- Stereo and regioselectivity in the phenylation of cationic allylpalladium(II) α-diimine complexes by tetraphenylborate anion
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The reaction of the cationic complex 3-cyclohexenyl>(py-2-CH=NC6H4OMe-4)>+ (1) with BPh4- in the presence of fumaronitrile yields trans-3-methoxy-6-phenylcyclohexene (2a) and trans-4-methoxy-3-phenyl-cycohexene (2b), in ca. 1:1 molar ratio.The trans stereochemistry of these products implies that the phenylation of the allyl ligand involves prior transfer of a phenyl group from BPh4- to the metal, followed by reductive coupling of the organic moieties.In the reaction of 3-1,1-R1,R2-C3H3)(N-N')>+ (3) 1 = H, R2 = Ph, Me; R1 = R2 = Me> with BPh4- in the presence of activated olefins, both regioisomers PhCH2-CH=CR1R2 (4a) and CH2=CH-CR1R2Ph (4b) are formed with a relative ratio which depends essentially on the allylic substituents: R1 = H, R2 = Ph, 4a above 98percent; R1 = H, R2 = Me, 4a 75-67percent; R1 = R2 = Me, 4a 64-58percent.The regioisomer distribution is very little affected by the nature of the α-diimine, of the activated olefin, and of the solvent.For R1 = H and R2 = Ph, Me, the olefinic product 4a has a trans (E) geometry.These results have been interpreted in terms of reductive elimination occurring in the intermediate 3-1,1,R1,R2C3H3)(N-N')> with a ?-N monodentate α-diimine ligand.
- Crociani, Bruno,Antonaroli, Simonetta,Bianca, Francesca Di,Fontana, Alberta
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- Syntheses of Molybdenum(VI) Imido Alkylidene Complexes That Contain a Bidentate Dithiolate Ligand
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Zn(DCTC) (DCTC = 3,6-dichlorodithiacatecholate) reacts with Mo(NAd)(CHCMe2Ph)Cl2(PPh2Me) (Ad = 1-adamantyl) to give Mo(NAd)(CHCMe2Ph)(DCTC)(PPh2Me). The reactions between Zn(DCTC) and Mo(NAd)(CH-t-Bu)(OTf)2(dme) or Mo(NAr)(CHCMe2Ph)(OTf)2(dme) (Ar = 2,6-i-Pr2C6H3; OTf = triflate; dme = 1,2-dimethoxyethane) produce [Mo(NAd)(CH-t-Bu)(DCTC)]2 and [Mo(NAr)(CHCMe2Ph)(DCTC)]2, respectively. Complexes that contain a 3,3′,5,5′-tetrasubstituted dithiabiphenolate were prepared in a reaction between Mo(NAr)(CHCMe2Ph)(Me2pyr)2 (Me2pyr = 2,5-dimethylpyrrolide) and the 3,3′,5,5′-tetrasubstituted dithiabiphenols, (3,3′,5,5′-tetrachlorodithiabiphenol (H2Cl4S2), 3,3′,5,5′-tetrabromodithiabiphenol (H2Br4S2), and 3,3′,5,5′-tetra-t-Bu-dithiabiphenol (H2Bu4S2)). The isolated complexes include Mo(NAr)(CHCMe2Ph)(Cl4S2)(pyridine), Mo(NAr)(CHCMe2Ph)(Br4S2)(pyridine), Mo(NAr)(CHCMe2Ph)(Bu4S2)(PMe3), and [Mo(NAr)(CHCMe2Ph)(Cl4S2)]2. Only the dithiabiphenolate derivatives (in the presence of B(C6F5)3) show activity for the metathesis of 1-decene, and although that reaction is limited by a sensitivity of the alkylidene complexes to ethylene, as suggested by the reaction between ethylene and Mo(NAr)(CHCMe2Ph)(Bu4S2) to give the ethylene complex, Mo(NAr)(C2H4)(Bu4S2). Mo(NAr)(C2H4)(Bu4S2) was unstable with respect to loss of ethylene and formation of an ethylene-free dimer. Mo(NAd)(CHCMe2Ph)(DCTC)(PPh2Me), [Mo(NAr)(CHCMe2Ph)(DCTC)]2, and [Mo(NAr)(CHCMe2Ph)(Cl4S2)]2 were characterized crystallographically.
- Tafazolian, Hosein,Tsay, Charlene,Schrock, Richard R.,Müller, Peter
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- Mode attack of atomic carbon on benzene rings
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Reaction of are generated carbon atoms with tert-butylbenzene, 4, gives 3-methyl-3-phenyl-1-butene, 5, and 1,1-dimethylindane, 6. Labeling studies and isotope effects demonstrate that 5 results from an insertion into a methyl C-H bond followed by 1,2 hydrogen shift while 6 arises from initial ortho C-H insertion followed by intramolecular insertion into a methyl C-H bend. When fluoroboric acid is added to the 77 K matrix of 4 + C, tert-butyltropylium fluoroborate, 18, is formed. Labeling studies indicate that 18 results from initial insertion of C into meta and para C-H bonds of 4 followed by ring expansion to cycloheptatetraenes which are subsequently protonated. The reaction of C with benzene gives similar results, indicating that initial C-H insertion is the preferred mode of attack of atomic carbon on benzene rings.
- Armstrong, Brian M.
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- Reactivity of mixed organozinc and mixed organocopper reagents: 14. Phosphine-nickel catalyzed aryl-allyl coupling of (n-butyl)(aryl)zincs. Ligand and substrate control on the group selectivity and regioselectivity
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The group selectivity and regioselectivity in the allylation of mixed (n-butyl)(aryl)zinc reagents in THF depends on the nickel catalyst type and also on nature of the allylic substrate. Allylation of (n-butyl)(phenyl)zinc reagent with alkyl substituted primary allylic chlorides and acetates in the presence of NiCl2(dppf) catalysis affords the phenyl coupling product with γ-selectivity. However, allylation with aryl substituted primary allylic substrates results in both phenyl- and alkyl-coupling products with medium α-selectivity in the presence of NiCl2(dppf) catalysis whereas phenyl coupling product is formed with α-selectivity in the presence of NiCl2(Ph3P)2 catalysis. This new NiCl2(dppf) catalyzed protocol for γ-selective aryl allylation of (n-butyl)(aryl)zinc reagents with alkyl substituted primary allylic chlorides in THF at room temperature provides an atom economic alternative to allylation of (aryl)2Zn reagents. A mechanism for the dependence of group selectivity and regioselectivity of Ni catalyzed allylation of (n-butyl)(aryl)zinc reagents on the catalyst ligand and the substrate was proposed.
- Kalkan, Melike,Erdik, Ender
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- Short synthesis of chiral 4-substituted (S)-imidazolinium salts bearing sulfonates and their use in γ-selective reactions of allylic halides with grignard reagents
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A one-pot reaction of Boc-protected amino alcohols and 2-sulfobenzoic anhydride followed by the addition of a wide variety of primary amines has allowed rapid access to diverse libraries of amidosulfonates 1,2-C 6H4(SO3su
- Latham, Christopher M.,Blake, Alexander J.,Lewis, William,Lawrence, Matthew,Woodward, Simon
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supporting information; experimental part
p. 699 - 707
(2012/03/11)
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- Catalyst-free suzuki-type coupling of allylic bromides with arylboronic acids
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The coupling of arylboronic acids with electron-rich allylic bromides is accomplished in the absence of any transition-metal catalyst through conventional heating. The reaction is completely regioselective, affording only the α-coupled product, and can be carried out under mild aerobic conditions in an organic solvent; the presence of a base is required. Copyright
- Scrivanti, Alberto,Beghetto, Valentina,Bertoldini, Matteo,Matteoli, Ugo
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supporting information; experimental part
p. 264 - 268
(2012/02/04)
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- Understanding the effect of allylic methyls in olefin cross-metathesis
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A series of NMR spectroscopy experiments have been conducted with both the model compound, 3-methyl-1-pentene and the corresponding ADMET monomer 3,6,9-trimethylundeca-1,10-diene (11) to better understand the effect of allylic methyls during olefin metath
- Courchay, Florence C.,Baughman, Travis W.,Wagener, Kenneth B.
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p. 585 - 594
(2007/10/03)
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- Zirconium-mediated conversion of homoallylic ethers into cyclopropane derivatives
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Homoallylic ethers react with Cp2ZrCl2/2 n-BuLi reagent to afford cyclopropane derivatives. Cyclopropylcarbinyl-homoallyl rearrangements involving zirconium species are observed depending on the substrate structure.
- Gandon, Vincent,Laroche, Christophe,Szymoniak, Jan
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p. 4827 - 4829
(2007/10/03)
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- Heterodimerization of Olefins. 1. Hydrovinylation Reactions of Olefins That Are Amenable to Asymmetric Catalysis
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Through a systematic examination of ligand and counterion effects, new protocols for a nearly quantitative and highly selective codimerization of ethylene and various functionalized vinylarenes have been discovered. In a typical reaction, 4-bromostyrene and ethylene undergo codimerization in the presence of 0.0035 equiv each of [(allyl)NiBr]2, triphenylphosphine, and AgOTf in CH2Cl2 at -56 °C to give 3-(4-bromophenyl) -1-butene in >98% yield and selectivity. Corresponding reactions with [(allyl)PdX]2 are much less efficient and less selective and may require further optimization before a viable system can be identified. Another useful protocol that gives comparable yield and selectivity involves the use of a single-component catalyst prepared from allyl 2-diphenylphosphinobenzoate, Ni(COD)2, and (C6F5)3B. Recognition of a synergistic relationship between a chiral hemilabile ligand (for example, (R)-2-methoxy-2′-diphenylphosphino-1,1′-binaphthyl, MOP) and a highly dissociated counteranion (BARF or SbF6) in an enantioselective version of the Ni-catalyzed reaction raises the prospects of developing a practical route for the synthesis of 3-arylbutenes. Several pharmaceutically relevant compounds, including widely used 2-arylpropionic acids, can be synthesized from these key intermediates. This reaction appears to be quite general. Synthesis of several new 2-diphenylphosphino-1,1-binaphthyl derivatives, prepared to probe the effect of hemilabile coordination on the efficiency and selectivity of the reaction, are also described.
- RajanBabu,Nomura, Nobuyoshi,Jin, Jian,Nandi, Malay,Park, Haengsoon,Sun, Xiufeng
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p. 8431 - 8446
(2007/10/03)
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- Nickel catalyzed hydrovinylation of arylethylenes: General method of synthesis of α-arylpropionic acids intermediates
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The hydrovinylation of arylethylenes catalyzed by [Ni(MeCN)6][BF4]2/AlEt2Cl/PPh3 was modulated to obtain 3-aryl-1-butenes in high yields and selectivities. A wide variety of arylethylenes containing electron-donating or electron-withdrawing groups and Lewis basic group, can be hydrovinylated at room temperature and under mild conditions by changing the relative ratios of the three-component catalyst. Similar activities and selectivities were observed for o-, m- and p-substituted styrenes. Also, the hydrovinylation of olefins with substituents in the vinyl fragment, such as α-methylstyrene and indene, can be accomplished. (C) 2000 Elsevier Science Ltd.
- Fassina, Viviane,Ramminger, Carolina,Seferin, Marcus,Monteiro, Adriano L
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p. 7403 - 7409
(2007/10/03)
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- Synthesis of 3-aryl-1-butenes by the nickel catalyzed hydrovinylation of styrene derivatives
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The synthesis of 3-aryl-1-butenes is performed by hydrovinylation of styrene and alkyl-substituted styrenes catalyzed by [Ni(MeCN)6][BF4]2/Et2AlCl/PPh3 under mild conditions with very good activities
- Monteiro, Adriano Lisboa,Seferin, Marcus,Dupont, Jairton,De Souza, Roberto Fernando
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p. 1157 - 1160
(2007/10/03)
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- Carbonium Ion Rearrangements Controlled by the Presence of a Silyl Group
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γ-Silyl tertiary alcohols rearrange in protic acid with 1,2-shift of hydride, phenyl, or alkyl groups, and loss of the silyl group to give alkenes.The placing of the silyl group thus controls the carbonium ion rearrangement in a preparatively useful way.Methoxycarbonyl groups do not migrate; instead, cyclopropanes are formed, except when the conformation suitable for cyclopropane formation is unattainable.When the alkene product is 2,2-disubstituted, it can be reprotonated under the reaction conditions and does not therefore always survive.This can be avoided by carrying out the reaction using a Lewis acid on the silyl ether.The starting γ-silyl alcohols are prepared by a variety of versatile methods.
- Fleming, Ian,Patel, Shailesh K.,Urch, Christopher J.
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p. 115 - 124
(2007/10/02)
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- Photochemical reactivity of α-phenyl β,γ-enones. Singlet 1,3-acyl shift, triplet aromatic di-?-methane (DPM) rearrangement and triplet aryl-carbonyl bridging
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The photochemistry of the series of α-phenyl β,γ-enones 6-10 has been studied under conditions of both direct (λ 300 nm) and triplet-sensitized irradiation with the aim of determining the reactivity patterns of these "multi"-chromophoric systems.Upon direct irradiation, the reactants exhibit the typical photoreactions of β,γ-enones, viz. the 1,3-acyl shift, affording the corresponding (E)- and (Z)-5-phenyl-4-hexen-3-ones, decarbonylation of the radicals formed by α-cleavage and recombination of the resulting alkyl radicals and, in addition, a new type of reaction from the triplet-excited state yielding small amounts of the corresponding acetophenones.The acetophenones are thought to be formed by initial β-bridging between the carbonyl and the phenyl group, followed by extrusion of the C4H6 fragment from the 1,4- or 1,3-oxa-diradical.Upon sensitized irradiation, the o-methoxy- and p-cyano-substituted reactants 9 and 10 exhibit the di-?-methane rearrangement, leading to mixtures of the corresponding cis- and trans-1-acetyl-1-methyl-2-phenylcyclopropanes, with quantum yields of 0.03 and 0.10, respectively.The formation of the 1,3-AS and decarbonylation products illustrates the occurrence of α-cleavage, whereas the acetophenones and di-?-methane products are formed via initial aryl-carbonyl and aryl-vinyl bridging, respectively.The inability of the other α-phenyl β,γ-enones to undergo photocyclopropanation is discussed in terms of excitation-energy partition.In the o-methoxy and p-cyano-substituted reactants, the excitation energy may be predominantly concentrated in the aryl moiety in contrast to the other two systems in which the excitation energy may be mainly localized on the β,γ-enone moiety.Subsequent triplet-energy dissipation by a free-rotor mechanism would then account for the stability of these systems.This was observed for (E)-7 which, upon triplet sensitization, affords only the (Z) isomer, whereas this process is degenerate for the other substrates studied.
- Koppes, Margareth J. C. M.,Beentjes, Peter C. J.,Cerfontain, Hans
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p. 313 - 324
(2007/10/02)
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- The Aryl Version of the Cyclopropyl-?-Methane Rearrangement. Partitioning of a 1,4-Diradical: Mechanistic and Exploratory Organic Photochemistry
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The photochemistry of 2-(2,2-diphenylcyclopropyl)-2-phenylpropane (8) was investigated in a search for the arylcyclopropylmethane counterpart of the known vinylcyclopropylmethane reaction.Direct irradiation of arylcyclopropylmethane 8 led to 1,1-diphenylethylene (3) and 1-phenyl-2-methyl-1-propene (13) as products in addition to the usual Griffin fragmentation leading to diphenylcarbene (15) and 3-methyl-3-phenyl-1-butene (7). 1,1,3-Triphenyl-2,2-dimethylcyclobutane (12) was considered as a potential reaction intermediate.The cyclobutane was synthesized and found to afford alkenes 3 and 13 on irradiation.However, dynamic isotope dilution revealed that only 1percent of the reaction did proceed via this intermediate, and its presence was eventually detected by FT NMR.The triplet of arylcyclopropane 8 proved unreactive.A third mechanism involving a Griffin fragmentation was considered and ruled out by independent generation of the carbene and observation of the products.Quantum yields were obtained.Also excited singlet-state lifetimes and reaction rates were determined by using single photon counting.The electronic features leading to the observed reactivities are discussed.
- Zimmerman, Howard E.,Carpenter, Clint W.
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p. 3298 - 3305
(2007/10/02)
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- Metallacarboranes in Catalysis. 6. Kinetics and Mechanism of Alkene Hydrogenation and Isomerization Catalyzed by Rhodacarborane Clusters. A Search for Cluster Catalysis
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In a search for cluster-catalyzed reactions the rhodacarboranes (1), (II), (III), and (IV) were employed as catalyst precursors in a study of 1-hexene (B) isomerization.Precursors I, III, and IV were examined in the hydrogenation of 3-methyl-3-phenyl-1-butene (A).Complete rate laws were developed for isomerization and hydrogenation.Studies with D2 demonstrated the presence of reversible alkylrhodium formation during hydrogenation.The use of D-labeled catalyst precursors, etc., proved that the Rh-H ligand of the closo precursors was not directly involved in either alkene isomerization or in hydrogenation.Competitive isomerization and hydrogenation of 1-hexene catalyzed by precursors I and IV suggested the presence of a common intermediate for these two reactions.Extensive intermolecular D scrambling was observed in equilibration experiments which employed propene-1,1,1-d3 and propene-2-d with precursor I and isotopically normal propene.The slow regiospecific transfer of deuterium from carbon in A to the 9, 10, and 12 boron vertices in I was observed and is believed to proceed via H-Rh-B bonded intermediates.The mechanistic implications of these and other observations are integrated into a mechanistic scheme which is based upon the prior equilibrium of Rh(3+) closo- and Rh(1+) exo-nido-rhodacarboranes which, in the presence of alkene, produce an equilibrium concentration of a key (phosphine)(alkene)Rh(1+) exo-nido intermediate regardless of the closo or exo-nido nature of the catalyst precursor used.Alkene isomerization is thought to involve η3-allylic intermediates produced from the exo-nido alkene complex.Hydrogenation appears to proceed via oxidative addition of H2 to this same complex followed by rate-determining decomposition of the hydridorhodium alkyl produced by this means.These kinetic characteristics may have their origin in the weak electron-donor properties of the chelated exo-nido-C2B9H12(1-) ligands which are attached to Rh(1+) or Rh(3+) in the exo-nido intermediates by a pair of B-H-Rh three-center, two-electron bonds.
- Behnken, Paul E.,Belmont, James A.,Busby, David C.,Delaney, Mark S.,King, Roswell E.,et al.
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p. 3011 - 3025
(2007/10/02)
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- A HYBRID BIRCH-CLAISEN METHODOLOGY FOR ARYLATION AT ALLYLIC TERMINI: SYNTHESIS OF (+/-)-HERBERTENE
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A hybrid Birch-Claisen methodology has been developed for the regio- and stereo-controlled arylation of allyl groups, and applied to a synthesis of (+/-)-herbertene.
- Chandrasekaran, S.,Turner, John V.
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p. 3799 - 3802
(2007/10/02)
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- Some uses of silicon compounds in organic synthesis
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1.The amount of γ-phenylthioalkylation of silyl dienol ethers is increased when the triphenylsilyl ether is used in place of the trimethylsilyl ether.Phenylthiomethylation is the least γ-selective carbon electrophile of several tried so far. 2.The acid-catalysed reactions of a range of γ-silyl tertiary alcohols cleanly give rearrangement, in which the silyl group controls the outcome.The reactions are similar in several respects to the rearrangements of the corresponding pinacols, except that the silicon controlled reactions are usually cleaner and give higher yields.The reaction is particularly useful for setting up quaternary carbon atoms.
- Fleming, Ian
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- CARBONIUM ION REARRANGEMENTS CONTROLLED BY THE PRESENCE OF A SILYL GROUP
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Tertiary alcohols with a γ-silyl group (3) generally undergo a simple carbonium ion rearrangement in acid giving a single alkene product (4) with loss of the silyl group.
- Fleming, Ian,Patel, Shailesh K.
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p. 2321 - 2324
(2007/10/02)
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- CROSS-COUPLING OF ALKENYL, ARYL OR ALLYLIC SELENIDES AND GRIGNARD REAGENTS CATALYZED BY NICKEL-PHOSPHINE COMPLEXES
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Alkenyl, aryl or allylic selenides smoothly couple with Grignard reagents in the presence of Ni(II)-phosphine complexes as catalysts to afford the corresponding unsaturated compounds in good yields.The reactivity order of coupling reaction with BuMgBr catalyzed by NiCl2 was found to be PhSeMe >> PhCl > PhSMe by the competitive reactions.
- Okamura, Hisashi,Miura, Morikazu,Kosugi, Kimihiko,Takei, Hisashi
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- Lewis Acid Mediated Reactions of Organocopper Reagents. A Remarkably Enhanced Regioselective γ-Attack of Allylic Halides and Direct Alkylation of Allylic Alcohols via RCu*BF3 System
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Chemical reactivities and selectivities of a new class of organocopper reagent, RCu-Lewis acid, are described.Regioselective γ-attack of allylic halides is realised irrespective of the degree of substitution at the two ends of the allylic systems, and of the structural factors (cyclic or acyclic) involved.Among the Lewis acids examined, BF3*OEt2 is the most effective with respect to the selectivity and total yield.Propargyl chloride and acetate are converted into 1,2-heptadiene by n-BuCu*BF3.Allylic alcohols react with 3 equiv of RCu*BF3 to produce the corresponding alkylation products in high yield.The stereochemistry of the reactions of RCu*BF3 is examined by using Goering's system, that is, 5-methyl-2-cyclohexenyl chloride, acetate, and alcohol.The substitution proceeds through a formal anti SN2' in the case of cis-5-methyl-2-cyclohexenyl acetate and through a formal syn SN2' in trans-5-methyl-2-cyclohexen-1-ol.On the other hand, the stereochemical integrity dissapears in the reaction of the cis-5-methyl-2-cyclohexen-1-ol and the chloride (1).It is proposed that the "ate" complex between RCu and BF3 is involved as a reactive intermediate.
- Yamamoto, Yoshinori,Yamamoto, Shinichi,Yatagai, Hidetaka,Maruyama, Kazuhiro
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p. 2318 - 2325
(2007/10/02)
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