1007-26-7Relevant academic research and scientific papers
Reactivity of mixed organozinc and mixed organocopper reagents: 6. Nickel-catalyzed coupling of methylarylzincs with primary alkyl halides; An atom-economic aryl-alkyl coupling
Pekel, ?zgen ?mür,Erdik, Ender
, p. 7087 - 7090 (2011)
A nickel-catalyzed process for the cross-coupling of mixed arylzincs and primary alkyl halides has been developed. The reaction of a methylarylzinc with a primary alkyl halide in THF in the presence of NiCl2/PPh 3 takes place with selective aryl transfer at room temperature in moderate yields. This protocol provides an atom-economic alternative to aryl-primary alkyl coupling using diarylzincs.
Photochemistry of substituted benzyl acetates and benzyl pivalates: A reinvestigation of substituent effects
Hilborn,MacKnight,Pincock,Wedge
, p. 3337 - 3346 (1994)
The photosolvolysis reactions, in methanol, of six substituted benzyl acetates (7a-f) and benzyl pivalates (8a-f) were studied. Five major benzylic products were formed from two critical intermediates. The ethers (9) were formed from the ion pair, 15, and all of the other products (10-14) were formed from the radical pair, 16. Quenching studies showed that only excited singlet state reactivity was important. The product yields were found to be highly substituent dependent. For instance, for the acetate esters, the yield of ether (9) varied from 2% for X = 4-OCH3 to 32% for X = 3-OCH3. Most of the differences in the yields could be attributed to ground state processes that occur after bond cleavage. The important competition is between electron transfer, converting the radical pair to the ion pair, and decarboxylation of RCO2*. The rates of electron transfer are shown to fit Marcus theory in both the normal and inverted regions. Direct heterolytic cleavage to form the ion pair is of minimal importance.
SELECTIVE COUPLING OF FREE RADICALS VIA ORGANOCHROMIUM COMPLEXES.
Sustmann, Reiner,Altevogt, Rudolf
, p. 5167 - 5170 (1981)
Free radicals can be coupled in high yield to give either symmetric dimers or cross coupling products by reacting chromous chloride in THF with alkyl halides.
On the Mechanism of the Reduction of Primary Halides with Grignard Reagents in the Presence of (dppf)PdCl2 or (dppf)Pd(0)
Yuan, Kaixu,Scott, William J.
, p. 6188 - 6194 (1990)
Reaction of primary alkyl halides with Grignard reagents in the presence (dppf)PdCl2 or (dppf)Pd(0) leads to reduction of the halide.The mechanism of the reduction is dependent on the solvent and the Grignard reagent.In tetrahydrofuran, reduction is independent of palladium.The alkyl halide is largely reduced by β-hydride transfer from the Grignard reagent.Competing with hydride transfer is a halogen-metal exchange reaction, which converts the alkyl halide into the corresponding Grignard reagent.Protonation of reaction mixture then gives the observed products.Grignard reagents that do not possess β-hydrogens undergo the halogen-metal exchange exclusively, but still lead to reduction of the alkyl halide.At subambient temperatures and in diethyl ether, reduction of primary alkyl halides with Grignard reagents in the absence of palladium catalysts is very slow.That reduction which does occur is almost exclusively the product of β-hydride transfer.The addition of (dppf)PdCl2 markedly accelerates the rate of reduction of alkyl halides in diethyl ether.The catalytic effect is proposed to occur through a catalytic cycle involving oxidative addition of the alkyl halide, hydride-transfer, and reductive-elimination steps.The order of the first two steps remains unclear.
Site-Specific Alkene Hydromethylation via Protonolysis of Titanacyclobutanes
Bartfield, Noah M.,Frederich, James H.,Law, James A.
supporting information, p. 14360 - 14364 (2021/05/27)
Methyl groups are ubiquitous in biologically active molecules. Thus, new tactics to introduce this alkyl fragment into polyfunctional structures are of significant interest. With this goal in mind, a direct method for the Markovnikov hydromethylation of alkenes is reported. This method exploits the degenerate metathesis reaction between the titanium methylidene unveiled from Cp2Ti(μ-Cl)(μ-CH2)AlMe2 (Tebbe's reagent) and unactivated alkenes. Protonolysis of the resulting titanacyclobutanes in situ effects hydromethylation in a chemo-, regio-, and site-selective manner. The broad utility of this method is demonstrated across a series of mono- and di-substituted alkenes containing pendant alcohols, ethers, amides, carbamates, and basic amines.
Reductive Deamination with Hydrosilanes Catalyzed by B(C6F5)3
Fang, Huaquan,Oestreich, Martin
supporting information, p. 11394 - 11398 (2020/05/25)
The strong boron Lewis acid tris(pentafluorophenyl)borane B(C6F5)3 is known to catalyze the dehydrogenative coupling of certain amines and hydrosilanes at elevated temperatures. At higher temperature, the dehydrogenation pathway competes with cleavage of the C?N bond and defunctionalization is obtained. This can be turned into a useful methodology for the transition-metal-free reductive deamination of a broad range of amines as well as heterocumulenes such as an isocyanate and an isothiocyanate.
Carbonyl and olefin hydrosilylation mediated by an air-stable phosphorus(iii) dication under mild conditions
Andrews, Ryan J.,Chitnis, Saurabh S.,Stephan, Douglas W.
supporting information, p. 5599 - 5602 (2019/05/21)
The readily-accessible, air-stable Lewis acid [(terpy)PPh][B(C6F5)4]21 is shown to mediate the hydrosilylation of aldehydes, ketones, and olefins. The utility and mechanism of these hydrosilylations are considered.
Mechanistic Characterization of (Xantphos)Ni(I)-Mediated Alkyl Bromide Activation: Oxidative Addition, Electron Transfer, or Halogen-Atom Abstraction
Diccianni, Justin B.,Katigbak, Joseph,Hu, Chunhua,Diao, Tianning
supporting information, p. 1788 - 1796 (2019/01/26)
Ni(I)-mediated single-electron oxidative activation of alkyl halides has been extensively proposed as a key step in Ni-catalyzed cross-coupling reactions to generate radical intermediates. There are four mechanisms through which this step could take place: oxidative addition, outer-sphere electron transfer, inner-sphere electron transfer, and concerted halogen-atom abstraction. Despite considerable computational studies, there is no experimental study to evaluate all four pathways for Ni(I)-mediated alkyl radical formation. Herein, we report the isolation of a series of (Xantphos)Ni(I)-Ar complexes that selectively activate alkyl halides over aryl halides to eject radicals and form Ni(II) complexes. This observation allows the application of kinetic studies on the steric, electronic, and solvent effects, in combination with DFT calculations, to systematically assess the four possible pathways. Our data reveal that (Xantphos)Ni(I)-mediated alkyl halide activation proceeds via a concerted halogen-atom abstraction mechanism. This result corroborates previous DFT studies on (terpy)Ni(I)- and (py)Ni(I)-mediated alkyl radical formation, and contrasts with the outer-sphere electron transfer pathway observed for (PPh3)4Ni(0)-mediated aryl halide activation. This study of a model system provides insight into the overall mechanism of Ni-catalyzed cross-coupling reactions and offers a basis for differentiating electrophiles in cross-electrophile coupling reactions.
Photoredox-Assisted Reductive Cross-Coupling: Mechanistic Insight into Catalytic Aryl-Alkyl Cross-Couplings
Paul, Avishek,Smith, Mark D.,Vannucci, Aaron K.
, p. 1996 - 2003 (2017/02/26)
Here, we describe a photoredox-assisted catalytic system for the direct reductive coupling of two carbon electrophiles. Recent advances have shown that nickel catalysts are active toward the coupling of sp3-carbon electrophiles and that well-controlled, light-driven coupling systems are possible. Our system, composed of a nickel catalyst, an iridium photosensitizer, and an amine electron donor, is capable of coupling halocarbons with high yields. Spectroscopic studies support a mechanism where under visible light irradiation the Ir photosensitizer in conjunction with triethanolamine are capable of reducing a nickel catalyst and activating the catalyst toward cross-coupling of carbon electrophiles. The synthetic methodology developed here operates at low 1 mol % catalyst and photosensitizer loadings. The catalytic system also operates without reaction additives such as inorganic salts or bases. A general and effective sp2-sp3 cross-coupling scheme has been achieved that exhibits tolerance to a wide array of functional groups.
Decarboxylative Cross-Electrophile Coupling of N-Hydroxyphthalimide Esters with Aryl Iodides
Huihui, Kierra M. M.,Caputo, Jill A.,Melchor, Zulema,Olivares, Astrid M.,Spiewak, Amanda M.,Johnson, Keywan A.,Dibenedetto, Tarah A.,Kim, Seoyoung,Ackerman, Laura K. G.,Weix, Daniel J.
, p. 5016 - 5019 (2016/05/19)
A new method for the decarboxylative coupling of alkyl N-hydroxyphthalimide esters (NHP esters) with aryl iodides is presented. In contrast to previous studies that form alkyl radicals from carboxylic acid derivatives, no photocatalyst, light, or arylmetal reagent is needed, only nickel and a reducing agent (Zn). Methyl, primary, and secondary alkyl groups can all be coupled in good yield (77% ave yield). One coupling with an acid chloride is also presented. Stoichiometric reactions of (dtbbpy)Ni(2-tolyl)I with an NHP ester show for the first time that arylnickel(II) complexes can directly react with NHP esters to form alkylated arenes.
