- Cleavage∕cross-coupling strategy for converting β-O-4 linkage lignin model compounds into high valued benzyl amines via dual C–O bond cleavage
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Lignin is the most recalcitrant of the three components of lignocellulosic biomass. The strength and stability of the linkages have long been a great challenge for the degradation and valorization of lignin biomass to obtain bio-fuels and commercial chemicals. Up to now, the selective cleavage of C–O linkages of lignin to afford chemicals contains only C, H and O atoms. Our group has developed a cleavage/cross-coupling strategy for converting 4-O-5 linkage lignin model compounds into high value-added compounds. Herein, we present a palladium-catalyzed cleavage/cross-coupling of the β-O-4 lignin model compounds with amines via dual C–O bond cleavage for the preparation of benzyl amine compounds and phenols.
- Jia, Le,Li, Chao-Jun,Zeng, Huiying
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supporting information
(2021/10/29)
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- Synthesis of Cyclobutanones by Gold(I)-Catalyzed [2 + 2] Cycloaddition of Ynol Ethers with Alkenes
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A broad scope synthesis of cyclobutanones by gold(I)-catalyzed [2 + 2] cycloaddition of ynol ethers with alkenes has been developed. We also found that internal aryl ynol ethers can undergo (4 + 2) cycloaddition reaction with alkenes leading to the corres
- Zanini, Margherita,Cataffo, Andrea,Echavarren, Antonio M.
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supporting information
p. 8989 - 8993
(2021/11/20)
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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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supporting information
p. 6055 - 6060
(2020/08/12)
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- Multiple Mechanisms Mapped in Aryl Alkyl Ether Cleavage via Aqueous Electrocatalytic Hydrogenation over Skeletal Nickel
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We present here detailed mechanistic studies of electrocatalytic hydrogenation (ECH) in aqueous solution over skeletal nickel cathodes to probe the various paths of reductive catalytic C-O bond cleavage among functionalized aryl ethers relevant to energy science. Heterogeneous catalytic hydrogenolysis of aryl ethers is important both in hydrodeoxygenation of fossil fuels and in upgrading of lignin from biomass. The presence or absence of simple functionalities such as carbonyl, hydroxyl, methyl, or methoxyl groups is known to cause dramatic shifts in reactivity and cleavage selectivity between sp3 C-O and sp2 C-O bonds. Specifically, reported hydrogenolysis studies with Ni and other catalysts have hinted at different cleavage mechanisms for the C-O ether bonds in α-keto and α-hydroxy β-O-4 type aryl ether linkages of lignin. Our new rate, selectivity, and isotopic labeling results from ECH reactions confirm that these aryl ethers undergo C-O cleavage via distinct paths. For the simple 2-phenoxy-1-phenylethane or its alcohol congener, 2-phenoxy-1-phenylethanol, the benzylic site is activated via Ni C-H insertion, followed by beta elimination of the phenoxide leaving group. But in the case of the ketone, 2-phenoxyacetophenone, the polarized carbonyl πsystem apparently binds directly with the electron rich Ni cathode surface without breaking the aromaticity of the neighboring phenyl ring, leading to rapid cleavage. Substituent steric and electronic perturbations across a broad range of β-O-4 type ethers create a hierarchy of cleavage rates that supports these mechanistic ideas while offering guidance to allow rational design of the catalytic method. On the basis of the new insights, the usage of cosolvent acetone is shown to enable control of product selectivity.
- Hegg, Eric L.,Jackson, James E.,Klinger, Grace E.,Saffron, Christopher M.,Zhou, Yuting
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supporting information
p. 4037 - 4050
(2020/03/10)
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- Synthesis of benzofurans from the cyclodehydration of α-phenoxy ketones mediated by Eaton’s reagent
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Cyclodehydration of α-phenoxy ketones promoted by Eaton’s reagent (phosphorus pentoxide–methanesulfonic acid) is used to prepare 3-substituted or 2,3-disubstituted benzofurans with moderate to excellent yields under mild conditions. The method provides a facile access to benzofurans from readily available starting materials such as phenols and α-bromo ketones. The reaction is highly efficient, which is attributed to the good reactivity and fluidity of Eaton’s reagent. The reaction can be applied to prepare naphthofurans, furanocoumarins, benzothiophenes, and benzopyrans.
- Ma, Lin,Ma, Zhanwei,Zhang, Min,Zhou, Min
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p. 426 - 436
(2020/03/23)
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- Copper-catalyzed synthesis of benzanilides from lignin model substrates 2-phenoxyacetophenones under an air atmosphere
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The synthesis of chemicals from biomass-derived compounds is an interesting and challenging topic. In this work, using the lignin-derived 2-phenoxyacetophenones as the feedstock we present a novel approach for the synthesis of benzanilides via the reaction of 2-phenoxyacetophenones with anilines catalyzed by CuCl2 in DMSO at 120 °C under an air atmosphere. This approach has wide scope for 2-phenoxyacetophenones and anilines, and various benzanilides accompanied by the corresponding phenols could be obtained in high yields via changing the 2-phenoxyacetophenones and anilines. The reaction mechanism study indicated that the oxidative cleavage of the C-C bond in 2-phenoxyacetophenones and the formation of a C-N bond occurred simultaneously in the reaction process, resulting in the formation of benzanilides together with phenols.
- Liu, Xinwei,Zhang, Hongye,Wu, Cailing,Chen, Yu,Yu, Bo,Liu, Zhimin,Liu, Zhenghui
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p. 1223 - 1227
(2018/02/06)
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- Self-hydrogen transfer hydrogenolysis of β-O-4 linkages in lignin catalyzed by MIL-100(Fe) supported Pd-Ni BMNPs
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A MIL-100(Fe) supported Pd-Ni BMNP catalyst has been fabricated, and the catalyst exhibits superior catalytic performance toward the intramolecular transfer hydrogenolysis of lignin model compounds and organosolv lignin. Alcoholic groups (CαH-OH) of lignin were exploited as the hydrogen source, and selective cleavage of β-O-4 linkages in lignin was realized without an extra hydrogen donor. This protocol was suitable for organosolv lignin as well as model compounds; several phenols and functionalized acetophenones were detected when extracted lignin was treated in our system. The catalyst exhibits outstanding catalytic stability during the reaction process, which can be ascribed to the porous structure and the strong water stability of MIL-100(Fe). The excellent catalytic performance of Pd1Ni4/MIL-100(Fe) highlights the "synergistic effect" between the BMNPs and the functional synergy between MNPs and MOFs, and our work shows the bright future of BMNPs and MOFs in the development of catalysts for sustainable chemistry.
- Zhang, Jia-Wei,Lu, Guo-Ping,Cai, Chun
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supporting information
p. 4538 - 4543
(2017/10/13)
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- Facile and selective hydrogenolysis of β-O-4 linkages in lignin catalyzed by Pd-Ni bimetallic nanoparticles supported on ZrO2
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The β-O-4 linkage in lignin can be selectively cleaved by Pd-Ni bimetallic nanoparticles supported on ZrO2 using hydrogen gas as the hydrogen donor under ambient pressure and neutral conditions. Conspicuous enhancement in activity is observed compared with single nickel and palladium catalysts based on the results of experiments and characterization. Moreover, hydrogenation of the produced phenols is tuned by adjusting the amount of NaBH4. The catalyst can be reused over ten times in the model reaction and over five times in the hydrogenolysis of lignin without an obvious change in activity and selectivity.
- Zhang, Jia-Wei,Cai, Yao,Lu, Guo-Ping,Cai, Chun
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supporting information
p. 6229 - 6235
(2016/12/03)
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- Structural design, synthesis and structure-activity relationships of thiazolidinones with enhanced anti-Trypanosoma cruzi activity
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Pharmacological treatment of Chagas disease is based on benznidazole, which displays poor efficacy when administered during the chronic phase of infection. Therefore, the development of new therapeutic options is needed. This study reports on the structural design and synthesis of a new class of anti-Trypanosoma cruzi thiazolidinones (4 a-p). (2-[2-Phenoxy-1-(4-bromophenyl) ethylidene)hydrazono]-5-ethylthiazolidin-4-one (4 h) and (2-[2-phenoxy-1-(4- phenylphenyl)ethylidene)hydrazono]-5-ethylthiazolidin-4-one (4 l) were the most potent compounds, resulting in reduced epimastigote proliferation and were toxic for trypomastigotes at concentrations below 10 μM, while they did not display host cell toxicity up to 200 μM. Thiazolidinone 4 h was able to reduce the in vitro parasite burden and the blood parasitemia in mice with similar potency to benznidazole. More importantly, T. cruzi infection reduction was achieved without exhibiting mouse toxicity. Regarding the molecular mechanism of action, these thiazolidinones did not inhibit cruzain activity, which is the major trypanosomal protease. However, investigating the cellular mechanism of action, thiazolidinones altered Golgi complex and endoplasmic reticulum (ER) morphology, produced atypical cytosolic vacuoles, as well as induced necrotic parasite death. This structural design employed for the new anti-T. cruzi thiazolidinones (4 a-p) led to the identification of compounds with enhanced potency and selectivity compared to first-generation thiazolidinones. These compounds did not inhibit cruzain activity, but exhibited strong antiparasitic activity by acting as parasiticidal agents and inducing a necrotic parasite cell death. Stop the cycle! The attachment of an aryl ring to the iminic carbon produced thiazolidinones that are conformationally more restricted than first-generation thiazolidinones. This enhanced the potency of antiparasitic thiazolidinones, as observed under treatment with compound 4 h where parasite development and invasion in host cells were substantially reduced. Copyright
- Moreira, Diogo Rodrigo Magalhaes,Lima Leite, Ana Cristina,Cardoso, Marcos Verissimo Oliveira,Srivastava, Rajendra Mohan,Hernandes, Marcelo Zaldini,Rabello, Marcelo Montenegro,Da Cruz, Luana Faria,Ferreira, Rafaela Salgado,De Simone, Carlos Alberto,Meira, Cassio Santana,Guimaraes, Elisalva Teixeira,Da Silva, Aline Caroline,Dos Santos, Thiago Andre Ramos,Pereira, Valeria Rego Alves,Pereira Soares, Milena Botelho
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supporting information
p. 177 - 188
(2014/01/17)
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- Liquid chromatographic resolution of mexiletine and its analogs on crown ether-based chiral stationary phases
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Mexiletine, an effective class IB antiarrhythmic agent, and its analogs were resolved on three different crown ether-based chiral stationary phases (CSPs), one (CSP 1) of which is based on (+)-(18-crown-6)-2,3,11,12- tetracarboxylic acid and the other two (CSP 2 and CSP 3) are based on (3,3'-diphenyl-1,1'-binaphthyl)-20-crown-6. Mexiletine was resolved with a resolution (RS) of greater than 1.00 on CSP 1 and CSP 3 containing residual silanol group-protecting n-octyl groups on the silica surface, but with a resolution (RS) of less than 1.00 on CSP 2. The chromatographic behaviors for the resolution of mexiletine analogs containing a substituted phenyl group at the chiral center on the three CSPs were quite dependent on the phenoxy group of analytes. Namely, mexiletine analogs containing 2,6-dimethylphenoxy, 3,4-dimethylphenoxy, 3-methylphenoxy, 4-methylphenoxy, and a simple phenoxy group were resolved very well on the three CSPs even though the chiral recognition efficiencies vary with the CSPs. However, mexiletine analogs containing 2-methylphenoxy group were not resolved at all or only slightly resolved. Among the three CSPs, CSP 3 was found to show the highest chiral recognition efficiencies for the resolution of mexiletine and its analogs, especially in terms of resolution (RS). Chirality 26:272-278, 2014. 2014 Wiley Periodicals, Inc.
- Jin, Kab Bong,Kim, Hee Eun,Hyun, Myung Ho
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p. 272 - 278
(2014/05/06)
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- Chiral epoxides via borane reduction of 2-haloketones catalyzed by spiroborate ester: Application to the synthesis of optically pure 1,2-hydroxy ethers and 1,2-azido alcohols
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An enantioselective borane-mediated reduction of a variety of 2-haloketones with 10% spiroaminoborate ester 1 as catalyst is described. By a simple basic workup of 2-halohydrins, optically active epoxides are obtained in high yield and with excellent enantiopurity (up to 99% ee). Ring-opening of oxiranes with phenoxides or sodium azide is investigated under different reaction conditions affording nonracemic 1,2-hydroxy ethers and 1,2-azido alcohols with excellent enantioselectivity (99% ee) and in good to high chemical yield. 2011 American Chemical Society.
- Huang, Kun,Wang, Haiyang,Stepanenko, Viatcheslav,De Jesus, Melvin,Torruellas, Carilyn,Correa, Wildeliz,Ortiz-Marciales, Margarita
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supporting information; scheme or table
p. 1883 - 1886
(2011/06/20)
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- Mechanistic insights into the rhodium-catalyzed intramolecular ketone hydroacylation
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[Rh((fl)-DTBM-SEGPHOS)]BF4 catalyzes the intramolecular hydroacylation of ketones to afford seven-membered lactones in large enantiomeric excess. Herein, we present a combined experimental and theoretical study to elucidate the mechanism and origin of selectivity in this C-H bond activation process. Evidence is presented for a mechanistic pathway involving three key steps: (1) rhodium(I) oxidative addition into the aldehyde C-H bond, (2) insertion of the ketone C=O double bond into the rhodium hydride, and (3) C-O bond-forming reductive elimination. Kinetic isotope effects and Hammett plot studies support that ketone insertion isthe turnover-limiting step. Detailed kinetic experiments were performed using both 1,3- bis(diphenylphosphino)propane (dppp) and (R)-DTBM-SEGPH OS as ligands. With dppp, the keto-aldehyde substrate assists in dissociating a dimeric precatalyst 8 and binds an active monomeric catalyst 9. With [Rh((R)-DTBM-SEGPHOS)]BF4, there is no induction period and both substrate and product inhibition are observed. In addition, competitive decarbonylation produces a catalytically inactive rhodium carbonyl species that accumulates over the course of the reaction. Both mechanisms were modeled with a kinetics simulation program, and the models were consistent with the experimental data. Density functional theory calculations were performed to understand more elusive details of this transformation. These simulations support that the ketone insertion step has the highest energy transition state and reveal an unexpected interactionbetween the carbonyl-oxygen lone pair and a Rh d-orbital in this transi tion state structure. Finally, a model based on the calculated transition-state geometry is proposed to rationalize the absolute sense of enantioinduction observed using (R)-DTBM-SEGPHOS as the chiral ligand.
- Shen, Zengming,Dornan, Peter K.,Khan, Hasan A.,Woo, Tom K.,Dong, Vy M.
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supporting information; experimental part
p. 1077 - 1091
(2009/06/28)
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- Biomimetic transfer hydrogenation of 2-alkoxy- and 2-aryloxyketones with iron-porphyrin catalysts
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In situ generated iron porphyrins are applied as homogeneous catalysts in the transfer hydrogenation of α-substituted ketones. Using 2-propanol as hydrogen donor various protected 1,2-hydroxyketones are reduced to the corresponding mono-substituted 1,2-di
- Enthaler, Stephan,Spilker, Bj?rn,Erre, Giulia,Junge, Kathrin,Tse, Man Kin,Beller, Matthias
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p. 3867 - 3876
(2008/09/20)
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- CHEMICAL COMPOUNDS
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Compounds of formula (I):wherein variable groups are as defined within; for use in the inhibition of 11betaHSD1 are described
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- Photochemical Generation of Radical Anions of Photolabile Aryl Ketones
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The radical anions of a series of substituted α-(aryloxy)acetophenones have been generated by trapping the solvated electron produced by 355-nm laser-induced photoionization of 4,4'-dimethoxystilbene in either acetonitrile or dimethylformamide (DMF).The radical anion of the parent ketone, α-phenoxyacetophenone, has λmax at 500 nm and decays with a rate constant 7 x 1E5 s-1.This rate constant reflects the rate of β-cleavage to generate phenoxide ion and phenylacyl radical.The rate constant for β-cleavage decreases for ketones with electron donating substituents in the α-aryloxy ring.Substituent effects on the acetophenone ring are in the opposite direction, and many of the 4-substituted (aryloxy)acetophenones have half-lives in excess of 10 μs that reflect a combination of second order processes and are not limited by β-cleavage.The generality of the photoionization/electron trapping method for the generation of radical anions of ketones with short-lived excited states that preclude direct excitation is illustrated by its application to other aryl ketones that undergo α-cleavage, β-phenyl quenching, and intramolecular hydrogen abstraction reactions.
- Mathivanan, N.,Johnston, L. J.,Wayner, D.D.M.
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p. 8190 - 8195
(2007/10/02)
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- Synthesis and calcium antagonistic activity of a series of diethyl benzofuryl, benzothienyl and benzogammapyronyl benzylphosphonates
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In this work we present about 15 original heterocyclic diethyl benzylphosphonate analogues of fostedil, in which we have varied the nature of the heterocycle, the substituents or the phosphonic group, or even the position of this latter.Three diethyl 4-(2
- Baziard-Mouysset, G.,Tchani, G. W.,Stigliani, J. L.,Payard, M.,Bonnafous, R.,Tisne-Versailles, J.
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p. 539 - 546
(2007/10/02)
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