- Hydration of Alkynes Catalyzed by L-Au-X under Solvent- and Acid-Free Conditions: New Insights into an Efficient, General, and Green Methodology
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L-Au-X [L = 1,3-bis(2,6-di-isopropylphenyl)-imidazol-2-ylidene {NHCiPr}, tris(3,5-bis(trifluoromethyl)phenyl)phosphine {PArF}, bis(imino)acenaphtene-1,3-bis(2,6-di-isopropylphenyl)dihydroimidazol-2-ylidene {BIAN}, 1,3-bis(2,6-di-isopropyl-phenyl)dihydroimidazol-2-ylidene {NHCCH2}, bis(tert-butylamino)methylidene {NAC}, 2-(di-tert-butylphosphino)biphenyl {JohnPhos}, tricyclohexylphosphine {PCy3}, triphenylphosphine {PPh3}, tris(2,4-di-tert-butylphenyl)phosphite {POR3}; X- = Cl-, OTf-, OTs-] catalysts were tested in the hydration of alkynes in neat and acid-free conditions. The overall catalytic evidence confirms that not only the counterion as previously observed by us but also the ligand play a crucial role. As a matter of fact, only complexes bearing NHC ligands showed appreciable catalytic activity. A complete rationalization of the ligand and counterion effects enabled us to develop a highly efficient methodology for the hydration of inactive diphenylacetylene in solvent-, silver-, and acid-free conditions. Thus, it was possible to reduce the catalyst loading to 0.01 mol % (with respect to diphenylacetylene) leading, to the best of our knowledge, to the highest TON (3400) and TOF (435 h-1) values found at 120 °C. The favorable catalytic conditions allowed us to reach for the first time very low E-factor (0.03) and high EMY (77) values for this substrate.
- Gatto, Mattia,Del Zotto, Alessandro,Segato, Jacopo,Zuccaccia, Daniele
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- Reactivity and Crystal Structure of 10,11-Dihydro-10,11-epoxy-5H-dibenzocycloheptene. A Comparison with cis-Stilbene Oxide
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The kinetics and product distributions for the HClO4 catalysed hydrolysis of 10,11-dihydro-10,11-epoxy-5H-dibenzocycloheptene 1 and of cis-stilbene oxide 6 in tetrahydrofuran-water (8:2), have been investigated by HPLC.The former epoxide gives 9,10-dihydroanthracene-9-carbaldehyde 4 and the trans- and cis-10,11-dihydro-5H-dibenzocycloheptene-10,11-diols 2 and 3, in the ratio 6:6:1. cis-Stilbene oxide reacts with a rate constant ca. ten times lower, giving mostly (+/-)-1,2-diphenylethane-1,2-diol.These differences can be explained by the crystal structure of 1, which shows considerable ring strain due to the enlargement of the bond angles at C(10) and C(11).This structure also suggests an explanation for the much lower rate of the microsomal epoxide hydrolase catalysed hydration of 1 relative to 6.
- Bellucci, Giuseppe,Chiappe, Cinzia,Marioni, F.,Spagna, Riccardo
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- ELECTRON-TRANSFER CHAIN ISOMERIZATION OF EPOXIDES INDUCED BY ONE-ELECTRON OXIDIZING AGENTS
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One electron oxidizing agents have been employed to achieve the isomerization of epoxides to ketones.The reactions most likely proceed via a radical cation chain electron-transfer mechanism.
- Lopez, Luigi,Troisi, Luigino
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- Improving process efficiency of gold-catalyzed hydration of alkynes: Merging catalysis with membrane separation
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In this report, we investigate the integration of a membrane separation protocol in line with the gold-catalyzed hydration of alkynes. The catalytic reaction is optimised towards that end and subsequently merged with membrane technology via the development of an organic solvent nanofiltration (OSN) procedure. The protocol is investigated over both ceramic and polymeric membranes. Several gold catalysts were screened in the hydration of diphenylacetylene 1, and high rejection was observed in all cases using Borsig-type polymeric membranes. Catalyst recycling was also achieved up to 4 times using [Au(OTf)(IPr)] (3). In addition, the retained catalyst in the last catalytic cycle was analyzed and readily converted into [Au(Cl)(IPr)] (synthetic precursor to 3), using a straightforward treatment. The sustainability of the process was improved by using a green solvent, 2-methyltetrahydrofuran (Me-THF), and by reducing the amount of solvent used via the implementation of a second membrane.
- A. C. A. Bayrakdar, Tahani,Nahra, Fady,Zugazua, Oihane,Eykens, Lies,Ormerod, Dominic,Nolan, Steven P.
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- PMO-Immobilized AuI–NHC Complexes: Heterogeneous Catalysts for Sustainable Processes
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A stable periodic mesoporous organosilica (PMO) with accessible sulfonic acid functionalities is prepared via a one-pot-synthesis and is used as solid support for highly active catalysts, consisting of gold(I)-N-heterocyclic carbene (NHC) complexes. The gold complexes are successfully immobilized on the nanoporous hybrid material via a straightforward acid–base reaction with the corresponding [Au(OH)(NHC)] synthon. This catalyst design strategy results in a boomerang-type catalyst, allowing the active species to detach from the surface to perform the catalysis and then to recombine with the solid after all the starting material is consumed. This boomerang behavior is assessed in the hydration of alkynes. The tested catalysts were found to be active in the latter reaction, and after an acidic work-up, the IPr*-based gold catalyst can be recovered and then reused several times without any loss in efficiency.
- De Canck, Els,Nahra, Fady,Bevernaege, Kevin,Vanden Broeck, Sofie,Ouwehand, Judith,Maes, Diederick,Nolan, Steven P.,Van Der Voort, Pascal
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- Investigation of axial ligand effects on catalytic activity of manganese porphyrin, evidence for the importance of hydrogen bonding in cytochrome-P450 model reactions
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Various nitrogenous bases, such as imidazoles, pyridines and amines were employed as axial ligands in epoxidation reaction of cyclooctene bytetra-n-butylammonium hydrogen monopersulfate (n-Bu4NHSO5), in the presence of Mn(III)-tetrakis(2,3-dimethoxyphenyl)porphyrin-acetate (T(2,3-OMeP)PorMnOAc). T(2,3-OMeP)PorMnOAc is a fairly stable catalyst, with the ability of producing hydrogen bonding. High epoxidation yield of 85 ± 6% was obtained in the presence of imidazole axial ligand with 100% selectivity in 30 min. Higher conversion of around 100% was obtained by pyridine axial base, while selectivity was reduced to 69%. Further epoxidation reactions were also performed using Mn(III)-Tetrakis(2,3-dihydroxyphenyl)porphyrin-acetate (T(2,3-OHP)PorMnOAc) as catalyst. In addition to the usual electronic and steric effects, it is proposed that the catalytic activity depends on the existence and kind of hydrogen bonding between the axial base and the ortho-methoxy or hydroxy groups on the phenyl rings of manganese porphyrin. The cis to trans ratio of cis-stilbene oxide formed by imidazole and pyridine axial bases were obtained as 7.5 and 2.5 respectively. In addition GC-Ms and UV-vis studies were employed to find the nature of active species and product formation. Our DFT calculations disclosed that pyridine hydrogen bonding with moiety of the macrocycle rings strongly affects the relative energies of S/Q spin states in [T(2,3-OMeP)PorMnV(O)(Py)]+, in that it results in the longer Mn-O bond and reactivity toward substrates.
- Mesbahi, Elnaz,Safari, Nasser,Gheidi, Mahin
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- ABOUT THE MECHANISM OF THE PHOTOLYSIS OF BENZOYLTRIETHYLGERMANE, Et3GeCOPh
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The detailed mechanism of the photolysis of benzoyltriethylgerman Et3GeCOPh in various media has been studied using the chemically induced dynamic nuclear polarization method (1 H CIDNP).It has been shown that in all cases the photolytic decomposition lea
- Taraban, M. B.,Maryasova, V. I.,Leshina, T. V.,Rybin, L. I.,Gendin, D. V.,Vyazankin, N. S.
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- Synthesis, reactivity and catalytic activity of Au-PAd3complexes
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Tri(1-adamantyl)phosphine (PAd3) possesses unique steric and electronic properties positioning it at the border between tertiary phosphines and N-heterocyclic carbenes (NHC). Novel Au-PAd3complexes were synthesized from the known [Au(PAd3)Cl]. We have optimised reaction conditions for the synthesis of this useful synthon in order to circumvent the formation of the [Au(PAd3)2]Cl. [Au(PAd3)Cl] was used to access a number of derivatives and some were deployed as catalysts. The hydration of alkynes was targeted to gauge the reactivity of Au-PAd3complexes and permit comparison with NHC and tertiary phosphine congeners.
- Voloshkin, Vladislav A.,Saab, Marina,Van Hecke, Kristof,Lau, Sii Hong,Carrow, Bradley P.,Nolan, Steven P.
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- Synthesis and characterization of gold(I) complexes of dibenzotropylidene-functionalized NHC ligands (Trop-NHCs)
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Gold(I) complexes of dibenzotropylidene-functionalized N-heterocyclic carbene ligands (Trop-NHCs) have been prepared in order to investigate their structural features and to reveal possible interactions of the olefin unit with the metal center. The precursor imidazolium chloride salts (R-1) were generated in a single step using N-substituted imidazoles (R = H, Me, DiPP, Ad) and 1 or 2 equiv of Trop-Cl, generating unsymmetrical and symmetrical NHC-olefin hybrids. The structural parameters of the ligands were determined by synthesis and X-ray diffraction analysis of their corresponding gold(I) chloride complexes, revealing highly flexible steric demands of the Trop unit. Conversion of these complexes with halide-abstracting reagents such as AgNTf2 and NaBArF24 cleanly gave neutral, NTf2-coordinated complexes of the type [(NHC)Au(NTf2)] (R-3) and the cationic bis-NHC-coordinated complexes [(NHC)2Au]BArF24 (R-4), respectively. The Gagosz-type complexes R-3 were further tested in the hydration of diphenylacetylene, showing a clear trend in activity depending on the ligand's sensitivity to hydrolysis.
- Brill, Marcel,Collado, Alba,Cordes, David B.,Slawin, Alexandra M. Z.,Vogt, Matthias,Grützmacher, Hansj?rg,Nolan, Steven P.
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- Chiral α-hydroxy acid-coadsorbed TiO2 photocatalysts for asymmetric induction in hydrogenation of aromatic ketones
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Modification of titanium dioxide (TiO2) photocatalysts with chiral reagents was evaluated by the hydrogenation of aromatic ketones. The strong adsorption of chiral mandelic acid (R)-MA on TiO2 was confirmed by comparing the inhibitio
- Kohtani, Shigeru,Kawashima, Akira,Masuda, Fumie,Sumi, Momono,Kitagawa, Yuichi,Yoshioka, Eito,Hasegawa, Yasuchika,Miyabe, Hideto
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- Carbenoids by Deoxygenation of Carbonyl Compounds with Chloromethylsilanes
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Deoxygenation of benzophenone, benzaldehyde, and cyclohexanone with chloromethylsilanes and zinc-copper couple in ether is reported to yield 2,2,2-triphenylacetophenone, a mixture of deoxybenzoin and diphenylacetaldehyde, and a bicyclic ketone with the proposed 2-oxocycloheptanespirocyclohexane structure, respectively; a carbene mechanism is proposed.
- Smith, Clifford L.,Arnett, James,Ezike, James
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- A structureeactivity relationship study on the Wacker oxidation of stilbenes at ambient condition
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To evaluate which structural elements of the stilbenes are responsible for their activity on the Wacker oxidation, a series of stilbenes with various functional moieties and substitution patterns were considered. In this regard, it is found that the oxidation rate of stilbenes strongly depends on their structures to give the corresponding carbonyl compounds. Consequently, the ortho position of alkene and methoxy groups plays a key role in the complexation with PdCl2. The oxidation process is clean with high selectivity of product and low percentage of byproducts.
- Darabi, Hossein Reza,Mirzakhani, Mohsen,Aghapoor, Kioumars,Jadidi, Khosrow,Faraji, Laleh,Sakhaee, Nader
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- Reusable functionalized polysiloxane-supported palladium catalyst for Suzuki–Miyaura cross-coupling
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Palladium catalyst, obtained in the reaction of PdCl2(cod) with poly[(3-N-midazolopropyl)methylsiloxane-co-bisdimethylsiloxane], was used in the Suzuki–Miyaura cross-coupling of aryl bromides with phenylboronic acid. Catalytic reactions, performed at 40–80 °C in water or 2-propanol/water mixture, led to high yields of 2-methylbiphenyl with TOF up to 25,000 h?1. In recycling experiments, excellent results were obtained in eight subsequent runs. With application of microwave heating, more than 95% of product was formed under mild conditions and short time. XRD, TEM, and XPS methods evidenced the presence of Pd(0) nanoparticles bonded to the polysiloxane support. Their important role in the catalytic process was indicated by the results of mercury poisoning test.
- Borkowski,Zawartka,Pospiech,Mizerska,Trzeciak,Cypryk,Tylus
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- Electrochemical oxidation-induced benzyl C–H carbonylation for the synthesis of aromatic α-diketones
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Electrochemical oxidation-induced direct carbonylation of benzyl C–H bond for the synthesis of aromatic α-diketones is described. In this process, tetrabutylammonium iodide (nBu4NI) not only acts as an electrolyte, but its iodine anion is oxidized to an iodine radical at the anode, acting as a hydrogen atom transfer agent. The iodine radical extracts the benzyl hydrogen atom and causes the carbonylation of the benzyl position, where O2 in the air is used as an oxygen source.
- Tan, Yu-Fang,Chen, Yuan,Li, Rui-Xue,Guan, Zhi,He, Yan-Hong
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supporting information
(2021/12/21)
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- Benzylic Aroylation of Toluenes Mediated by a LiN(SiMe3)2/Cs+System
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Chemoselective deprotonative functionalization of benzylic C-H bonds is challenging, because the arene ring contains multiple aromatic C(sp2)-H bonds, which can be competitively deprotonated and lead to selectivity issues. Recently it was found that bimetallic [MN(SiMe3)2 M = Li, Na]/Cs+ combinations exhibit excellent benzylic selectivity. Herein, is reported the first deprotonative addition of toluenes to Weinreb amides mediated by LiN(SiMe3)2/CsF for the synthesis of a diverse array of 2-arylacetophenones. Surprisingly, simple methyl benzoates also react with toluenes under similar conditions to form 2-arylacetophenones without double addition to give tertiary alcohol products. This finding greatly increases the practicality and impact of this chemistry. Some challenging substrates with respect to benzylic deprotonations, such as fluoro and methoxy substituted toluenes, are selectively transformed to 2-aryl acetophenones. The value of benzylic deprotonation of 3-fluorotoluene is demonstrated by the synthesis of a key intermediate in the preparation of Polmacoxib.
- Gu, Yuanyun,Zhang, Zhen,Wang, Yan-En,Dai, Ziteng,Yuan, Yaqi,Xiong, Dan,Li, Jie,Walsh, Patrick J.,Mao, Jianyou
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supporting information
p. 406 - 418
(2022/01/14)
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- H2O2-mediated room temperature synthesis of 2-arylacetophenones from arylhydrazines and vinyl azides in water
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An environmentally benign, cost-efficient and practical methodology for the room temperature synthesis of 2-arylacetophenones in water has been discovered. The facile and efficient transformation involves the oxidative radical addition of arylhydrazines with α-aryl vinyl azides in the presence of H2O2 (as a radical initiator) and PEG-800 (as a phase-transfer catalyst). From the viewpoint of green chemistry and organic synthesis, the present protocol is of great significance because of using cheap, non-toxic and readily available starting materials and reagents as well as amenability to gram-scale synthesis, which provides an attractive strategy to access 2-arylacetophenones.
- Luo, Mengqiang,Zhang, Yaohong,Fang, Ping,Li, Yan,Qi, Chenze,Li, Yong,Shen, Runpu,Cheng, Kai,Wang, Hai
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supporting information
p. 630 - 635
(2022/02/01)
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- Bis-Rhodamines Bridged with a Diazoketone Linker: Synthesis, Structure, and Photolysis
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Two fluorophores bound with a short photoreactive bridge are fascinating structures and remained unexplored. To investigate the synthesis and photolysis of such dyes, we linked two rhodamine dyes via a diazoketone bridge (?COCN2?) attached to p
- Belov, Vladimir N.,Bossi, Mariano L.,Hell, Stefan W.,Shojaei, Heydar
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- Nonheme manganese(III) complexes for various olefin epoxidation: Synthesis, characterization and catalytic activity
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Three mononuclear imine-based non-heme manganese(III) complexes with tetradentate ligands which have two deprotonated phenolate moieties, ([(X2saloph)Mn(OAc)(H2O)], 1a for X = Cl, 1b for X = H, and 1c for X = CH3, saloph = N,N-o-phenylenebis(salicylidenaminato)), were synthesized and characterized by 1H NMR, 13C NMR, ESI-Mass and elemental analysis. MnIII complexes catalysed efficiently various olefin epoxidation reactions with meta-chloroperbenzoic acid (MCPBA) under the mild condition. MnIII complexes 1a and 1c with the electron-withdrawing group -Cl and electron-donating group –CH3 showed little substituent effect on the epoxidation reactions. Product analysis, Hammett study and competition experiments with cis- and trans-2-octene suggested that MnIV = O, MnV = O, and MnIII-OOC(O)R species might be key oxidants in the epoxidation reaction under this catalytic system. In addition, the use of PPAA as a mechanistic probe demonstrated that Mn-acylperoxo intermediate (MnIII-OOC(O)R) 2 generated from the reaction of peracid with manganese complexes underwent both the heterolysis and the homolysis to produce MnV = O (3) or MnIV = O species (4). Moreover, the MnIII-OOC(O)R 2 species could react directly with the easy-to-oxidize substrate to give epoxide, whereas the species 2 might not be competent to the difficult-to-oxidize substrate for the epoxidation reaction.
- Lee, Sojeong,Park, Soyoung,Lee, Myoung Mi,Lee, Jiyoung,Kim, Cheal
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- Pd nanoparticles supported on pyrazolone-functionalized hollow mesoporous silica as an excellent heterogeneous nanocatalyst for the selective oxidation of benzyl alcohol
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Hollow mesoporous silica nanoparticles (HMSNs), by exploiting both their organo-functionalized surface and porous shell were chosen as the ideal support for the immobilization of palladium nanoparticles (Pd-NPs). The HMSNs were created by acidic removal of Fe3O4 nanoparticles from silica-coated Fe3O4 core-shell. The catalyst was prepared following surface modification of HMSNs by (3-chloropropyl)-triethoxysilane (CPTES), functionalization by pyrazolone-based ligand, and stabilization of Pd-NPs on HMSNs. The resulting catalyst was fully characterized by different analytical techniques. This new heterogeneous catalyst showed high catalytic activity and excellent selectivity in the selective oxidation of benzyl alcohols in ethanol at ambient temperature. Easy separation by centrifuge and reusability for five successive cycles without significant loss of catalytic activity were some advantages of this catalyst.
- Ghorbani, Somayeh,Parnian, Rouhallah,Soleimani, Ebrahim
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- Asymmetric Catalytic Epoxidation of Terminal Enones for the Synthesis of Triazole Antifungal Agents
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An enantioselective epoxidation of α-substituted vinyl ketones was realized to construct the key epoxide intermediates for the synthesis of various triazole antifungal agents. The reaction proceeded efficiently in high yields with good enantioselectivities by employing a chiral N,N′-dioxide/ScIII complex as the chiral catalyst and 35% aq. H2O2 as the oxidant. It enabled the facile transformation for optically active isavuconazole, efinaconazole, and other potential antifungal agents.
- Feng, Xiaoming,He, Qianwen,Liu, Xiaohua,Zhang, Dong,Zhang, Fengcai
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supporting information
p. 6961 - 6966
(2021/09/11)
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- Z-Scheme nanocomposite with high redox ability for efficient cleavage of lignin C-C bonds under simulated solar light
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Depolymerization of lignin, a key component of lignocellulose, is a sustainable approach to provide value-added aromatics. Selective cleavage of recalcitrant C-C linkages is a key challenge for lignin depolymerization. Photocatalysis, which can provide highly reactive species under mild conditions, represents a potential strategy for such C-C bond cleavage. Here, we report an efficient approach to break lignin C-C bonds using a Z-scheme Ag3PO4-polymeric carbon nitride (PCN) nanocomposite under simulated solar light at room temperature. Various lignin model compounds were converted into aromatic aldehydes with high yields of 66%-95%. Our mechanistic study reveals that the C-C bond cleavage mainly involves an electron-hole coupled photoredox mechanism. The construction of a Z-scheme Ag3PO4-PCN heterojunction structure is essential to simultaneously preserve the strong reduction and oxidation capability of its components, which is key for the electron-hole coupled Cα-Cβ bond cleavage. The present work offers useful guidance for the design of efficient semiconductors for C-C bond cleavage through band structure engineering. This journal is
- Lin, Jinchi,Sels, Bert F.,Wang, Ye,Wu, Xuejiao,Xie, Shunji,Zhang, Huizhen,Zhang, Qinghong
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p. 10071 - 10078
(2021/12/24)
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- Para -Selective hydroxylation of alkyl aryl ethers
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para-Selective hydroxylation of alkyl aryl ethers is established, which proceeds with a ruthenium(ii) catalyst, hypervalent iodine(iii) and trifluoroacetic anhydride via a radical mechanism. This protocol tolerates a wide scope of substrates and provides a facile and efficient method for preparing clinical drugs monobenzone and pramocaine on a gram scale.
- Zhu, Runqing,Sun, Qianqian,Li, Jing,Li, Luohao,Gao, Qinghe,Wang, Yakun,Fang, Lizhen
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supporting information
p. 13190 - 13193
(2021/12/16)
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- Site-Specific Oxidation of (sp3)C-C(sp3)/H Bonds by NaNO2/HCl
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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
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p. 4057 - 4061
(2021/05/26)
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- HCl-Catalyzed Aerobic Oxidation of Alkylarenes to Carbonyls
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The construction of C?O bonds through C?H bond functionalization remains fundamentally challenging. Here, a practical chlorine radical-mediated aerobic oxidation of alkylarenes to carbonyls was developed. This protocol employed commercially available HCl as a hydrogen atom transfer (HAT) reagent and air as a sustainable oxidant. In addition, this process exhibited excellent functional group tolerance and a broad substrate scope without the requirement for external metal and oxidants. The mechanistic hypothesis was supported by radical trapping, 18O labeling, and control experiments.
- Ding, Ling,Liu, Yuxiu,Niu, Kaikai,Shi, Xiaodi,Song, Hongjian,Wang, Qingmin
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- Selective Electrochemical Oxygenation of Alkylarenes to Carbonyls
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An efficient electrochemical method for benzylic C(sp3)-H bond oxidation has been developed. A variety of methylarenes, methylheteroarenes, and benzylic (hetero)methylenes could be converted into the desired aryl aldehydes and aryl ketones in moderate to excellent yields in an undivided cell, using O2 as the oxygen source and lutidinium perchlorate as an electrolyte. On the basis of cyclic voltammetry studies, 18O labeling experiments, and radical trapping experiments, a possible single-electron transfer mechanism has been proposed for the electrooxidation reaction.
- Li, Xue,Bai, Fang,Liu, Chaogan,Ma, Xiaowei,Gu, Chengzhi,Dai, Bin
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supporting information
p. 7445 - 7449
(2021/10/02)
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- Selective electrochemical oxidation of aromatic hydrocarbons and preparation of mono/multi-carbonyl compounds
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A selective electrochemical oxidation was developed under mild condition. Various mono-carbonyl and multi-carbonyl compounds can be prepared from different aromatic hydrocarbons with moderate to excellent yield and selectivity by virtue of this electrochemical oxidation. The produced carbonyl compounds can be further transformed into α-ketoamides, homoallylic alcohols and oximes in a one-pot reaction. In particular, a series of α-ketoamides were prepared in a one-pot continuous electrolysis. Mechanistic studies showed that 2,2,2-trifluoroethan-1-ol (TFE) can interact with catalyst species and generate the corresponding hydrogen-bonding complex to enhance the electrochemical oxidation performance. [Figure not available: see fulltext.]
- Li, Zhibin,Zhang, Yan,Li, Kuiliang,Zhou, Zhenghong,Zha, Zhenggen,Wang, Zhiyong
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p. 2134 - 2141
(2021/09/29)
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- Copper-Catalyzed Three-Component Carboboronation of Allenes Using Highly Strained Cyclic Ketimines as Electrophiles
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A diastereoselective copper and NHC-ligand-catalyzed three-component difunctionalization of allenes with bis(pinacolato)diboron and 2H-azirines to afford borylated allylaziridines is described. The reaction exhibits complete diastereoselectivity and good yields, and the further chlorination of the corresponding borylated products was also performed. It is believed that the high ring-strain force of 2H-azirines facilitates the reaction. More chemical transformations of borylated allylaziridines are also reported.
- Deng, Hao,Dong, Yujie,Shangguan, Yu,Yang, Fazhou,Han, Sheng,Wu, Jiaqi,Liang, Bo,Guo, Hongchao,Zhang, Cheng
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supporting information
p. 4431 - 4435
(2021/05/26)
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- One-pot synthesis of α,β-unsaturated ketones through sequential alkyne dimerization/hydration reactions using the Hoveyda-Grubbs catalyst
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Herein we report a sequential one-pot alkyne dimerization/hydration protocol for the regioselective synthesis of α,β-unsaturated ketones in quantitative yields. The alkyne dimerization reactions of terminal arylacetylenes proceeded with high regioselectivity in the presence of the Hoveyda-Grubbs 2nd generation catalyst (1 mol%) and tricyclohexylphosphine (4 mol%). The hydration reactions ofin situformed 1-aryl-3-en-1-ynes proceeded very rapidly in the presence of CCl3COOH/p-TsOH·H2O, yielding the corresponding unsaturated ketones within 15 minutes in quantitative yields. Different arylacetylene derivatives were converted to the corresponding α,β-unsaturated ketones in quantitative yields (94-95%) using sequential one-pot alkyne dimerization/hydration reactions.
- ?ztürk, Bengi ?zgün,?ehito?lu, Solmaz Karabulut,A?kun, Mina,Sar?aslan, Begüm,Tunal?, Zeynep
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supporting information
p. 16689 - 16695
(2021/09/27)
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- Breaking the Trend: Insight into Unforeseen Reactivity of Alkynes in Cobalt-Catalyzed Weak Chelation-Assisted Regioselective C(4)-H Functionalization of 3-Pivaloyl Indole
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Unique reactivity of diphenylacetylene has been uncovered through weak chelation-assisted cobalt-catalyzed regioselective C(4)-H activation of 3-pivolyl indole. α-Hydroxy ketone and α,β-unsaturated ketone derivatives have been synthesized in good yields from indole and alkynes. Notably, the indole C(4)-H-functionalized α,β-unsaturated ketone product was obtained with high stereo- and regioselectivity simply by changing the coupling partner from symmetrical alkynes to unsymmetrical aromatic-aliphatic alkynes. Most importantly, trifluoroethanol acts as a sole source of water for this conversion. Quantitative detection of bis(2,2,2-trifluoroethyl) ether from dry trifluoroethanol through 19F NMR and LCMS studies indirectly confirms the in situ formation of water. A six-membered cobaltacycle intermediate was detected in HRMS, and also, this was further confirmed by the quantum mechanical calculations, which accounts for the highly regioselective C(4)-H functionalization.
- Adhikari, Gopal Krushna Das,Banjare, Shyam Kumar,Dutta, Juhi,Nanda, Tanmayee,Pati, Bedadyuti Vedvyas,Ravikumar, Ponneri C.
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p. 11579 - 11587
(2021/09/22)
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- Rhodium-Catalyzed Aerobic Decomposition of 1,3-Diaryl-2-diazo-1,3-diketones: Mechanistic Investigation and Application to the Synthesis of Benzils
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The conversion of 1,3-diaryl-2-diazo-1,3-diketones to 1,2-daryl-1,2-diketones (benzils) is reported based on a rhodium(II)-catalyzed aerobic decomposition process. The reaction occurs at ambient temperatures and can be catalyzed by a few dirhodium carboxylates (5 mol %) under a balloon pressure of oxygen. Moreover, an oxygen atom from the O2 reagent is shown to be incorporated into the product, and this is accompanied by the extrusion of a carbonyl unit from the starting materials. Mechanistically, it is proposed that the decomposition may proceed via the interaction of a ketene intermediate resulting from a Wolff rearrangement of the carbenoid, with a rhodium peroxide or peroxy radical species generated upon the activation of molecular oxygen. The proposed mechanism has been supported by the results from a set of controlled experiments. By using this newly developed strategy, a large array of benzil derivatives as well as 9,10-phenanthrenequinone were synthesized from the corresponding diazo substrates in varying yields. On the other hand, the method did not allow the generation of benzocyclobutene-1,2-dione from 2-diazo-1,3-indandione because of the difficulty of inducing the initial rearrangement.
- Zhu, Jia-Liang,Tsai, Yi-Ting
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p. 813 - 828
(2020/12/22)
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- Palladium-catalyzed synthesis of α-aryl acetophenones from styryl ethers and aryl diazonium saltsviaregioselective Heck arylation at room temperature
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Preparation of α-aryl acetophenones from styryl ethers and aryldiazonium salts is described. The reaction is catalyzed by palladium acetate at room temperature in the absence of ligand and base. The developed method is highly attractive in terms of reaction conditions, substrate scope, functional group tolerance and yields. Synthetic applications of the present method are demonstrated by preparing α-aryl indoles and 3-aryl isocoumarin from styryl ethers.
- Kandasamy, Jeyakumar,Lee, Yong Rok,Singh, Adesh Kumar,Venkatesh, Rapelly
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p. 7832 - 7837
(2021/09/28)
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- Combined Theoretical and Experimental Studies Unravel Multiple Pathways to Convergent Asymmetric Hydrogenation of Enamides
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We present a highly efficient convergent asymmetric hydrogenation of E/Z mixtures of enamides catalyzed by N,P-iridium complexes supported by mechanistic studies. It was found that reduction of the olefinic isomers (E and Z geometries) produces chiral amides with the same absolute configuration (enantioconvergent hydrogenation). This allowed the hydrogenation of a wide range of E/Z mixtures of trisubstituted enamides with excellent enantioselectivity (up to 99% ee). A detailed mechanistic study using deuterium labeling and kinetic experiments revealed two different pathways for the observed enantioconvergence. For α-aryl enamides, fast isomerization of the double bond takes place, and the overall process results in kinetic resolution of the two isomers. For α-alkyl enamides, no double bond isomerization is detected, and competition experiments suggested that substrate chelation is responsible for the enantioconvergent stereochemical outcome. DFT calculations were performed to predict the correct absolute configuration of the products and strengthen the proposed mechanism of the iridium-catalyzed isomerization pathway.
- Yang, Jianping,Massaro, Luca,Krajangsri, Suppachai,Singh, Thishana,Su, Hao,Silvi, Emanuele,Ponra, Sudipta,Eriksson, Lars,Ahlquist, M?rten S. G.,Andersson, Pher G.
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supporting information
p. 21594 - 21603
(2021/12/27)
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- Cobalt-Catalyzed Aerobic Oxidative Cleavage of Alkyl Aldehydes: Synthesis of Ketones, Esters, Amides, and α-Ketoamides
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A widely applicable approach was developed to synthesize ketones, esters, amides via the oxidative C?C bond cleavage of readily available alkyl aldehydes. Green and abundant molecular oxygen (O2) was used as the oxidant, and base metals (cobalt and copper) were used as the catalysts. This strategy can be extended to the one-pot synthesis of ketones from primary alcohols and α-ketoamides from aldehydes.
- Li, Tingting,Hammond, Gerald B.,Xu, Bo
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p. 9737 - 9741
(2021/05/31)
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- Versatile and base-free copper-catalyzed α-arylations of aromatic ketones using diaryliodonium salts
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A ligand and base-free copper catalyzed synthetic method for the efficient α-arylation of aromatic ketones is described. In order to avoid strong bases, ketone-derived silyl enol ethers were employed. Their reaction with diaryliodonium salts as aryl source provided the intermolecular C–C coupling displaying good functional group tolerance and requiring low catalyst loading.
- Bouquin, Maxime,Jaroschik, Florian,Taillefer, Marc
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- Iron-Catalyzed Enantioselective Radical Carboazidation and Diazidation of α,β-Unsaturated Carbonyl Compounds
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Azidation of alkenes is an efficient protocol to synthesize organic azides which are important structural motifs in organic synthesis. Enantioselective radical azidation, as a useful strategy to install a C-N3 bond, remains challenging due to the inherently instability and unique structure of radicals. Here, we disclose an efficient enantioselective radical carboazidation and diazidation of α,β-unsaturated ketones and amides catalyzed by chiral N,N′-dioxide/Fe(OTf)2 complexes. An array of substituted alkenes was transformed to the corresponding α-azido carbonyl derivatives in good to excellent enantioselectivities, benefiting the preparation of chiral α-amino ketones, vicinal amino alcohols, and vicinal diamines. Control experiments and mechanistic studies proved the radical pathway in the reaction process. The DFT calculations showed that the azido transferred to the radical intermediate via an intramolecular five-membered transition state with the internal nitrogen of the Fe-N3 species.
- Dong, Shunxi,Feng, Xiaoming,He, Jun,Liu, Wen,Liu, Xiaohua,Pu, Maoping,Wu, Yun-Dong,Zhang, Tinghui
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p. 11856 - 11863
(2021/08/16)
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- Ferric ion concentration-controlled aerobic photo-oxidation of benzylic C–H bond with high selectivity and conversion
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A Fe(III)-promoted highly selective photo-oxidation of benzylic C–H bond delivering relative carbonyl products is reported. By altering the concentration of ferric salt, methylarenes can be selectively oxidized under UV irradiation to furnish aromatic aldehydes or acids, respectively. By this protocol, the oxidation of ethylarenes provides the corresponding acetophenones. The reaction is inferred to involve divergent pathways in different concentrations of catalyst for the alternative selectivity between aldehydes and aicds. The reusable catalyst, high conversion and selectivity make this oxidation a green and economic protocol for the synthesis of aromatic carbonyl compounds.
- Bu, Hongzhong,Gu, Jiefan,Li, Yufeng,Ma, Hongfei,Wan, Yuting,Wu, Zheng-Guang,Zhang, Weijian,Zhou, Ying'ao,Zhu, Hongjun
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- Catalytic, Kinetic, and Mechanistic Insights into the Fixation of CO2 with Epoxides Catalyzed by Phenol-Functionalized Phosphonium Salts
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A series of hydroxy-functionalized phosphonium salts were studied as bifunctional catalysts for the conversion of CO2 with epoxides under mild and solvent-free conditions. The reaction in the presence of a phenol-based phosphonium iodide proceeded via a first order rection kinetic with respect to the substrate. Notably, in contrast to the aliphatic analogue, the phenol-based catalyst showed no product inhibition. The temperature dependence of the reaction rate was investigated, and the activation energy for the model reaction was determined from an Arrhenius-plot (Ea=39.6 kJ mol?1). The substrate scope was also evaluated. Under the optimized reaction conditions, 20 terminal epoxides were converted at room temperature to the corresponding cyclic carbonates, which were isolated in yields up to 99 %. The reaction is easily scalable and was performed on a scale up to 50 g substrate. Moreover, this method was applied in the synthesis of the antitussive agent dropropizine starting from epichlorohydrin and phenylpiperazine. Furthermore, DFT calculations were performed to rationalize the mechanism and the high efficiency of the phenol-based phosphonium iodide catalyst. The calculation confirmed the activation of the epoxide via hydrogen bonding for the iodide salt, which facilitates the ring-opening step. Notably, the effective Gibbs energy barrier regarding this step is 97 kJ mol?1 for the bromide and 72 kJ mol?1 for the iodide salt, which explains the difference in activity.
- Hu, Yuya,Wei, Zhihong,Frey, Anna,Kubis, Christoph,Ren, Chang-Yue,Spannenberg, Anke,Jiao, Haijun,Werner, Thomas
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p. 363 - 372
(2020/11/30)
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- C-H Alkylation of Aldehydes by Merging TBADT Hydrogen Atom Transfer with Nickel Catalysis
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Catalyst controlled site-selective C-H functionalization is a challenging but powerful tool in organic synthesis. Polarity-matched and sterically controlled hydrogen atom transfer (HAT) provides an excellent opportunity for site-selective functionalization. As such, the dual Ni/photoredox system was successfully employed to generate acyl radicals from aldehydes via selective formyl C-H activation and subsequently cross-coupled to generate ketones, a ubiquitous structural motif present in the vast majority of natural and bioactive molecules. However, only a handful of examples that are constrained to the use of aryl halides are developed. Given the wide availability of amines, we developed a cross-coupling reaction via C-N bond cleavage using the economic nickel and TBADT catalyst for the first time. A range of alkyl and aryl aldehydes were cross-coupled with benzylic and allylic pyridinium salts to afford ketones with a broad spectrum of functional group tolerance. High regioselectivity toward formyl C-H bonds even in the presence of α-methylene carbonyl or α-amino/oxy methylene was obtained.
- Murugesan, Vetrivelan,Ganguly, Anirban,Karthika, Ardra,Rasappan, Ramesh
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p. 5389 - 5393
(2021/07/21)
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- Chemoselective reduction of ?,￠-unsaturated carbonyl and carboxylic compounds by hydrogen iodide
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The selective reduction of ?,￠-unsaturated carbonyl compounds was achieved to produce saturated carbonyl compounds with aqueous HI solution. The introduction of an aryl group at an ? or ￠ position efficiently facilitated the reduction with good yield. The reaction was applicable to compounds bearing carboxylic acids and halogen atoms. Through the investigation of the reaction mechanism, it was found that Michael-type addition of iodide occurred to produce ￠-iodo compounds followed by the reduction of C-I bond via anionic and radical paths.
- Matsumoto, Shoji,Marumoto, Hayato,Akazome, Motohiro,Otani, Yasuhiko,Kaiho, Tatsuo
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p. 590 - 599
(2021/03/29)
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- Regioselective Synthesis of α-Functional Stilbenes via Precise Control of Rapid cis- trans Isomerization in Flow
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The rapid cis-trans isomerization of α-anionic stilbene was regioselectively controlled by using flow microreactors, and its reaction with various electrophiles was conducted. The reaction time was precisely controlled within milliseconds to seconds at -50 °C to selectively give the cis- or trans-isomer in high yields. This synthetic method in flow was well-applied to synthesize precursors of commercial drug compound, (E)- and (Z)-tamoxifen with high regioselectivity and productivity.
- Lee, Hyune-Jea,Yonekura, Yuya,Kim, Nayoung,Yoshida, Jun-Ichi,Kim, Heejin
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supporting information
p. 2904 - 2910
(2021/05/05)
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- Benzylic aroylation of toluenes with unactivated tertiary benzamides promoted by directed ortho-lithiation
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The deprotonative functionalization of toluenes, for their weak acidity, generally needs strong bases, thus leading to the requirement of harsh conditions and the generation of by-products. Direct nucleophilic acyl substitution reaction of amides with organometallic reagents could provide an ideal solution for ketone synthesis. However, the inert amides and highly reactive organometallic reagents bring great challenges for an efficient and selective synthetic approach. Herein, we reported an lithium diisopropylamide (LDA)-promoted benzylic aroylation of toluenes with unactivated tertiary benzamides, providing a direct and efficient synthesis of various aryl benzyl ketones. This process features a kinetic deprotonative functionalization of toluenes with a readily available base LDA. Mechanism studies revealed that the directed ortho-lithiation of the tertiary benzamide with LDA promoted the benzylic kinetic deprotonation of toluene and triggered the nucleophilic acyl substitution reaction with the amide. [Figure not available: see fulltext.].
- Bao, Can-Can,Luo, Yan-Long,Du, Hui-Zhen,Guan, Bing-Tao
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p. 1349 - 1354
(2021/07/12)
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- Ruthenium(II)-Catalyzed Cross-Coupling of Benzoyl Formic Acids with Toluenes: Synthesis of 2-Phenylacetophenones
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Herein, we report a direct method to synthesize 2-phenylacetophenone through a ruthenium(II)-catalyzed cross-coupling reaction between acyl and benzyl radical. The various derivatives of 2-phenylacetophenone were prepared easily in moderate to good yields. These reactions provide a straightforward pathway to synthesize a variety of ketones bearing various functional groups.
- Chen, Yujie,Dai, Chenyang,Huang, Zhibin,Jiang, Yaqiqi,Shu, Sai,Yang, Shan,Zhao, Yingsheng
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p. 2955 - 2961
(2021/07/22)
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- Photoredox Catalytic Phosphite-Mediated Deoxygenation of α-Diketones Enables Wolff Rearrangement and Staudinger Synthesis of β-Lactams
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A novel visible-light-driven catalytic activation of C=O bonds by exploiting the photoredox chemistry of 1,3,2-dioxaphospholes, readily accessible from α-diketones and trialkyl phosphites, is reported. This mild and environmentally friendly strategy provides an unprecedented and efficient access to the Wolff rearrangement reaction which traditionally entails α-diazoketones as precursors. The resulting ketenes could be precisely trapped by alcohols/thiols to give α-aryl (thio)acetates and by imines to afford the valuable β-lactams in up to 99 % yields.
- Jiang, Zhiyong,Li, Haijun,Wei, Guo,Yang, Hui
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supporting information
p. 19696 - 19700
(2021/08/03)
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- Method for catalyzing non-tension non-polar carbon-carbon single bond hydrogenolysis of dicarbonyl compound
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The invention belongs to the technical field of chemical engineering, and particularly relates to a method for catalyzing non-tension non-polar carbon-carbon single bond hydrogenolysis of a dicarbonyl compound. According to the method, in a rare earth catalysis system, a secondary alcohol (amine) compound or hydrosilyane is used as a hydrogen source, and non-tension carbon-carbon single bonds of diketone and ketone ester are subjected to hydrogenolysis to form monoketone (ester). The method is a first carbon-carbon bond hydrogenolysis reaction of ketone, and the reaction has the advantages of good atom economy, high position selectivity and chemical selectivity, mild conditions, simplicity and convenience in operation, strong functional group tolerance and the like. Diketone and ketone ester are wide in source, and application is wide when diketone and ketone ester are converted into monoketone (ester).
- -
-
Paragraph 0044-0051
(2021/08/06)
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- One-Pot Construction of Diverse Products using Versatile Cyclopropenones
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Tunable C?H activation cascade reactions between quinazolinones and cyclopropenones have been developed. Notably, cyclopropenones, acting as multi-functional building blocks, could be assembled to construct up to 10 distinct heterocyclic scaffolds in a one-pot manner. (Figure presented.).
- Huang, Tianle,Yang, Chunyan,Shi, Yuesen,Chen, Jian,Wang, Ting,Guo, Xiaoyu,Liu, Xuexin,Ding, Haosheng,Wu, Zhouping,Hai, Li,Wu, Yong
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supporting information
p. 4899 - 4904
(2021/09/14)
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- Heterogeneous Cobalt-Catalyzed C?C Bond Cleavage in Alcohols to Carbonyl Compounds
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Cobalt oxide hydrate (Co(OH)x) supported on metal oxides were prepared. The oxidative cleavage of C(OH)?C bond in alcohol was catalyzed by Co(OH)x/metal oxides using molecular oxygen as the oxidant, and the corresponding product was obtained with high selectivity. The composition and characteristics of the catalysts were analyzed by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), high-angle ring dark-field scanning TEM (HAADF-STEM), N2 physico-adsorption characterization, inductively coupled plasma optical emission spectrometry (ICP-OES), Fourier transform infrared spectrum (FTIR), X-ray photoelectron spectroscopy (XPS) and NH3-temperature-programmed desorption (NH3-TPD). Additionally, a reasonable reaction mechanism was proposed based on the characterization results and a series of controlled experiments. Notably, this heterogeneous catalytic system did not require any additives and had good recycling performance.
- Teng, Jia-nan,Zhu, Rui,Li, Xinglong,Fu, Yao
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p. 4355 - 4363
(2021/09/14)
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- Electrochemical Difunctionalization of Styrenes via Chemoselective Oxo-Azidation or Oxo-Hydroxyphthalimidation
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Atom- and step-economic oxo-azidation and oxo-hydroxyphthalimidation of styrenes have been developed under mild electrolytic conditions, respectively. Various valuable alpha-azido or hydroxyphthalimide aromatic ketones were synthesized efficiently from readily available styrenes, azides, and N-hydroxyphthalimides. Mechanism studies show that two different pathways involved in these two transformations.
- Jiang, Haobin,Wang, Feng,Ye, Zenghui,Zhang, Fengzhi,Zhu, Rongjin
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supporting information
p. 8240 - 8245
(2021/11/17)
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- Visible-Light-Driven Oxidative Cleavage of Alkenes Using Water-Soluble CdSe Quantum Dots
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The oxidative cleavage of C=C bonds is an important chemical reaction, which is a popular reaction in the photocatalytic field. However, high catalyst-loading and low turnover number (TON) are general shortcomings in reported visible-light-driven reactions. Herein, the direct oxidative cleavage of C=C bonds through water-soluble CdSe quantum dots (QDs) is described under visible-light irradiation at room temperature with high TON (up to 3.7×104). Under the same conditions, water-soluble CdSe QDs could also oxidize sulfides to sulfoxides with 51–84 % yields and TONs up to 3.4×104. The key features of this photocatalytic protocol include high TONs, wide substrates scope, low catalyst loadings, simple and mild reaction conditions, and molecular O2 as the oxidant.
- Li, Jianing,Zhao, Jingnan,Ma, Cunfei,Yu, Zongyi,Zhu, Hongfei,Yun, Lei,Meng, Qingwei
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p. 4985 - 4992
(2021/10/16)
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- Boosting free radical type photocatalysis over Pd/Fe-MOFs by coordination structure engineering
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The development of novel heterogeneous photocatalytic systems, along with a deep understanding of the relationship between the catalytic center chemical environment and the catalytic performance, is of great significance. Herein, the surface microenvironment of Pd nanoparticles was modulated with engineered Fe-MOF coordination structures (octahedron MIL-100(Fe), concave octahedron MIL-101(Fe) and irregular lumpy MIL-53(Fe)). Two heterogeneous free radical photocatalytic organic transformations have been developed over Pd nanoparticle loaded Fe-MOFs (Pd/Fe-MOFs). The photocatalytic C-H arylation of thiazole and decarboxylation cross-coupling with cinnamic acid were investigated. Thiazole C-H arylation with halobenzenes was brought about through C-halogen bond activation with the photogenerated electron-rich Pd NPs, the aryl radical generation and the follow-up radical addition. The cinnamic acid decarboxylation cross-coupling was also achieved by means of C-halogen bond activation with photogenerated electron-rich Pd NPs. The base regulated the product stereoselectivity by affecting the balance between cinnamic acid and carboxylate anions, as well as the balance between aryl radicals and the coordination complex intermediates. The improvement of the heterogeneous photocatalytic performance for thiazole C-H arylation and cinnamic acid decarboxylation cross-coupling should be ascribed to the difference in the electron transfer efficiency to Pd NPs over various engineered Fe-O cluster coordination structures. This work highlights the importance of exploiting structure engineering for heterogeneous photocatalytic systems.
- Bian, Fengxia,Cheng, Hongmei,Dong, Fan,Jiang, Heyan,Jiang, Yanke,Yang, Lin,Zang, Cuicui
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p. 5543 - 5552
(2021/08/25)
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- Synthesis of α-Ketoimidoyl Fluorides via Geminal Fluorine-Promoted Azide Rearrangement
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Despite the promising synthetic potential, the utilization of imidoyl fluorides has been hampered by the lack of broadly applicable preparative methods. Herein, bench-stable α-ketoimidoyl fluorides were synthesized from geminal chlorofluorides through tandem azidation/rearrangement under mild conditions. The efficiency was consistently high, regardless of the steric and electronic environments. The synthetic utility of the α-ketoimidoyl fluoride was also demonstrated. Furthermore, the remarkable accelerating effect of the geminal fluorine substituent was identified and rationalized by density functional theory calculation.
- Kim, Ha Eun,Choi, Jun-Ho,Chung, Won-Jin
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supporting information
p. 8810 - 8815
(2021/11/20)
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- Cu(ii)Cl2containing bispyridine-based porous organic polymer support preparedviaalkyne-azide cycloaddition as a heterogeneous catalyst for oxidation of various olefins
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A new type of porous organic polymer (POP) based heterogeneous catalystCu-POPwas prepared by immobilizing Cu(ii)Cl2into bpy containing POP preparedviaalkyne-azide cycloaddition. This new catalyst showed efficient catalytic activities and outstanding reusability. Remarkably, one batch ofCu-POPwas continuously used for all olefins without losing its activity by simply washing.
- Choi, Hye Min,Lee, Suk Joong,Yoon, Jongho
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supporting information
p. 9149 - 9152
(2020/06/17)
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- Biochar as supporting material for heterogeneous Mn(II) catalysts: Efficient olefins epoxidation with H2O2
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A novel type of hybrid catalytic materials [MnII-L?BC] has been developed using biochar (BC) as support material for covalent grafting of a MnII Schiff-base catalyst (MnII-L). The hybrid [MnII-L?BC] materials have been evaluated for an important catalytic process, epoxidation of olefins using H2O2 as oxidant. A number of different substrates were used, with cyclohexene achieving the highest yields. When compared to the non-grafted, homogeneous MnII-L, the hybrid catalysts [MnII-L?BC] show a significant enhancement of the catalytic efficiency i.e. as documented by the increase of Turnover Numbers (TONs) (826 for [MnII-L-SS550ox] and 822 for [MnII-L-SW550ox]) and Turnover Frequencies (TOFs) (551 h?1 for [MnII-L-SS550ox] and 411 h?1 for [MnII-L-SW550ox]). The interfacial catalytic mechanism and the role of the BC support have been analyzed by Raman and Electron Paramagnetic Resonance spectroscopies. Based on these data we discuss a mechanism where the high efficiency of the hybrid materials involves the biochar carbon layers acting as promoters of the substrate and products kinetics. To a broader context, this work exemplifies that biochar-based hybrid materials are potent for oxidative catalysis technologies.
- Borges Regitano, Jussara,Deligiannakis, Yiannis,Gemenetzi, Aikaterini,Louloudi, Maria,Mavrogiorgou, Alexandra,Pierri, Leticia
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- Visible-light-induced oxidative lignin c-c bond cleavage to aldehydes using vanadium catalysts
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Lignin is the largest carrier of aromatics on earth, and its depolymerization can afford value-Added aromatic products. Direct cleavage of the C-C bonds in lignin linkages is significant, but it is challenging to obtain low-molecular-weight aromatic monomers. Herein, using vanadium catalysts under visible light, we selectively cleave the C-C bonds in β-1 and β-O-4 interlinkages occluded in lignin models and extracts by an oxidative protocol. Visible light irradiation triggered single electron transfer between the substrate and the catalyst, which further induced the selective Cα-Cβ bond cleavage and generated the final aromatic products through radical intermediates. Using this photocatalytic chemistry, the reactivity of lignin models and the selectivity of Cα-Cβ bond cleavage were significantly improved. More importantly, this protocol affords aromatic monomers through the fragmentation of organosolv lignins even at room temperature, indicating the potential of photocatalytic C-C bond cleavage of lignin linkages under ambient conditions.
- Liu, Huifang,Li, Hongji,Luo, Nengchao,Wang, Feng
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p. 632 - 643
(2020/01/02)
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- Diazaphosphinyl radical-catalyzed deoxygenation of α-carboxy ketones: A new protocol for chemo-selective C-O bond scission: Via mechanism regulation
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C-O bond cleavage is often a key process in defunctionalization of organic compounds as well as in degradation of natural polymers. However, it seldom occurs regioselectively for different types of C-O bonds under metal-free mild conditions. Here we report a facile chemo-selective cleavage of the α-C-O bonds in α-carboxy ketones by commercially available pinacolborane under the catalysis of diazaphosphinane based on a mechanism switch strategy. This new reaction features high efficiency, low cost and good group-tolerance, and is also amenable to catalytic deprotection of desyl-protected carboxylic acids and amino acids. Mechanistic studies indicated an electron-transfer-initiated radical process, underlining two crucial steps: (1) the initiator azodiisobutyronitrile switches originally hydridic reduction to kinetically more accessible electron reduction; and (2) the catalytic phosphorus species upconverts weakly reducing pinacolborane into strongly reducing diazaphosphinane. This journal is
- Cheng, Jin-Pei,Yang, Jin-Dong,Zhang, Jingjing
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p. 8476 - 8481
(2020/09/07)
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- Light and oxygen-enabled sodium trifluoromethanesulfinate-mediated selective oxidation of C-H bonds
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Visible light-induced organic reactions are important chemical transformations in organic chemistry, and their efficiency highly depends on suitable photocatalysts. However, the commonly used photocatalysts are precious transition-metal complexes and elaborate organic dyes, which hamper large-scale production due to high cost. Here, for the first time, we report a novel strategy: light and oxygen-enabled sodium trifluoromethanesulfinate-mediated selective oxidation of C-H bonds, allowing high-value-added aromatic ketones and carboxylic acids to be easily prepared in high-to-excellent yields using readily available alkyl arenes, methyl arenes and aldehydes as materials. The mechanistic investigations showed that the treatment of inexpensive and readily available sodium trifluoromethanesulfinate with oxygen under irradiation of light could in situ form a pentacoordinate sulfide intermediate as an efficient photosensitizer. The method represents a highly efficient, economical and environmentally friendly strategy, and the light and oxygen-enabled sodium trifluoromethanesulfinate photocatalytic system represents a breakthrough in photochemistry. This journal is
- Fu, Hua,Liu, Can,Liu, Yong,Yang, Haijun,Zhu, Xianjin
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supporting information
p. 4357 - 4363
(2020/07/14)
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- Synthesis and Catalytic Properties of Metal- N-Heterocyclic-Carbene-Decorated Covalent Organic Framework
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We demonstrate herein that the N-heterocyclic-carbene (NHC)-metal complex (NHC-M)-involved covalent organic framework (COF) can be prepared by the direct polymerization of the NHC-M monomer with its counterpart under solvothermal conditions. The NHC-M-COF with different counterions is readily achieved via solid-state anion exchange. The obtained NHC-AuX-COF (X = Cl- and SbF6-) can be a highly active reusable catalyst to separately promote the carboxylation of the terminal alkyne with CO2 and alkyne hydration under mild conditions.
- Dong, Ying,Dong, Yu-Bin,Kan, Jing-Lan,Li, Yue,Wu, Xiaowei
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supporting information
p. 7363 - 7368
(2020/10/12)
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- Cobalt-Catalyzed Reductive C-O Bond Cleavage of Lignin β-O-4 Ketone Models via in Situ Generation of the Cobalt-Boryl Species
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An efficient and mild method for reductive C-O bond cleavage of lignin β-O-4 ketone models was developed to afford the corresponding ketones and phenols with PDI-CoCl2 as the precatalyst and diboron reagent as the reductant. The synthetic utility of the methodology was demonstrated by depolymerization of a polymeric model and gram-scale transformation. Mechanistic studies suggested that this transformation involves steps of carbonyl insertion, 1,2-Brook type rearrangement, β-oxygen elimination, and rate-limiting regeneration of the catalytic active Co-B species.
- Gao, Kecheng,Xu, Man,Cai, Cheng,Ding, Yanghao,Chen, Jianhui,Liu, Bosheng,Xia, Yuanzhi
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p. 6055 - 6060
(2020/08/12)
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- Blue Light Promoted Difluoroalkylation of Aryl Ketones: Synthesis of Quaternary Alkyl Difluorides and Tetrasubstituted Monofluoroalkenes
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A facile and cost-effective method for the preparation of fluoroalkylated compounds has been described by the direct photoexcitation of halofluoroalkanes with blue light absorptivity, enabling the difluoroalkylation of aryl ketones. The methodology has provided an efficient, mild, and catalyst-free synthetic method for quaternary difluoroalkylated arenes and tetrasubstituted monofluoroalkenes.
- Li, Kangkui,Chen, Jingchao,Yang, Chunhui,Zhang, Keyang,Pan, Chunxiang,Fan, Baomin,Fan, Baomin
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supporting information
p. 4261 - 4265
(2020/06/04)
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- Electronic Asymmetry of an Annelated Pyridyl-Mesoionic Carbene Scaffold: Application in Pd(II)-Catalyzed Wacker-Type Oxidation of Olefins
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The two donor modules of an annelated pyridyl-mesoionic carbene ligand (aPmic) have different σ- and π-bonding characteristics leading to its electronic asymmetry. A Pd(II) complex 1 featuring aPmic catalyzes the oxidation of a wide range of terminal olefins to the corresponding methyl ketones in good to excellent yields in acetonitrile. The catalytic reaction is proposed to proceed via syn-peroxypalladation and a subsequent rate-limiting 1,2-hydride shift, which is supported by kinetic studies. The electronic asymmetry of aPmic renders a well-defined coordination sphere at Pd. The favored arrangement of reactants on the metal center features an olefin trans to the pyridyl module and a tbutylperoxide trans to the carbene. This arrangement gains added stability by the π-delocalization paved by the compatible orbitals on Pd, the pyridyl module, and the olefin that is perpendicular to the Pd(aPmic) plane. The π-interactions are absent in an alternate arrangement wherein the olefin is trans to the carbene. Density functional theory studies reveal the matching orbital overlaps responsible for the preferred arrangement over the other. This work provides an orbital description for the electronic asymmetry of aPmic.
- Bera, Jitendra K.,Dutta, Indranil,Kunnikuruvan, Sooraj,Reshi, Noor U Din,Saha, Sayantani,Yadav, Suman
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p. 11385 - 11393
(2020/11/23)
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- Method for producing methyl ketone by catalytic oxidation of olefin by palladium
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The invention discloses a method for generating methyl ketone by catalyzing oxidization of olefin with palladium. The method comprises the following steps: performing a full reaction and a TLC (Thin Layer Chromatography) track reaction in an organic solvent by taking end-position olefin or a nonterminal olefin compound as a raw material, hydrogen peroxide or hydrogen peroxide tertiary butanol as an oxidizing agent, palladium acetate as a catalyst and inorganic acid as a promoter; extracting with ethyl acetate after finishing the reaction, and performing suction filtration, concentration and purification to obtain a corresponding methyl ketone compound. By adopting the method, the palladium acetate is taken as the catalyst, the application of an expensive palladium complex catalyst is avoided; the hydrogen peroxide or the hydrogen peroxide tertiary butanol is taken as the oxidizing agent, a completely-decomposed product is environment-friendly; the inorganic acid is used in a catalytic amount, so that the influences on the environment and equipment are small; treatment difficulty is lowered by using a low-boiling-point organic solvent; the reaction process is environment-friendly, and treatment is easy after reaction; meanwhile, the method is suitable for the end-position olefin or the nonterminal olefin compound, and is wide in application substrate rang; the defect of low applicability of the conventional Wacker oxidizing reaction is overcome.
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-
Paragraph 0038; 0039
(2020/09/20)
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- Manganese/Copper Co-catalyzed Electrochemical Wacker-Tsuji-Type Oxidation of Aryl-Substituted Alkenes
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A manganese/copper co-catalyzed electrochemical Wacker-Tsuji-type oxidation of aryl-substituted alkenes has been developed. The process involves the use of 5 mol % MnBr2 and 7.5 mol % CuCl2, in 4:1 acetonitrile/water in an undivided cell at 60 °C, with 2.8 V constant applied potential. α-Aryl ketones are formed in moderate to excellent yields, with the advantages of avoidance of palladium as a catalyst and any external chemical oxidant in an easily operated, cost-effective procedure.
- Lai, Junshan,Pericàs, Miquel A.
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supporting information
p. 7338 - 7342
(2020/10/02)
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