactions. 1,1-Dicarboethoxy-2-vinylcyclopropane reacts similarly with "phenylpalladium chloride" but the ?-allylic product has the palladium attached at the benzyl carbon rather than the next carbon away.The reaction with "phenylpalladium acetate" in place of the chloride yields only dienes.Studies with the deuterated vinylcyclopropane diester suggest that the mode of elimination from the initial palladium adduct is strongly influenced by the anion present.The reaction of "cyclopropylpalladium chloride" with alkenes appears to be a general method for preparing, selectively, internal ?-allylic palladium complexes.
- Fischetti, William,Heck, Richard F.
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p. 391 - 405
(2007/10/02)
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