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Nickel-catalyzed reductive deoxygenation of diverse C-O bond-bearing functional groups
We report a catalytic method for the direct deoxygenation of various C-O bond-containing functional groups. Using a Ni(II) pre-catalyst and silane reducing agent, alcohols, epoxides, and ethers are reduced to the corresponding alkane. Unsaturated species including aldehydes and ketones are also deoxygenated via initial formation of an intermediate silylated alcohol. The reaction is chemoselective for C(sp3)-O bonds, leaving amines, anilines, aryl ethers, alkenes, and nitrogen-containing heterocycles untouched. Applications toward catalytic deuteration, benzyl ether deprotection, and the valorization of biomass-derived feedstocks demonstrate some of the practical aspects of this methodology.
Cook, Adam,MacLean, Haydn,St. Onge, Piers,Newman, Stephen G.
p. 13337 - 13347
(2021/11/20)

Palladium supported on structurally stable phenanthroline-based polymer nanotubes as a high-performance catalyst for the aqueous Suzuki-Miyaura coupling reaction
Though the Suzuki-Miyaura coupling reaction has intrinsic advantages in organic synthesis, it is still a challenging task to develop a highly active and truly heterogeneous catalyst for the aqueous Suzuki-Miyaura coupling reaction (SMR). In this work, a series of phenanthroline-based polymers (PBPs; PBP1 to PBP8) were synthesized by a simple one-step AlCl3-catalyzed Friedel-Crafts polymerization method. Systematic measurements of PBPs by N2adsorption-desorption isotherms, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA) show that most of the PBPs have a nanosheet morphology, except PBP8 which has both one-dimensional nanotubular morphology and large surface area (745 m2g?1). Benefitting from the porous nanotube morphology and the two N atoms contained in the phenanthroline unit of the polymer structure, polymer PBP8 shows adsorption effects and strong chelating stabilization on the Pd active metal (size, 2-5 nm). The Pd/PBP8 catalyst exhibits superior catalytic activity within 2 h (TOF value: 3077 h?1) and reusability (7 cycles) in the SMR with typical reactants such as bromobenzene, phenylboronic acid and the base of K3PO4.3H2O at 30 °C in a solvent mixture of water and ethanol (VH2O?:?Vethanol= 3?:?2).
Yang, Didi,Wang, Shuhui,Dan, Ting,Gao, Dashuang,Au, Chaktong,Zhang, Wanju,Zhang, Yan
p. 12120 - 12128
(2021/07/19)

Site-Specific Oxidation of (sp3)C-C(sp3)/H Bonds by NaNO2/HCl
A site-specific oxidation of (sp3)C-C(sp3) and (sp3)C-H bonds in aryl alkanes by the use of NaNO2/HCl was explored. The method is chemical-oxidant-free, transition-metal-free, uses water as the solvent, and proceeds under mild conditions, making it valuable and attractive to synthetic organic chemistry.
Zhao, Jianyou,Shen, Tong,Sun, Zhihui,Wang, Nengyong,Yang, Le,Wu, Jintao,You, Huichao,Liu, Zhong-Quan
supporting information
p. 4057 - 4061
(2021/05/26)

Metal-free synthesis of biarenes via photoextrusion in di(tri)aryl phosphates
A metal-free route for the synthesis of biarenes has been developed. The approach is based on the photoextrusion of a phosphate moiety occurring upon irradiation of biaryl- A nd triaryl phosphates. The reaction involves an exciplex as the intermediate and it is especially suitable for the preparation of electron-rich biarenes.
Qrareya, Hisham,Meazza, Lorenzo,Protti, Stefano,Fagnoni, Maurizio
supporting information
p. 3008 - 3014
(2021/01/18)

Generation of Alkyl Radical through Direct Excitation of Boracene-Based Alkylborate
The generation of tertiary, secondary, and primary alkyl radicals has been achieved by the direct visible-light excitation of a boracene-based alkylborate. This system is based on the photophysical properties of the organoboron molecule. The protocol is applicable to decyanoalkylation, Giese addition, and nickel-catalyzed carbon-carbon bond formations such as alkyl-aryl cross-coupling or vicinal alkylarylation of alkenes, enabling the introduction of various C(sp3) fragments to organic molecules.
Hashizume, Daisuke,Hosoya, Takamitsu,Nakamura, Kei,Ohmiya, Hirohisa,Sato, Yukiya,Sumida, Yuto
supporting information
p. 9938 - 9943
(2020/06/27)

C-C coupling formation using nitron complexes
A series of RuII (1), RhIII (2), IrIII (3, 4), IrI (5) and PdII (6-9) complexes of the 'instant carbene' nitron were prepared and characterized by 1H- and 13C-NMR, FT-IR and elemental analysis. The molecular structures of complexes 1-4 and 6 were determined by X-ray diffraction studies. The catalytic activity of the complexes (1-9) was evaluated in alpha(α)-alkylation reactions of ketones with alcohol via the borrowing hydrogen strategy under mild conditions. These complexes were able to perform this catalytic transformation in a short time with low catalyst and base amounts under an air atmosphere. Also, the PdII-nitron complexes (6-9) were applied in the Suzuki-Miyaura C-C coupling reaction and these complexes successfully initiated this reaction in a short time (30 minutes) using the H2O/2-propanol (1.5?:?0.5) solvent system. The DFT calculations revealed that the Pd0/II/0 pathway was more preferable for the mechanism
Sevim, Mehmet,Kavukcu, Serdar Batikan,Kinal, Arma?an,?ahin, Onur,Türkmen, Hayati
supporting information
p. 16903 - 16915
(2020/12/18)

Small organic molecules with tailored structures: Initiators in the transition-metal-free C-H arylation of unactivated arenes
Simple, small organic molecules containing nitrogen and oxygen atoms in their structures have been disclosed to catalyze transition-metal-free C-H arylation of unactivated arenes with aryl iodides in the presence of tBuOK. In this article, an optimized catalytically active molecule, (2-(methylamino)phenyl)methanol, was designed. A broad range of aryl iodides could be converted into the corresponding arylated products at 100 °C over 24 h with good to excellent yields. Mechanistic experiments verified that radicals participated in this catalytic transformation and that the cleavage of the aromatic C-H bond was not the rate determining step. A K+ capture experiment by 18-crown-6 emphasized the significance of the cation species of the strong base. Fourier transform infrared spectroscopy proved that the catalytic system was activated by the hydrogen bonds between small organic molecules and tBuOK. Also, a clear mechanism was proposed. This transition-metal-free method affords a promising system for efficient and inexpensive synthesis of biaryls via a user-friendly approach, as confirmed by scale-up experiments.
Chen, Suqing,Chen, Wenjun,Chen, Yu,Liu, Zhenghui,Mu, Tiancheng,Wang, Peng,Yan, Zhenzhong
p. 14500 - 14509
(2020/04/27)

Catalytic protodeboronation of pinacol boronic esters: Formal anti-Markovnikov hydromethylation of alkenes
Pinacol boronic esters are highly valuable building blocks in organic synthesis. In contrast to the many protocols available on the functionalizing deboronation of alkyl boronic esters, protodeboronation is not well developed. Herein we report catalytic protodeboronation of 1°, 2° and 3° alkyl boronic esters utilizing a radical approach. Paired with a Matteson-CH2-homologation, our protocol allows for formal anti-Markovnikov alkene hydromethylation, a valuable but unknown transformation. The hydromethylation sequence was applied to methoxy protected (-)-Δ8-THC and cholesterol. The protodeboronation was further used in the formal total synthesis of δ-(R)-coniceine and indolizidine 209B.
Clausen, Florian,Kischkewitz, Marvin,Bergander, Klaus,Studer, Armido
p. 6210 - 6214
(2019/06/27)

Alkyl Carbagermatranes Enable Practical Palladium-Catalyzed sp2-sp3 Cross-Coupling
Pd-catalyzed cross-coupling reactions have achieved tremendous accomplishments in the past decades. However, C(sp3)-hybridized nucleophiles generally remain as challenging coupling partners due to their sluggish transmetalation compared to the C(sp2)-hybridized counterparts. While a single-electron-transfer-based strategy using C(sp3)-hybridized nucleophiles had made significant progress recently, fewer breakthroughs have been made concerning the traditional two-electron mechanism involving C(sp3)-hybridized nucleophiles. In this report, we present a series of unique alkyl carbagermatranes that were proven to be highly reactive in cross-coupling reactions with our newly developed electron-deficient phosphine ligands. Generally, secondary alkyl carbagermatranes show slightly lower, yet comparable activity to its Sn analogue. Meanwhile, primary alkyl carbagermatranes exhibit high activity, and they were also proved stable enough to be compatible with various reactions. Chiral secondary benzyl carbagermatrane gave the coupling product under base/additive-free conditions with its configuration fully inversed, suggesting that transmetalation was carried out in an "SE2(open) Inv" pathway, which is consistent with Hiyama's previous observation. Notably, the cross-coupling of primary alkyl carbagermatranes could be performed under base/additive-free conditions with excellent functional group tolerance and therefore may have potentially important applications such as stapled peptide synthesis.
Xu, Meng-Yu,Jiang, Wei-Tao,Li, Ying,Xu, Qing-Hao,Zhou, Qiao-Lan,Yang, Shuo,Xiao, Bin
supporting information
p. 7582 - 7588
(2019/05/16)

Transition-Metal-Free C-C, C-O, and C-N Cross-Couplings Enabled by Light
Transition-metal-catalyzed cross-couplings to construct C-C, C-O, and C-N bonds have revolutionized chemical science. Despite great achievements, these metal catalysts also raise certain issues including their high cost, requirement of specialized ligands, sensitivity to air and moisture, and so-called "transition-metal-residue issue". Complementary strategy, which does not rely on the well-established oxidative addition, transmetalation, and reductive elimination mechanistic paradigm, would potentially eliminate all of these metal-related issues. Herein, we show that aryl triflates can be coupled with potassium aryl trifluoroborates, aliphatic alcohols, and nitriles without the assistance of metal catalysts empowered by photoenergy. Control experiments reveal that among all common aryl electrophiles only aryl triflates are competent in these couplings whereas aryl iodides and bromides cannot serve as the coupling partners. DFT calculation reveals that once converted to the aryl radical cation, aryl triflate would be more favorable to ipso substitution. Fluorescence spectroscopy and cyclic voltammetry investigations suggest that the interaction between excited acetone and aryl triflate is essential to these couplings. The results in this report are anticipated to provide new opportunities to perform cross-couplings.
Liu, Wenbo,Li, Jianbin,Querard, Pierre,Li, Chao-Jun
p. 6755 - 6764
(2019/05/06)

Nickel-catalyzed C-N bond activation: Activated primary amines as alkylating reagents in reductive cross-coupling
Nickel-catalyzed reductive cross coupling of activated primary amines with aryl halides under mild reaction conditions has been achieved for the first time. Due to the avoidance of stoichiometric organometallic reagents and external bases, the scope regarding both coupling partners is broad. Thus, a wide range of substrates, natural products and drugs with diverse functional groups are tolerated. Moreover, experimental mechanistic investigations and density functional theory (DFT) calculations in combination with wavefunction analysis have been performed to understand the catalytic cycle in more detail.
Yue, Huifeng,Zhu, Chen,Shen, Li,Geng, Qiuyang,Hock, Katharina J.,Yuan, Tingting,Cavallo, Luigi,Rueping, Magnus
p. 4430 - 4435
(2019/04/29)

Synthesis of 1,1′-diarylethanes and related systems by displacement of trichloroacetimidates with trimethylaluminum
Benzylic trichloroacetimidates are readily displaced by trimethylaluminum under Lewis acid promoted conditions to provide the corresponding methyl substitution product. This method is a convenient way to access 1,1′-diarylethanes and related systems, which play a significant role in medicinal chemistry, with a number of systems owing their biological activity to this functionality. Most benzylic substrates undergo ready displacement, with electron deficient systems being the exception. The use of an enantiopure imidate showed significant racemization, implicating the formation of a cationic intermediate.
Mahajani, Nivedita S.,Chisholm, John D.
p. 4131 - 4139
(2018/04/14)

Stable ferrocenyl-NHC Pd(II) complexes: Evidence of C-H ?H/π interaction and M-O bonding in solution
New air stable palladium(II)-NHC complexes where carbene ligand is substituted with a bulky ferrocenylmethyl and pyranylmethyl groups viz. PdI(Phpy){FcCH2-C3H2N2-Me} (3), PdI2{FcCH2-C3H2N2-C6H11O} (4) and PdI2{FcCH2-NHC}(L) (5–10) (NHC = C3H2N2-Me or C6H11O; L = pyridine, imidazole and thiazole) are reported. The presence of C-H?H/π interactions has been confirmed for complex 3 by NOE interaction and multinuclear NMR experiments. In addition, for this complex, a quantum chemical analysis was performed using PM3 semi-empirical calculations to find the possible conformers. The conformation with minimal energy confirms the NMR interpretation for complex 3. The M-O bond in complex 4 was ruptured by the reaction of an extra pyridine ligand to afford PdI2{FcCH2-C3H2N2-C6H11O}(py) (5) which was synthetized differently by reacting NHC ligand, Pd(OAc)2 and pyridine. Molecular structure of complex 5 was determined by X-ray diffraction. The catalytic activity of these complexes was checked in Suzuki-Miyaura reaction. Complex 5 exhibits excellent conversions and selectivities (up to 99%).
Azpiroz, Ramón,Sharma, Pankaj,Javier Pérez-Flores,Gutierrez, René,Espinosa-Pérez, Georgina,Lara-Ochoa, Francisco
p. 196 - 206
(2017/08/10)

Amide-ligand-controlled highly para-selective arylation of monosubstituted simple arenes with arylboronic acids
Pd-catalyzed highly para-selective arylations of monosubstituted simple arenes with arylboronic acids to widely existed biaryls have been developed. Inspired by requisite amide-directing groups in reported selective oxidative couplings, amide ligands, especially DMF, are designed and found to be critical for the selectivity control in current arylations.
Luan, Yu-Xin,Zhang, Tao,Yao, Wei-Wei,Lu, Ke,Kong, Lu-Yao,Lin, Yu-Tong,Ye, Mengchun
supporting information
p. 1786 - 1789
(2017/02/15)

N-Methylanilines as Simple and Efficient Promoters for Radical-Type Cross-Coupling Reactions of Aryl Iodides
Activation of the carbon–halogen bonds in aryl halides is a key step in transition-metal-free cross-coupling reactions. In this paper, a new and efficient radical initiation system for the activation of iodoarenes to produce aryl radicals was discovered, which employs the combination of N-methylanilines and tBuOK. This radical initiation system is robust and versatile, enabling various types of aryl-radical-related reactions.
Yang, Huan,Zhang, Li,Jiao, Lei
supporting information
p. 65 - 69
(2017/01/09)

Facile Hydrogenolysis of C(sp3)–C(sp3) σ Bonds
The modification of benzylic quaternary, tertiary, and secondary carbon centers through palladium-catalyzed hydrogenolysis of C(sp3)–C(sp3) σ bonds is presented. When benzyl Meldrum's acid derivatives bearing quaternary benzylic centers are treated under mild hydrogenolysis conditions – palladium on carbon and atmospheric pressure of hydrogen – aromatics substituted with tertiary benzylic centers and Meldrum's acid are obtained with good to excellent yield. Analogously, substrates containing tertiary or secondary benzylic centers yield aromatics substituted with secondary benzylic centers or toluene derivatives, respectively. Furthermore, this strategy is used for the high yielding synthesis of diarylmethanes. The scope of the reductive dealkylation reaction is explored and the limitations with respect to steric and electronic factors are determined. A mechanistic analysis of the reaction is described that consisted of deuterium labelling experiments and hydrogenolysis of enantioenriched derivatives. The investigation shows that the C(sp3)–C(sp3) σ bond-cleaving events occur through a hybrid SN1/SN2 mechanism, in which the palladium center displaces a carbon-based leaving group, namely Meldrum's acid, with inversion of configuration, followed by reductive elimination of palladium to furnish a C?H bond. (Figure presented.).
Fillion, Eric,Beaton, Eric,Nguyen, Yen,Wilsily, Ashraf,Bondarenko, Ganna,Jacq, Jér?me
supporting information
p. 3422 - 3434
(2016/11/13)

The isopropylation of biphenyl over transition metal substituted aluminophosphates: MAPO-5 (M: Co and Ni)
The isopropylation of biphenyl (BP) was examined over transition metal substituted aluminophosphates (MAPO-5; M: Co and Ni) with 12-membered (12-MR) oxygen ring pore-entrances of AFI topology. The MAPO-5 samples were synthesized by dry gel conversion method using trimethylamine as a structure directing agent, and their properties were characterized by XRD, XPS, SEM, N2 adsorption, NH3-TPD, pyridine adsorption, and o-xylene uptake. They are clear crystals without impurity phases and agglomerates, and found small amounts of Br?nsted acid sites which are expecting active for acid catalysis. The isopropylation of BP over both of Co(5)APO-5 and Ni(5)APO-5 at 250 °C gave the high selectivities for 4,4′-DIPB: 65-75%. 4-IPBP is almost exclusive precursor of 4,4′- and 3,4′-DIPB. 3-IPBP was not significantly concerned even though 3-IPBP was predominant among IPBP isomers at the late stages: the MAPO-5 channels allow preferential access of 4-IPBP, and prevent the access of 3-IPBP due to reactant selectivity mechanism. The selective formation of 4,4′-DIPB occurred by preferential exclusion of bulkier 3,4′-DIPB and other isomers through the steric interaction of transition states with the channels by the restricted transition state selectivity mechanism. MAPO-5 (M: Co and Ni) has the same level of the selectivities for 4,4′-DIPB to SSZ-24 and other MAPO-5 (M: Si, Mg, and Zn), and these selectivities were originated by the AFI channels. The selectivities for 4,4′-DIPB were kept 65-75% at low and moderate temperatures over MAPO-5 (M: Co and Ni); however, they were decreased by the isomerization to stable 3,4′-DIPB with the increase in temperature.
Zhang, Hui Xing,Chokkalingam, Anand,Subramaniam, Priya V.,Joseph, Stalin,Takeuchi, Seiji,Wei, Ming Deng,Al-Enizi, Abdullah M.,Jang, Hoi-Gu,Kim, Jong-Ho,Seo, Gon,Komura, Kenichi,Sugi, Yoshihiro,Vinu, Ajayan
p. 117 - 124
(2016/01/26)

Graphene Oxide Catalyzed C-H Bond Activation: The Importance of Oxygen Functional Groups for Biaryl Construction
A heterogeneous, inexpensive, and environmentally friendly graphene oxide catalytic system for the C-H bond arylation of benzene enables the formation of biaryl compounds in the presence of aryl iodides. The oxygen functional groups in these graphene oxide sheets and the addition of KOtBu are essential for the observed catalytic activity. Reactions with various model compounds and DFT calculations confirmed that these negatively charged oxygen atoms promote the overall transformation by stabilizing and activating K+ ions, which in turns facilitates the activation of the C-I bond. However, the graphene π system also greatly facilitates the overall reaction as the aromatic coupling partners are easily adsorbed.
Gao, Yongjun,Tang, Pei,Zhou, Hu,Zhang, Wei,Yang, Hanjun,Yan, Ning,Hu, Gang,Mei, Donghai,Wang, Jianguo,Ma, Ding
p. 3124 - 3128
(2016/03/12)

Iron fluoride/N-heterocyclic carbene catalyzed cross coupling between deactivated aryl chlorides and alkyl grignard reagents with or without β-hydrogens
High-yielding cross-coupling reactions of various combinations of aryl chlorides and alkyl Grignard reagents have been developed by using an iron(III) fluoride/1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene (SIPr) catalyst composite. The iron(III) fluoride/SIPr-catalyzed aryl-alkyl coupling demonstrates unprecedented scope for both aryl chlorides and alkyl Grignard reagents, thus enabling the first efficient coupling of electron-rich (deactivated) aryl chlorides with alkyl Grignard reagents without β-hydrogens. The present reaction is also effective for diverse alkyl Grignard reagents such as (trimethylsilyl)methyl, primary, and secondary alkyl Grignard reagents.
Agata, Ryosuke,Iwamoto, Takahiro,Nakagawa, Naohisa,Isozaki, Katsuhiro,Hatakeyama, Takuji,Takaya, Hikaru,Nakamura, Masaharu
p. 1733 - 1740
(2015/06/16)

Transition-metal-free arylations via photogenerated triplet 4-alkyl- and 4-trimethylsilylphenyl cations
The irradiation in protic solvents of 4-chloroalkylbenzenes and 4-chlorophenyltrimethylsilane caused the heterolytic cleavage of aryl-chlorine bonds to give the corresponding triplet phenyl cations. These were exploited for transition-metal-free arylation reactions under mild conditions to give allylbenzenes, γ-benzyl lactones, 3-arylacetals (ketals), and biaryls in moderate to good yields. The path followed was supported by DFT calculations at the UB3LYP/6-311+G(2d,p) level.
Qrareya, Hisham,Raviola, Carlotta,Protti, Stefano,Fagnoni, Maurizio,Albini, Angelo
p. 6016 - 6024
(2013/07/26)

Palladium-catalyzed arylation of simple arenes with iodonium salts
The development of an arylation protocol for simple arenes with diaryliodonium salts using the Herrmann-Beller palladacycle catalyst is reported. The reaction takes simple aromatic feedstocks and creates valuable biaryls for use in all sectors of the chem
Storr, Thomas E.,Greaney, Michael F.
supporting information
p. 1410 - 1413
(2013/05/09)

Shape-selective alkylation of biphenyl with propylene using zeolite and amorphous silica-alumina catalysts
The influence of zeolite structure for the alkylation of biphenyl with propylene was studied over various zeolites such as HY, HZSM-5, and dealuminated mordenite (DMOR), as well as amorphous SiO2/Al2O 3, in a stirred tank reactor. Biphenyl conversion was found to increase with reaction time for HZSM-5 and DMOR zeolites and reach a leveling off in 4 h, whereas for HY and amorphous SiO2/Al2O 3 a leveling off was reached within an hour. DMOR displayed the highest selectivity for 4,4′-diisopropylbiphenyl (4,4′-DIPB) even at temperatures as high as 300 °C, whereas for HY, HZSM-5 and amorphous SiO2/Al2O3 selectivities fell in the range of 10-35%; they were significantly lower than observed for DMOR. These differences in selectivity might be due to the structure and pore channels of the zeolites. DMOR was found to be an active catalyst, the selectivity for 4-isopropylbiphenyl (4-IPB) and (4,4′-DIPB) was high among isopropylbiphenyl (IPB) and diisopropylbiphenyl (DIPB) isomers, respectively, indicating DMOR possesses shape-selectivity. The selectivity of 4,4′-DIPB increased with time, while the corresponding selectivity of 4-IPB decreased for DMOR catalyst. Alkylation of biphenyl with propylene occurred with predominant formation of 4-IPB in the first step. 4-IPB is only a source in the second step of alkylation of biphenyl with propylene for the formation of 4,4′-DIPB, while 3-IPB does not participate in the formation of DIPB isomers.
Pendyala, Venkat Ramana Rao,Jacobs, Gary,Shafer, Wilson D.,Keogh, Robert A.,Kang, Jungshik,Sparks, Dennis E.,Davis, Burtron H.
p. 195 - 203
(2013/04/10)

Iron-catalyzed cross-coupling reactions of alkyl grignards with aryl sulfamates and tosylates
The iron-catalyzed cross-coupling of aryl sulfamates and tosylates has been achieved with primary and secondary alkyl Grignards. This study of iron-catalyzed cross-coupling reactions also examines the isomerization and β-hydride elimination problems that are associated with the use of isopropyl nucleophiles. While a variety of iron sources were competent in the reaction, the use of FeF3·3H2O was critical to minimize nucleophile isomerization.
Agrawal, Toolika,Cook, Silas P.
p. 96 - 99
(2013/03/28)

Isopropylation of biphenyl over ZSM-12 zeolites
ZSM-12 zeolites, ZSM-12L and ZSM-12S, with MTW topology were synthesized by using methyltriethylammonium bromide (MTEABr) and tetraethylammnoium bromide (TEABr) as structure directing agents (SDA), respectively, for the isopropylation of biphenyl (BP) usi
Chokkalingam, Anand,Kawagoe, Hiroaki,Watanabe, Seiji,Moriyama, Yasuhiro,Komura, Kenichi,Kubota, Yoshihiro,Kim, Jong-Ho,Seo, Gon,Vinu, Ajayan,Sugi, Yoshihiro
p. 23 - 30
(2013/02/23)

A cyclobutene-1,2-bis(imidazolium) salt as preligand for palladium-catalyzed cross-coupling reactions: Properties and applications
Spectroscopic investigations and the results of calculations on the title bis-imidazolium salt, its mono-and bis-carbenes, and its interactions with palladium are presented. In addition, we report on the scope and limitations of metal-catalyzed cross-coupling reactions performed with the title bis-imidazolium salt. The salt proved to be an efficient ligand precursor in room-temperature Suzuki-Miyaura reactions, C-C couplings with sterically extremely hindered biaryls,selective thiophene arylations, and couplings with vinylic chlorides. Spectroscopic investigations and the results of calculations on the title bis-imidazolium salt, its mono-and bis-carbenes, and its interactions with palladium are presented. In addition, we report on the scope and limitations of metal-catalyzed cross-coupling reactions performed with the title bis-imidazolium salt. Copyright
Rahimi, Alireza,Papai, Imre,Madarasz, Udam,Gjikaj, Mimoza,Namyslo, Jan C.,Schmidt, Andreas
scheme or table
p. 754 - 763
(2012/03/12)

Shape-selective isopropylation of aromatic hydrocarbons over h-mordenite in supercritical carbon dioxide medium
The isopropylation of aromatic hydrocarbons isobutylbenzene (IBB), naphthalene (NP), and biphenyl (BP) was examined over H-mordenite (MOR), H-β (BEA), and H-Y (FAU) zeolites in supercritical carbon dioxide (sc-CO2) medium. MOR was only selective for the formation of the least bulky 4-isobutylcumene (4-IBC) in the isopropylation of IBB. In particular, the catalytic activity and selectivity for 4-IBC were enhanced by the dealumination of MOR; MOR with 110 of SiO2/Al2O3 ratio rendered the highest performance; however, the catalytic activity was decreased by further dealumination. Thermogravimetric analyses confirmed the reduction of coke formation on the catalysts in sc-CO2 medium, preventing the deactivation of MOR. Shape-selective formation of the least bulky isomers, 2,6- diisopropylnaphthalene (2,6-DIPN) and 4,4′-diisopropylbiphenyl (4,4′-DIPB), was also observed in the isopropylation of NP and BP over MOR in sc-CO2. sc-CO2 works as an efficient medium to access and/or replace substrates and their products to/from acidic sites in the MOR channels. In particular, the removal of coke precursors from acidic sites on the zeolite is enhanced by the sc-CO2 medium, resulting in decreased coke formation.
Laha, Subhash Chandra,Naiki, Hiroaki,Komura, Kenichi,Sugi, Yoshihiro
supporting information; body text
p. 1283 - 1290
(2012/01/31)

Preparation of [Fe]-SSZ-24 through the isomorphous substitution of [B]-SSZ-24 with iron, and its catalytic properties in the isopropylation of biphenyl
[Fe]-SSZ-24, a ferrosilicate with AFI topology, was prepared through an isomorphous substitution of [B]-SSZ-24 with iron, and applied for the isopropylation of biphenyl (BP) to understand the mechanism of shape-selective catalysis. The substitution of [B]-SSZ-24 with an aqueous solution of a limited amount of Fe(NO3)3·6H2O effectively gave [Fe]-SSZ-24, and its XRD gave clear patterns of AFI topology without the peaks assigned to Fe2O3. [Fe]-SSZ-24 exhibited enhanced catalytic activity for the isopropylation of BP. Shape-selective formation of 4,4′-diisopropylbiphenyl (4,4′-DIPB) occurred at moderate temperatures (250-300 °C); however, the decreases of the selectivity for 4,4′-DIPB occurred at high temperatures (325-350 °C). On the other hand, the selectivities for 4,4′-DIPB in encapsulated products remained almost constant (ca 75%), irrespective of the reaction temperature and the SiO2/Fe2O3 ratios. The differences in the selectivities for 4,4′-DIPB between bulk and encapsulated products indicate that shape-selective formation of 4,4′-DIPB occurs in the [Fe]-SSZ-24 channels, and these channels prevent the isomerization of 4,4′-DIPB, even at 350 °C. These results suggest that the channels of SSZ-24 can discriminate 4,4′-DIPB from other possible DIPB isomers at their transition states although high reaction temperatures cause isomerization at external acid sites. Large pore molecular sieves of AFI topology, [Fe]-SSZ-24, [Al]-SSZ-24, MgAPO-5, ZnAPO-5, and SAPO-5, gave similar levels of selectivities for 4,4′-DIPB in the isopropylation of BP. These results indicate that the framework of AFI topology primarily controls shape-selective formation of 4,4′-DIPB, although catalytic activities of the materials were dependent on acidic properties.
Kawagoe, Hiroaki,Komura, Kenichi,Kim, Jong-Ho,Seo, Gon,Sugi, Yoshihiro
experimental part
p. 1 - 8
(2011/12/14)

Nickel-catalyzed cross-coupling of aryl bromides with tertiary grignard reagents utilizing donor-functionalized N-heterocyclic carbenes (NHCs)
Metal-catalyzed cross-coupling reactions are among the most important transformations in organic synthesis, allowing the efficient construction of complex structures from simpler, readily available building blocks.Many applications in large and small-scale synthesis can be found in different areas such as agrochemicals, pharmaceuticals and supramolecular chemistry. Whereas the coupling of sp2-hybridized carbon atoms in either reaction partner is well established, the use of CACHTUNGTRENUNG(sp3)-hybridized substrates presents some challenges. Catalytic cross-coupling of sterically hindered tertiary alkyl substrates is especially difficult, generally resulting in low yields, and thus, only few reports exist.[27] A big challenge in this field is not only to get the required level of reactivity, but also to overcome competing pathways like β-hydride elimination, hydrodehalogenation or isomerization
Lohre, Claudia,Droege, Thomas,Wang, Congyang,Glorius, Frank
supporting information; experimental part
p. 6052 - 6055
(2011/06/25)

Thermal transformations of 4-tert-butylbiphenyl
The thermal stability of 4-tert-butylbiphenyl was studied in the range of 703-763 K. The competition of the cracking and isomerization reactions of alkyl substituents on the aromatic ring of the reactant and its products has been revealed. The kinetic characteristics of the complex of transformations occurring in the system have been determined. Recommendations are provided regarding the conditions for the determination of the critical parameters of 4-tert-butylbiphenyl and for the processing and use of compounds with a tert-butyl moiety in the molecule.
Repkin,Nesterova,Nesterov,Golovin
experimental part
p. 149 - 153
(2011/08/05)

A versatile catalyst system for Suzuki-Miyaura syntheses of sterically hindered biaryls employing a cyclobutene-1,2-bis(imidazolium) salt
The catalyst system consisting of 3,3′-(3,4-bis(dichloro-methylene) cyclobut-1-ene-1,2-diyl)bis(1-methyl-1H-imidazolium) bis(tetrafluoroborate), Pd(OAc)2 and NaOtBu in toluene proved to be very effective for a broad variety of Suzuki-Miyaura reactions at room temperature. It is also suited for the synthesis of sterically hindered compounds including 2,6-di-tert-butyl-2′-substituted biaryls at elevated temperatures. The Royal Society of Chemistry 2010.
Schmidt, Andreas,Rahimi, Alireza
supporting information; experimental part
p. 2995 - 2997
(2010/08/05)

Organocatalysis in cross-coupling: DMEDA-catalyzed direct C-H arylation of unactivated benzene
A striking breakthrough to the frame of traditional cross-couplings/C-H functionalizations using an organocatalyst remains unprecedented. We uncovered a conceptually different approach toward the biaryl syntheses by using DMEDA as the catalyst to promote the direct C-H arylation of unactivated benzene in the presence of potassium tert-butoxide. The arylation of unactivated benzene with aryl iodides, or aryl bromides and even chlorides under the assistance of an iodo-group, could simply take place at 80 °C. The new methodology presumably involves an aryl radical anion as an intermediate. This finding offers an option toward establishing a new horizon for direct C-H/cross-coupling reactions.
Liu, Wei,Cao, Hao,Zhang, Hua,Zhang, Heng,Chung, Kin Ho,He, Chuan,Wang, Haibo,Kwong, Fuk Yee,Lei, Aiwen
supporting information; experimental part
p. 16737 - 16740
(2011/02/17)

Iron-catalyzed direct arylation of unactivated arenes with aryl halides
(Chemical Equation Presented) Iron tough: Various aryl halides were treated with unactivated arenes to form biaryl compounds in moderate to good yields. The reactions were carried out at relatively low temperature in the presence of a catalytic amount of FeCl3, with DMEDA as the ligand and LiHMDS as the base (see scheme; DMEDA=N,N'-dimethylethane-1,2-diamine, HDMS=hexamethyldisilazanide) .
Liu, Wei,Cao, Hao,Lei, Aiwen
supporting information; scheme or table
p. 2004 - 2008
(2010/06/20)

A simple and efficient hydrogenation of benzyl alcohols to methylene compounds using triethylsilane and a palladium catalyst
Hydrogenolysis of benzyl alcohols using triethylsilane (Et3SiH) and a catalytic amount of palladium(II) chloride (PdCl2) is described. The reaction takes place under mild conditions affording high yields of the corresponding methylene compounds in short reaction times.
Mirza-Aghayan, Maryam,Boukherroub, Rabah,Rahimifard, Mahshid
experimental part
p. 5930 - 5932
(2010/01/18)

Revealing a second transmetalation step in the Negishi coupling and its competition with reductive elimination: Improvement in the interpretation of the mechanism of biaryl syntheses
This paper presents an experimental and theoretical investigation of the Pd-catalyzed Negishi coupling reaction and reveals a novel second transmetalation reaction between an Ar1-Pd-Ar2 species and the organozinc reagent Ar2-ZnX. Understanding of this second step reveals how homocoupling and dehalogenation products are formed. Thus, the second transmetalation generates Ar2PdAr2 and Ar 1ZnCl, which upon reductive elimination and hydrolysis, respectively, give the homocoupling product Ar2-Ar2 and the dehalogenation product Ar1H. The ratio of the cross-coupling product Ar1-Ar2 and the homocoupling product Ar 2-Ar2 is determined by competition between the second transmetalation and reductive elimination steps. This mechanism is further supported by density functional theoretical calculations. Calculations on a series of reactions suggest a strategy in controlling the selectivity of cross-coupling and homocoupling pathways, which we have experimentally verified.
Liu, Qiang,Lan, Yu,Liu, Jing,Li, Gang,Wu, Yun-Dong,Lei, Aiwen
supporting information; experimental part
p. 10201 - 10210
(2009/12/08)

Hydrogenolysis of unstrained carbon-carbon σ bonds: Stereoselective entry into benzylic tertiary centers
(Chemical Equation Presented) The modification of sp3-hybridized carbon centers through Pd-catalyzed reductive cleavage of unstrained carbon-carbon @ bonds is described. From the hydrogenolysis of benzyl Meldrum's acids bearing an all-carbon be
Wilsily, Ashraf,Nguyen, Yen,Fillion, Eric
supporting information; experimental part
p. 15606 - 15607
(2010/01/30)

Negishi coupling of secondary alkylzinc halides with aryl bromides and chlorides
(Chemical Equation Presented) An efficient palladium-catalyzed process has been developed for Negishi coupling of secondary alkylzinc halides with a wide range of aryl bromides and activated aryl chlorides. A palladium catalyst composed of a new biaryldialkylphosphine ligand, CPhos, effectively promotes the rate of the reductive elimination step relative to the rate of the undesired β-hydride elimination. The broad substrate scope and excellent ratio of the desired secondary to the undesired primary coupling product make this method a powerful and reliable tool forC(sp3)-C(sp2) bond formation.
Han, Chong,Buchwald, Stephen L.
supporting information; experimental part
p. 7532 - 7533
(2009/10/16)

Continuous Process for preparing 4,4'-diisopropylbiphenyl
A continuous flow process has been discovered for the highly selective isopropylation of biphenyl to 4,4'-diisopropylbiphenyl. Thus biphenyl and propene in decalin are passed through a solid catalyst bed contained in a flow reactor at moderate temperature (220°C) and pressure (10-30 atm) together with a continuous stream of nitrogen. The catalyst is an acidic zeolite catalyst having a molar ratio of SiO2 to Al2O3 in a range between about 20 to 1 and about 500 to 1. Optimal catalytic performance is achieved when 35% or more of the active sites in the catalyst have an activation energy of ammonia desorption in a range between about 145 kJ/mol and about 170 kJ/mol. Additional enhancements of catalyst performance can be achieved by pretreating the acidic zeolite catalyst with a volatile basic agent prior to the alkylation reaction.
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Page/Page column 9-10

(2008/06/13)

Suzuki and Heck coupling reactions mediated by palladium complexes bearing trans-spanning diphosphines
Palladium complexes of three trans-spanning diphosphines are examined for effecting C-C coupling reactions. Ten aryl halides of varying electron density were screened in Suzuki coupling reactions with phenylboronic acid and in Heck reactions with styrene.
Smith, Rhett C.,Bodner, Christina R.,Earl, Meredith J.,Sears, Nathaniel C.,Hill, Nicholas E.,Bishop, Lee M.,Sizemore, Nicholas,Hehemann, Dave T.,Bohn, Justin J.,Protasiewicz, John D.
p. 477 - 481
(2007/10/03)

Efficient Synthesis and Resolution of trans-2-(1-Aryl-1-methylethyl)cyclohexanols; Practical Alternatives to 8-Phenylmenthol
A short synthesis and resolution of effective chiral auxiliaries of the 8-arylmenthol-type achieved using inexpensive materials, a recyclable lipase, and easily applied procedures that are amenable to large-scale preparation.A variety of isopropylarenes were α-metalated with n-butylithium/potassium tert-pentoxide and treated with cyclohexene oxide to provide racemic trans-2-(1-aryl-1-methylethyl)cyclohexanols 6a-f in fair to high yield.Candida rugosa lipase and lauric acid were used to resolve these racemic alcohols by converting the (-)-enantiomer to its laurateester.The enzymatic resolutions were carried out at 40 deg C and were faster in cyclohexane than in hexanes.The synthesis and resolution of racemic trans-2-(1-methyl-1-phenylethyl)cyclohexanol (6a) were performed on a 1 mol scale in 68 percent overall yield, requiring three steps for (+)-6a and five steps for (-)-6a.
Comins, Daniel L.,Salvador James M.
p. 4656 - 4661
(2007/10/02)

Synthesis of 4-alkyl-4-(4-methoxyphenyl)cyclohex-2-en-1-ones and 5-alkyl-5-phenyl-1,3-cyclohexadienes from bis(tricarbonylchromium)-coordinated biphenyls
(η6:η6-Biphenyl)[Cr(CO)3] 2 and (η6η64,4'-dimethoxybiphenyl) [Cr(CO)3]2 were chemically reduced with lithium anthracenide or lithium naphthalenide in THF to generate s
Rieke, Reuben D.,Schulte, Louis D.,Dawson, Bryan T.,Yang, Sheng Sbeng
p. 8388 - 8398
(2007/10/02)

TRIALKYLSILANES AS SCAVENGERS FOR THE TRIFLUOROACETIC ACID DEBLOCKING OF PROTECTING GROUPS IN PEPTIDE SYNTHESIS
Triethylsilane was used as a scavenging agent in peptide synthesis for the removal of protecting groups with TFA.The efficiency of scavenging ability was compared with anisole and ethanedithiol in a kinetic experiment.It was also found that triethylsilane/TFA reduces the indole ring of tryptophan.
Pearson, Daniel A.,Blanchette, Mary,Baker, Mary Lou,Guindon, Cathy A.
p. 2739 - 2742
(2007/10/02)

ORIENTATION IN METHYLATION AND PHENYLATION OF ALKYLBENZENES BY CATIONS GENERATED BY THE NUCLEAR CHEMICAL METHOD
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Sinotova, E. N.,Krylov, E. N.
p. 1042 - 1049
(2007/10/02)

Equilibria of isomeric transformations of alkylbiphenyls
Equilibria of mutual transformations of mono-, di-, and tri-alkylbiphenyls (ABP) were investigated in the liquid phase at 308 to 423 K.On the basis of experimental equilibrium constants, values of ΔrHm0/(kJ * mol-1) and ΔrSm0/(J * K-1 * mol-1) were calculated.Below are given correspondingly: reaction, compound and values for Et-BP (I), i-Pr-BP (II), and t-Bu-BP (III): 4-ABP = 3-ABP, I, 0.23, 5.76; II, (0.45+/-0.4), (5.72+/-1.13); III, (0.48+/-0.53), (4.83+/-0.53); 2-ABP = 4-ABP, I, -3,3, -5.76; II, -12.6, -5.76; III, -15.4, -5.76; 3,5-di-ABP = 3,3'-di-ABP, I, -0.1, 5.76; II, (0+/-0.60), (5.98+/-1.65); III, (-1.34+/-0.67), (4.48+/-1.87); 3,3'-di-ABP = 3,4'-di-ABP, I, -0.37, 0; II, (-0.64+/-1.6), (-0.48+/-4.6); III, (-0.90+/-0.39), (0+/-1.08); 4,4'-di-ABP = 4,3'-di-ABP, I, 0.24, 11.53; II, (0.47+/-0.06), (11.88+/-0.15); III, (0.35+/-2.2), (11.37+/-6.23).The joint processing of the above results gave the values of ΔrHm0/(kJ * mol-1) and ΔrSm0/(J * K-1 * mol-1) for meta-to-para-transformations of ABP: I, 0.33, 0; II, (0.59+/-0.76), (0.31+/-2.12); III, (0.71+/-1.34), (-0.37+/-3.78).
Roshchupkina, I. Yu.,Nesterova, T. N.,Rozhnov, A. M.
p. 299 - 306
(2007/10/02)