- Catalytic Regioselective Olefin Hydroarylation(alkenylation) by Sequential Carbonickelation-Hydride Transfer
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Alkene hydrocarbofunctionalization represents one of the most important classes of chemical transformations, but related branched-selective examples with unactivated olefins are scarce. Here, we report that catalytic amounts of a dimeric Ni(I) complex and an exogenous alkoxide base promote Markovnikov-selective hydroarylation(alkenylation) of unactivated and activated olefins using organo bromides or triflates derived from widely available phenols and ketones. Products bearing aryl- and alkenyl-substituted tertiary and quaternary centers could be isolated in up to 95% yield and >99:1 regioisomeric ratios. Contrary to previous dual-catalytic methods that rely on metal-hydride atom transfer (MHAT) to the olefin prior to carbofunctionalization with a cocatalyst, our mechanistic evidence points toward a nonradical reaction pathway that begins with site-selective carbonickelation across the C═C bond followed by hydride transfer using alkoxide as the hydride source. Utility of the single-catalyst protocol is highlighted through the synthesis of medicinally relevant scaffolds.
- Liu, Chen-Fei,Luo, Xiaohua,Wang, Hongyu,Koh, Ming Joo
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supporting information
p. 9498 - 9506
(2021/07/19)
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- Electrochemically Enabled, Nickel-Catalyzed Dehydroxylative Cross-Coupling of Alcohols with Aryl Halides
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As alcohols are ubiquitous throughout chemical science, this functional group represents a highly attractive starting material for forging new C-C bonds. Here, we demonstrate that the combination of anodic preparation of the alkoxy triphenylphosphonium ion and nickel-catalyzed cathodic reductive cross-coupling provides an efficient method to construct C(sp2)-C(sp3) bonds, in which free alcohols and aryl bromides - both readily available chemicals - can be directly used as coupling partners. This nickel-catalyzed paired electrolysis reaction features a broad substrate scope bearing a wide gamut of functionalities, which was illustrated by the late-stage arylation of several structurally complex natural products and pharmaceuticals.
- Li, Zijian,Sun, Wenxuan,Wang, Xianxu,Li, Luyang,Zhang, Yong,Li, Chao
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supporting information
p. 3536 - 3543
(2021/03/08)
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- Cobalt-Catalyzed C(sp2)-C(sp3) Suzuki-Miyaura Cross Coupling
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A cobalt-catalyzed method for the C(sp2)-C(sp3) Suzuki-Miyaura cross coupling of aryl boronic esters and alkyl bromides is described. Cobalt-ligand combinations were assayed with high-throughput experimentation, and cobalt(II) sources with trans-N,N′-dimethylcyclohexane-1,2-diamine (DMCyDA, L1) produced optimal yield and selectivity. The scope of this transformation encompassed steric and electronic diversity on the aryl boronate nucleophile as well as various levels of branching and synthetically valuable functionality on the electrophile. Radical trap experiments support the formation of electrophile-derived radicals during catalysis.
- Ludwig, Jacob R.,Simmons, Eric M.,Wisniewski, Steven R.,Chirik, Paul J.
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- Cross-Coupling Reactions of Alkyl Halides with Aryl Grignard Reagents Using a Tetrachloroferrate with an Innocent Countercation
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Bis(triphenylphosphoranylidene)ammonium tetrachloroferrate, (PPN)[FeCl4] (1), was evaluated as a catalyst for cross-coupling reactions. 1 exhibits high stability toward air and moisture and is an effective catalyst for the reaction of secondary alkyl halides with aryl Grignard reagents. The PPN cation is considered as an innocent counterpart to the iron center. We have developed an easy-to-handle iron catalyst for “ligand-free” cross-coupling reactions. (Figure presented.).
- Hashimoto, Toru,Maruyama, Tsubasa,Yamaguchi, Takamichi,Matsubara, Yutaka,Yamaguchi, Yoshitaka
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supporting information
p. 4232 - 4236
(2019/08/16)
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- Base-catalysed reductive relay hydroboration of allylic alcohols with pinacolborane to form alkylboronic esters
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An unprecedented base-catalysed reductive relay hydroboration of allylic alcohols is described. Commercially available nBuLi was found to be a robust transition metal-free initiator for this protocol, affording various boronic esters in high yield and selectivity. Mechanistically, this methodology involves a one-pot three-step successive process (dehydrocoupling/allylic hydride substitution/anti-Markovnikov hydroboration).
- Wang, Zi-Chao,Shen, Di,Gao, Jian,Jia, Xian,Xu, Youjun,Shi, Shi-Liang
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supporting information
p. 8848 - 8851
(2019/08/01)
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- Iron-Catalyzed Remote Arylation of Aliphatic C-H Bond via 1,5-Hydrogen Shift
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Catalytic amounts of an iron(III) salt and a N-heterocyclic carbene ligand catalyze the arylation of 2-iodoalkylarenes with diphenylzinc selectively at the C-H bond of the alkyl side chain. Several lines of evidence suggest that the iron catalyst reacts with the aryl iodide moiety of the substrate to generate an aryliron intermediate that behaves in a radical manner and cleaves the aliphatic C-H bond through 1,5-hydrogen transfer; the resulting alkyliron intermediate undergoes reductive elimination to give the arylated product.
- Zhou, Bingwei,Sato, Hiroki,Ilies, Laurean,Nakamura, Eiichi
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- Cross-coupling method of alkyl chloride and phenyl magnesium bromide
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The invention provides a cross-coupling method of an alkyl chloride and phenyl magnesium bromide, wherein a copper salt is used as a catalyst, the 2-methyltetrahydrofuran solution of phenyl magnesiumbromide is used as a coupling reagent, and the corss-coupling of the inactive secondary/tertiary alkyl chloride and the phenyl magnesium bromide is achieved. According to the present invention, the method has the high yield, does not require the addition of the ligand, is simple and easy to perform, and has important significance in the synthesis of complex molecules such as natural products, chiral drugs, and the like.
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-
Paragraph 0023; 0024; 0025
(2018/07/28)
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- Nickel-Catalyzed Reductive Cross-Coupling of Aryl Halides with Monofluoroalkyl Halides for Late-Stage Monofluoroalkylation
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A combinatorial nickel-catalyzed monofluoroalkylation of aryl halides with unactivated fluoroalkyl halides by reductive cross-coupling has been developed. This method demonstrated high efficiency, mild conditions, and excellent functional-group tolerance, thus enabling the late-stage monofluoroalkylation of diverse drugs. The key to success was the combination of diverse readily available bidentate and monodentate pyridine-type nitrogen ligands with nickel, which in situ generated a variety of readily tunable catalysts to promote fluoroalkylation with broad scope with respect to both coupling partners. This combinatorial catalysis strategy offers a solution for nickel-catalyzed reductive cross-coupling reactions and provides an efficient way to synthesize fluoroalkylated druglike molecules for drug discovery.
- Sheng, Jie,Ni, Hui-Qi,Zhang, Hao-Ran,Zhang, Kai-Fan,Wang, Yi-Ning,Wang, Xi-Sheng
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supporting information
p. 7634 - 7639
(2018/06/26)
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- Photochemical Nickel-Catalyzed Reductive Migratory Cross-Coupling of Alkyl Bromides with Aryl Bromides
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A novel method to access 1,1-diarylalkanes from readily available, nonactivated alkyl bromides and aryl bromides via visible-light-driven nickel and iridium dual catalysis, wherein diisopropylamine (iPr2NH) is used as the terminal stoichiometric reductant, is reported. Both primary and secondary alkyl bromides can be successfully transformed into the migratory benzylic arylation products with good selectivity. Additionally, this method showcases tolerance toward a wide array of functional groups and the presence of bases.
- Peng, Long,Li, Zheqi,Yin, Guoyin
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supporting information
p. 1880 - 1883
(2018/04/16)
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- Copper-catalyzed cross-coupling reactions of non-activated primary, secondary or tertiary alkyl chlorides with phenylmagnesium bromide
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Efficient copper-catalyzed cross-coupling reactions of non-activated alkyl chlorides, including primary, secondary, and tertiary alkyl chlorides, with phenyl Grignard reagents were achieved. Preparation of phenylmagnesium bromide in 2-methyltetrahydrofuran is critical for the success of the reaction. This protocol expands the synthetic toolbox for the construction of C[sbnd]C bonds of non-activated primary, secondary, and tertiary alkyl chlorides via copper-catalyzed cross-coupling.
- Tao, Chuanzhou,Sun, Lei,Wang, Bin,Liu, Zhou,Zhai, Yadong,Zhang, Xiulian,Shi, Dahua,Liu, Weiwei
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supporting information
p. 305 - 308
(2017/01/03)
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- From Dimethylamine to Pyrrolidine: The Development of an Improved Nickel Pincer Complex for Cross-Coupling of Nonactivated Secondary Alkyl Halides
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Replacement of a dimethyl amino group of the amidobis(amine) nickel(II) pincer complex (1), [(MeN2N)Ni-Cl], by a pyrrolidino group resulted in a new nickel(II) pincer complex (2), [(PyrNMeNN)Ni-Cl]. Complex 2 is an efficient catalyst for Kumada and Suzuki-Miyaura cross-coupling of nonactivated secondary alkyl halides, while complex 1 is largely inactive. The significant activity difference is tentatively attributed to a minimal structural difference, which leads to a more hemilabile ligand.
- Perez Garcia, Pablo M.,Di Franco, Thomas,Epenoy, Alexandre,Scopelliti, Rosario,Hu, Xile
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p. 258 - 261
(2016/01/12)
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- Phosphido- and Amidozirconocene Cation-Based Frustrated Lewis Pair Chemistry
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Methyl abstraction from neutral [Cp2ZrMe(ERR)] complexes 1 (E = N, P; R, R'; = alkyl, aryl) with either B(C6F5)3 or [Ph3C][B(C6F5)4] results in the formation of [Cp2Zr(ERR′)][X] complexes 2 (X- = MeB(C6F5)3-, B(C6F5)4-). The X-ray structure of amido complexes [Cp2Zr(NPh2)][MeB(C6F5)3] (2d) and [Cp2Zr(NtBuAr)][B(C6F5)4] (2e′, Ar = 3,5-C6H3(CH3)2) is reported, showing a sterically dependent Zr/N' interaction. Complexes 2 catalyze the hydrogenation of electron-rich olefins and alkynes under mild conditions (room temperature, 1.5 bar H2). Complex 2e binds CO2, giving [Cp2Zr(CO2)(NtBuAr)]2[MeB(C6F5)3]2 (3e). Amido complex 2d reacts with benzaldehyde yielding [Cp2Zr(OCH2Ph)((OC)PhNPh2)][MeB(C6F5)3] (7d). Phosphido complex [Cp2Zr(PCy2)][MeB(C6F5)3] (2a) reacts with diphenylacetylene to yield frustrated Lewis pair [Cp2Zr(PhCCPh)(PCy2)][MeB(C6F5)3] (8a) which further reacts with a range of carbonyl substrates.
- Normand, Adrien T.,Daniliuc, Constantin G.,Wibbeling, Birgit,Kehr, Gerald,Le Gendre, Pierre,Erker, Gerhard
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supporting information
p. 10796 - 10808
(2015/09/28)
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- Cross-coupling of nonactivated primary and secondary alkyl halides with aryl Grignard reagents catalyzed by chiral iron pincer complexes
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Iron(III) bisoxazolinylphenylamido (bopa) pincer complexes are efficient precatalysts for the cross-coupling of nonactivated primary and secondary alkyl halides with phenyl Grignard reagents. The reactions proceed at room temperature in moderate to excellent yields. A variety of functional groups can be tolerated. The enantioselectivity of the coupling of secondary alkyl halides is low.
- Bauer, Gerald,Cheung, Chi Wai,Hu, Xile
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p. 1726 - 1732
(2015/06/16)
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- Iron pincer complexes as catalysts and intermediates in alkyl-aryl kumada coupling reactions
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Iron-catalyzed alkyl-aryl Kumada coupling has developed into an efficient synthetic method, yet its mechanism remains vague. Here, we apply a bis(oxazolinylphenyl)amido pincer ligand (Bopa) to stabilize the catalytically active Fe center, resulting in isolation and characterization of well-defined iron complexes whose catalytic roles have been probed and confirmed. Reactivity studies of the iron complexes identify an Fe(II) "ate" complex, [Fe(Bopa-Ph)(Ph)2]-, as the active species for the oxidative addition of alkyl halide. Experiments using radical-probe substrates and DFT computations reveal a bimetallic and radical mechanism for the oxidative addition. The kinetics of the coupling of an alkyl iodide with PhMgCl suggests that formation of the "ate" complex, rather than oxidative addition, is the turnover-determining step. This work provides insights into iron-catalyzed cross-coupling reactions of alkyl halides.
- Bauer, Gerald,Wodrich, Matthew D.,Scopelliti, Rosario,Hu, Xile
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supporting information
p. 289 - 298
(2015/01/30)
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- Iron-catalyzed cross-coupling of unactivated secondary alkyl thio ethers and sulfones with aryl grignard reagents
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The first systematic investigation of unactivated aliphatic sulfur compounds as electrophiles in transition-metal-catalyzed cross-coupling are described. Initial studies focused on discerning the structural and electronic features of the organosulfur substrate that enable the challenging oxidative addition to the C(sp3)-S bond. Through extensive optimization efforts, an Fe(acac)3-catalyzed cross-coupling of unactivated alkyl aryl thio ethers with aryl Grignard reagents was realized in which a nitrogen "directing group" on the S-aryl moiety of the thio ether served a critical role in facilitating the oxidative addition step. In addition, alkyl phenyl sulfones were found to be effective electrophiles in the Fe(acac) 3-catalyzed cross-coupling with aryl Grignard reagents. For the latter class of electrophile, a thorough assessment of the various reaction parameters revealed a dramatic enhancement in reaction efficiency with an excess of TMEDA (8.0 equiv). The optimized reaction protocol was used to evaluate the scope of the method with respect to both the organomagnesium nucleophile and sulfone electrophile.
- Denmark, Scott E.,Cresswell, Alexander J.
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p. 12593 - 12628
(2014/01/17)
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- Efficient palladium-catalyzed C-O hydrogenolysis of benzylic alcohols and aromatic ketones with polymethylhydrosiloxane
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A simple method has been developed for the reductive deoxygenation of aromatic ketones and benzylic alcohols in the presence of polymethylhydrosiloxane (PMHS). The reductive deoxygenation of aromatic ketones and benzylic alcohols, including secondary alcohols, to the corresponding methylene hydrocarbons has been achieved in good to excellent yields using palladium chloride (PdCl2) as catalyst and PMHS as hydride source. Such deoxygenations were successfully with aryl alkyl ketones and diaryl ketones, as exemplified by the reductive deoxygenation of acetophenone and benzopheneone, respectively. The corresponding benzylic alcohols and secondary alcohol analogues could also be converted into their respective methylene hydrocarbons by the PdCl2/PMHS system.
- Wang, Hu,Li, Li,Bai, Xing-Feng,Shang, Jun-Yan,Yang, Ke-Fang,Xu, Li-Wen
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supporting information
p. 341 - 347
(2013/05/08)
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- Nickel-catalyzed reductive hydroesterification of styrenes using CO 2 and MeOH
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Complexes [(dippe)Ni(μ-H)]2 (A) (dippe = 1,2-bis-di- isopropylphosphino)ethane) and [(dtbpe)Ni(μ-H)]2 (B) (dtbpe = 1,2-bis-di-tert-butylphospino)ethane) catalyze the reductive hydroesterification of styrenes with the use of CO2 and MeOH. The latter acts as a hydrogen source and as an esterificating agent, to yield the corresponding branched and linear esters in moderate to good yields. In all of the studied reactions the linear esters were obtained in higher amounts than the branched ones. When the hydroesterification reaction was carried out using a stoichiometric metal/substrate ratio, the complexes [(P-P)Ni(CO)2] and [(P-P)Ni(CO3)] (P-P = dippe or dtbpe) were isolated and characterized by standard spectroscopic methods. Compounds [(dtbpe)Ni(CO) 2] and [(dtbpe)Ni(CO3)] were also fully characterized by single-crystal X-ray diffraction.
- Gonzalez-Sebastian, Lucero,Flores-Alamo, Marcos,Garcia, Juventino J.
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p. 8200 - 8207
(2013/02/22)
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- Cross-coupling of non-activated chloroalkanes with aryl grignard reagents in the presence of iron/N-heterocyclic carbene catalysts
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An efficient and high-yielding cross-coupling reaction of various primary, secondary, and tertiary alkyl chlorides with aryl Grignard reagents was achieved by using catalytic amounts of N-heterocyclic carbene ligands and iron salts. This reaction is a simple and efficient arylation method having applicability to a wide range of industrially abundant chloroalkanes, including polychloroalkanes, which are challenging substrates under conventional cross-coupling conditions.
- Ghorai, Sujit K.,Jin, Masayoshi,Hatakeyama, Takuji,Nakamura, Masaharu
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supporting information; experimental part
p. 1066 - 1069
(2012/04/10)
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- Comparison of the regiochemical behavior of zirconium and hafnium in the polyinsertion of styrenes
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The hafnocene-based catalyst ethylenebis(1-indenyl)hafnium dichloride/methylalumoxane, as well as its zirconium analogue, is able to oligomerize styrene, p-methylstyrene, and p-tert-butylstyrene in the presence of hydrogen to produce hydrooligomers. The c
- Galdi, Nunzia,Izzo, Lorella,Oliva, Leone
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experimental part
p. 4434 - 4439
(2011/01/07)
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- Iron-catalyzed cross-coupling of alkyl sulfonates with arylzinc reagents
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Iron-catalyzed cross-coupling reactions of primary and secondary alkyl sulfonates with arylzinc reagents proceed smoothly In the presence of excess TMEDA and a concomitant magnesium salt. The arylzinc reagents are prepared from the corresponding aryllithium or magnesium reagents with ZnI2. The In situ formation of alkyl Iodides and consecutive rapid cross-coupling avoids discrete preparation of the unstable secondary alkyl halides and also achieves high product selectivity.
- Ito, Shingo,Fujiwara, Yu-Ichi,Nakamura, Eiichi,Nakamura, Masaharu
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supporting information; experimental part
p. 4306 - 4309
(2009/12/26)
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- Determination of rate constants in the carbocationic polymerization of styrene: Effect of temperature, solvent polarity, and lewis acid
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The electrophilicity parameter (E = 9.6) of the 1-phenylethyl cation, 1+, has been determined and combined with the nucleophilicity parameter (N = 0.78, s = 0.95) of styrene (St) to predict diffusion-limited propagation in the cationic polymerization of St by the linear free energy relationship log k = s(N + E). This prediction has been experimentally verified using two different diffusion clock methods, which provided a value of k p± ≈ 2 × 109 L mol-1 s-1, 6 orders of magnitude higher than previously accepted, for the absolute rate constant of propagation of the TiCl4-induced polymerization of St in methyl cyclohexane/methyl chloride 60/40 (v/v) at -80°C. The kp± value remained unchanged in the temperature range -50 to -80°C, indicating that propagation does not have an enthalpic barrier; however, it increased moderately with increasing solvent polarity. The nature of the Lewis acid has little effect on kp ± as similar values have been obtained with TiCl4 or SnCl4. The apparent rate constant of ionization, k iapp, the rate constant of deactivation, k-i, and the apparent equilibrium constant of ionization, Ki app, have also been determined as a function of temperature. The kiapp increases slightly and k-i increases moderately with increasing temperature; therefore, Kiapp and the overall polymerization rate decrease moderately with increasing temperature.
- De, Priyadarsi,Faust, Rudolf,Schimmel, Holger,Ofial, Armin R.,Mayr, Herbert
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p. 4422 - 4433
(2007/10/03)
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- Regiochemistry of the styrene insertion with CH2-bridged ansa-zirconocene-based catalysts
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Methylenebis(indenyl)zirconium dichloride substituted in C(3), activated by methylalumoxane, is able to give polystyrene and ethylene-styrene copolymers. In this study hydrooligomers, whose structure, determined by 13C NMR and GC-MS techniques, gives information about the regiochemistry and the stereochemistry of styrene insertion, have been purposefully prepared. The regiochemistry of the styrene insertion is related to the encumbrance of substituents in C(3). rac-[Methylene-(3-R-1-indenyl)2]ZrCl2 with R = H, CH3, or CH2CH3 induces a prevailingly secondary styrene insertion into the zirconium-carbon bond. With increasing the substituent's steric hindrance (R = CH(CH3)2), regiochemistry inversion occurs and the primary insertion becomes prevailing. The analysis of ethylene-styrene copolymers obtained in the presence of the different catalysts allows confirming the correlation between regiochemistry and comonomers' reactivity. Besides, also the stereospecificity can be evaluated from the structure of the hydrotrimers, when the insertion is primary. Whereas the isospecificity in the absence of substituents (secondary insertion) and in the presence of the tert-butyl substituent (primary insertion) is well-known, a surprising syndiospecificity is observed when the indenyl ligand bears the isopropyl substituent in C(3).
- Izzo, Lorella,Napoli, Mariagrazia,Oliva, Leone
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p. 9340 - 9345
(2007/10/03)
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- Synthesis and transformations of metallacycles 20.* Cp2ZrCl2-catalyzed cycloalumination of arylolefins with AlEt3
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The Cp2ZrCl2-catalyzed reaction of arylolefins (styrene, o-and p-methylstyrenes, trans-stilbene, 1,4-diphenyl-1,3-butadiene) with AlEt3 resulting in mono-and disubstituted alumacyclopentanes and substituted alumacyclopropa
- Ibragimov,Khafizova,Satenov,Khalilov,Yakovleva,Rusakov,Dzhemilev
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p. 1574 - 1580
(2007/10/03)
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- The reactivity of the high-energy intermediates formed in the reactions of Group 13 metal atoms and aromatic alkenes
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Group 13 metal atoms were reacted with aromatic alkenes in a specialized metal atom reactor known as a "rotating cryostat." The nature of the intermediates formed was deduced from a GC-MS study of their hydrolysis and deuterolysis products. The product studies suggest that 2-phenylaluminacyclopropane, cis- and trans-3,4-diphenylaluminacyclopentane, and cis- and trans- 2,4-diphenylaluminacyclopentane are formed when A1 atoms react with styrene, and 2-methyl-2-phenylaluminacyclopropane and 3,4-dimethyl-3,4-diphenylaluminacyclopentane are formed when A1 atoms react with a-methylstyrene. These findings are consistent with the radicals detected in the EPR spectroscopic studies of A1-alkene reaction mixtures prepared under similar conditions. Mechanisms for the formation of the organoaluminium intermediates are discussed. Analogous organogallium intermediates are formed when gallium atoms react with styrene. The reductive coupling of styrene did not occur when In and T1 atoms were used. Only trace quantities of phenylethane were detected in the hydrolyzed reaction mixture.
- Joly, Helen A.,Kepes, Maria,Roy, Natalie,Prpic, Jason
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p. 400 - 406
(2007/10/03)
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- Thermolysis of a Tertiary Alkoxyamine. Recombination and Disproportionation of α-Phenethyl/Diethyl Nitroxyl Radical Pairs
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Alkoxyamine 3 undergoes thermolysis only on heating to over 150 °C, ΔH? = 34.3 ± 1.6 kcal/mol and ΔS? = 0.8 ± 3.7 eu. The initially formed nitroxyl (6) and α-phenethyl radicals (5) mainly disproportionate to styrene plus diethylhydroxylamine (2) but they also recombine to starting material and undergo a new reaction, disproportionation to ethylbenzene plus nitrone (12). The latter reacts with the styrene product to yield oxazolidines 8 and 9. The competition between attack of 5, generated from azo-α-phenylethane (1), on 2 versus styrene allowed us to calculate a rate constant at 120 °C of 5 × 103 M-1 s-1 for H. transfer from diethylhydroxylamine to 5.
- Engel, Paul S.,Duan, Shaoming,Arhancet, Graciela B.
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p. 3537 - 3541
(2007/10/03)
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- Oligomerization process
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Oligomers are produced from unsaturated monomers. They contain terminal unsaturation and have a degree of polymerization of from 2 to 200. These oligomers are produced by the free radical polymerization of unsaturated monomers using as an initiator and/or chain transfer agent in the process a transition metal complex comprising a metal cation and at least one chelating agent, said transition metal complex being generally in accordance with formula (I), wherein M is a transition metal ion which can form hexa- or penta-coordinated structures and, when complexed in this manner, has two or more readily interconverted adjacent valence states, R is hydrogen or an organic group or a transition metal complex derived form formula (I) and L is a ligand or controlling the stability and electron transfer properties of the transition metal complex and consists of an electron pair donor (Lewis base) capable of coordination with the metal ion.
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- CATYLYTIC SYNTHESIS AND REACTIONS OF MAGNESIOCYCLOALKANES. 2. SYNTHESIS OF SUBSTITUTED MAGNESIOCYCLOPENTANES IN THE PRESENCE OF ZYRCONIUM COMPLEXES
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Catalytic cyclometallation of styrene, m-methylstyrene, p-tert-butylstyrene, and 1-hexene with di n-alkylmagnesium compounds (n-R2Mg, where R=C3H7, C4H9, C6H13) in the presence of Cp2Zr2Cl2 has been given high yields of 2,4-disubstituted magnesiocyclopentanes.The probable mode of formation of magnesiocyclopentanes, involving zirconocyclopentanes formed from Cp2ZrCl2, n-R2Mg, and the appropiate olefins as reactive intermediates in the cyclometallation, is discussed. Keywords: catalytic synthesis, substituted styrenes, alkenes, magnesium alkyls.
- Dzhemilev, U. M.,Sultanov, R. M.,Gaimaldinov, R. G.,Muslukhov, R. R.,Lomakina, S. I.,Tolstikov, G. A.
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p. 770 - 788
(2007/10/02)
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- Cobalt-catalysed dimerization of styrenes under syngas
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Under a pressure of synthesis gas, cobalt carbonyl in pyridine catalyses the dimerization of styrene to yield 1,3-diphenylbutane selectively.
- Fontaine, M.,Hubert, A. J.,Noels, A. F.,Demonceau, A.,Teyssie, P.
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p. C28 - C31
(2007/10/02)
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- Trimethylsilyl Cyanide - A Reagent for Umpolung, XVI. - Effect of Umpolung Moieties on the Diastereoselectivity of the Nucleophilic Acylation of α-Chiral Carbonyl Compounds
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Umpolung of benzaldehyde leads to derivatives 1a-h, which add to the aldehydes 2a and 2c as well as to the ketones 2b and 2d in high yields, if side reactions are excluded by proper choice of conditions.Determined with the acyloins 4 or their silyl ethers 5, the diastereoselectivity of this reaction depends only slightly on the groups used for umpolung (1e > 1c > 1d > 1a ca. 1b ca. 1g > 1h > 1f).Strong effects are observed for the substituents at the center of chirality of the electrophiles 2.Whereas a syn/anti selectivity of ca. 95:5 in products 4 and 5 is obtained by an α-phenyl group in 2, only a 52:48-71:29 ratio is produced by an α-ethyl group.In case of 4d the syn/anti ratio is raised from 63:37 to 80:20 by optimizing the conditions.The observed Cram selectivity is explained by the model of Anh. - Key Words: Umpolung/ Diastereoselectivity/ Acyloins/ Substituent effects/ Nucleophilic acylation
- Huenig, Siegfried,Marschner, Claus
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p. 1329 - 1340
(2007/10/02)
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- Regioselective and Diastereoselective Alkyl-Alkene and Alkene-Alkene Coupling Promoted by Zirconocene and Hafnocene
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The reaction of Cp2Zr(CH2CH2R1)2 with a monosubstituted terminal alkene (H2C=CHR2) can produce, in a highly regio- and diastereoselective manner, zirconacyclopentane derivatives; the trans-3,4-disubstituted derivatives may be formed to the extents of >98percent in cases where both R1 and R2 are alkyl, while the trans-2-aryl-4-alkyl derivatives may be formed to the extents of >98percent in the coupling between a monoalkyl-substituted olefin and styrene or its derivative.
- Swanson, Douglas R.,Rousset, Christophe J.,Negishi, Ei-ichi,Takahashi, Tamotsu,Seki, Takashi,et al.
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p. 3521 - 3523
(2007/10/02)
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- Reactions of electrophilic transition metal cations with olefins and small ring compounds. Rearrangements and polymerizations
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The reactivity of the cationic, weakly ligated, tranisition metal compounds, (BF4)2 (1); (BF4)2, (M = Ni, 2; Co, 3); (BF4)2, (M = Mo, 4; W, 5), vis-a-vis olefins and strained ring compounds was studied.A number of these species were observed to form a charge-transfer complex with tetra-p-anisylethylene.These compounds were also found to catalyze the skeletal rearrangement and polymerization of appropriately substituted olefins and cyclopropanes.These reactions appear to be initiated by the electrophilic (heterolytic) cleavage of either the ?-bond of the olefin or a strained C-C ?-bond of the small ring compound.
- Sen, Ayusman,Lai, Ta-Wang,Thomas, Richard R.
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p. 567 - 588
(2007/10/02)
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- Process for introduction of styrenes in side chain of substituted aromatic compounds
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A process for introduction of styrenes in the side chain of substituted aromatic compounds, said side chain containing at least one hydrogen atom in the α-position thereof, is disclosed, comprising reacting the styrenes and the substituted aromatic compounds in the presence of (A) an alkali metal and (B) a compound containing a benzyloxy group or alkyl and/or aryl-substituted benzyloxy group. Use of (A) and (B) as a reaction accelerator permits to introduce the styrenes in the side chain of the substituted aromatic compounds in high yield and selectivity.
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- Anodic Oxidation of Organoboranes
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Organoboranes are converted into more easily oxidizable borates by reaction with nucleophiles and the alkyl groups are dimerized by anodic oxidation.The oxidation potentials (Ep) of the borates depend strongly on the nature of the complexing nucleophile, for instance Ep = +0.37 V (vs.SCE) with OH- or +1.65 V with tetrahydrofuran.The dimer yields are optimized with trioctylborane (5) by variation of the electrode material and the elctrolyte.At the platinum anode in sodium hydroxide-methanol/tetrahydrofuran yields of 80percent are obtained for acyclic alkyl groups, and lo wer ones for cycloalkyl groups.They exceed those obtained by the Kolbe electrolysis or the oxidation with neutral hydrogen peroxide and they are comparable to those of the AgNO3 oxidation. - The selective preparation of unsymmetrical products from borates with different alkyl groups is not possible, the dimerization proceeds likely via free radicals that couple statistically.Good yields of unsymmetrical coupling products are achieved, when one olefin is used in excess.With choro-, ethoxy-, acetoxy-, and aryl-substituted alkyl groups the dimers are obtained in 21 - 66percent yield, with bromide the yield are lower and with nitriles the dimerization fails.
- Schlegel, Guenter,Schaefer, Hans J.
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p. 1400 - 1423
(2007/10/02)
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- FORMATION OF SULPHUR COMPOUNDS DURING THE HYDRODENITROGENATION OF ANILINE, CYCLOHEXYLAMINE, BENZYLAMINE, AND 2-PHENYLETHYLAMINE ON A NICKEL-TUNGSTEN CATALYST IN THE PRESENCE OF HYDROGEN SULPHIDE
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Hydrodenitrogenations of aniline, cyclohexylamine, benzylamine, and 2-phenylethylamine were performed on a sulphided nickel-tungsten catalyst at 300 deg C in an autoclave filled with hydrogen in the absence and in the presence of hydrogen sulphide.Due to the presence of hydrogen sulphide the degree of conversion increased from 0.9 to 3,6percent for aniline and from 72 to 99percent for benzylamine, and the fraction of neutral substances increased from 2.4 to 7percent for cyclohexylamine and from 5.0 to 8.9percent for 2-phenylethylamine.The neutral fractions contained cyclohexanethiol, thiobenzamide, 2-phenylethanethiol, and other sulphur compounds giving evidence that the increased degree of conversion of the amines was due to the hydrogen sulphide taking direct part in the chemical reaction.
- Cerny, Mirko,Trka, Antonin
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p. 2387 - 2392
(2007/10/02)
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- Carbanion Rearrangements by Intramolecular 1,ω Proton Shifts, III. The Reaction of 2-, 3-, 4-, and 5-Phenylalkyllithium Compounds
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Upon addition of THF to a solution of 4-phenylbutyllithium (2) in diethyl ether a rapid intramolecular 1,4 proton shift takes place with the formation of 1-phenylbutyllithium (5).Similarly, although somewhat more slowly, 5-phenylpentyllithium (82) rearranges to 1-phenylpentyllithium (83) via 1,5 proton transfer.The corresponding rearrangements by 1,2 or 1,3 hydrogen shifts, however, starting with 2-phenylethyllithium (1) and 3-phenylpropyllithium (54), respectively, were not detected.With 3-phenylpropyllithium (54) a slow intramolecular 1,5 transfer an ortho proton is observed instead, yielding o-propylphenyllithium (100).The corresponding 1,6 shift with 4-phenylbutyllithium (2) was also detected in a minor amount in addition to the 1,4 proton shift already mentioned.There is no indication, however, for a 1,4 transfer of an ortho proton in 2-phenylethyllithium (1).The reaction products in this case can be exclusively explained by intermolecular transmetallation reactions.All ω-phenylalkyllithium compounds under investigation show interesting side and secondary reactions being rather different in deuterated solvents and in deuteriumfree solvents, respectively, due to the isotope effects.The analysis of the products is accomplished by 1H-NMR spectroscopy and, after derivatization, with the help of a GC-MS-combination.Stereoelectronic reasons are made responsible for the failure of the intramolecular 1,2 and 1,3 proton shift in these systems.
- Maercker, Adalbert,Passlack, Michael
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p. 540 - 577
(2007/10/02)
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- Addition Reactions of Benzothiophen. Part 1. Self-addition and Addition of Simple Aromatic Hydrocarbons
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Benzothiophen undergoes facile addition reactions across the 2,3-bond when treated with aluminium chloride in an appropriate solvent at 0 or 20 deg C.In carbon disulphide or dichloromethane, it undergoes self-addition to give two or more of the four possible 2- or 3-(2- or 3-benzothienyl)2,3-dihydrobenzothiophens (3)-(6).In the presence of an aromatic solvent, the dimerization reaction just mentioned predominates at low temperatures (0 deg C or below), or at room temperature if the solvent is benzene, chlorobenzene, t-butylbenzene, isopropylbenzene, or 1,3,5-trimethylbenzene.At room temperature, in toluene, ethylbenzene, and 1,2- or 1,4-dimethylbenzene, solvent addition occurs to give a mixture of the corresponding 2- and 3-aryl-2,3-dihydrobenzenethiophens.At 80 deg C, benzene and toluene give the fully aromatic 2-arylbenzothiophen.The reactions are discussed in terms of an ionic mechanism involving protonation of benzothiophen by moist aluminium chloride and reaction of the resulting electrophile with benzothiophen or with an aromatic substrate.
- Clark, Peter David,Clarke, Kenneth,Ewing, David F.,Scrowston, Richard M.
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p. 677 - 685
(2007/10/02)
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