- Ene Reductase Enzymes for the Aromatisation of Tetralones and Cyclohexenones to Naphthols and Phenols
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Ene reductases (EREDs) have great potential as oxidation biocatalysts, as demonstrated by their efficient conversion of a number of tetralones to the corresponding naphthols. Of 96 enzymes tested, 57 were able to produce 2-naphthol in this way. Further tests with substituted tetralones revealed typically high conversions up to >99%. The reactions were performed under mild conditions in aqueous buffer with only co-solvent, biocatalyst and oxidation substrate required for conversion. Production of a methoxy-substituted naphthol was also successfully performed on a gram scale, with 91% yield. This methodology provides a new avenue to produce substituted naphthols as valuable building blocks, with the possibility to extend the approach to the production of phenols also being demonstrated.
- Kelly, Paul P.,Lipscomb, David,Quinn, Derek J.,Lemon, Ken,Caswell, Jill,Spratt, Jenny,Kosjek, Birgit,Truppo, Matthew,Moody, Thomas S.
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- Noble Metal Supported on Activated Carbon for “Hydrogen Free” HDO Reactions: Exploring Economically Advantageous Routes for Biomass Valorisation
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An innovative route for bio-compounds upgrading via “hydrogen-free” hydrodeoxygenation (HDO) is proposed and evaluated using guaiacol as a model compound in a high-pressure batch reactor. Experimental results showed that noble metal supported on activated carbon catalysts are able to conduct tandem multiple steps including water splitting and subsequent HDO. The activity of Ru/C catalyst is superior to other studied catalysts (i. e. Au/C, Pd/C and Rh/C) in our water-only HDO reaction system. The greater dispersion and smaller metal particle size confirmed by the TEM micrographs accounts for the better performance of Ru/C. This material also presents excellent levels of stability as demonstrated in multiple recyclability runs. Overall, the proposed novel approach confirmed the viability of oxygenated bio-compounds upgrading in a water-only reaction system suppressing the need of external H2 supply and can be rendered as a fundamental finding for the economical biomass valorisation to produce added value bio-fuels.
- Jin, Wei,Santos, José Luis,Pastor-Perez, Laura,Gu, Sai,Centeno, Miguel Angel,Reina, Tomas Ramirez
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- Postsynthetic metalation of bipyridyl-containing metal-organic frameworks for highly efficient catalytic organic transformations
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We have designed highly stable and recyclable single-site solid catalysts via postsynthetic metalation of the 2,2-bipyridyl-derived metal-organic framework (MOF) of the UiO structure (bpy-UiO). The Ir-functionalized MOF (bpy-UiO-Ir) is a highly active catalyst for both borylation of aromatic C-H bonds using B2(pin)2 (pin = pinacolate) and ortho-silylation of benzylicsilyl ethers; the ortho-silylation activity of the bpy-UiO-Ir is at least 3 orders of magnitude higher than that of the homogeneous control. The Pd-functionalized MOF (bpy-UiO-Pd) catalyzes the dehydrogenation of substituted cyclohexenones to afford phenol derivatives with oxygen as the oxidant. Most impressively, the bpy-UiO-Ir was recycled and reused 20 times for the borylation reaction without loss of catalytic activity or MOF crystallinity. This work highlights the opportunity in designing highly stable and active catalysts based on MOFs containing nitrogen donor ligands for important organic transformations.
- Manna, Kuntal,Zhang, Teng,Lin, Wenbin
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- Kinetic analysis and reaction mechanism for anisole conversion over zirconia-supported molybdenum oxide
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Gas-phase catalytic conversion of anisole and its reaction intermediates was studied over a 10 wt% MoO3/ZrO2 catalyst at temperatures between 553 and 633 K and H2 partial pressures (PH2) ≤ 1 bar. Benzene, phenol, cresol and methyl anisole were identified as the primary products from the hydrodeoxygenation (HDO), hydrogenolysis, intra- and intermolecular alkylation of anisole, respectively. The anisole to benzene conversion featured a first-order dependence with respect to PH2, while the conversion of phenol to benzene and m-cresol to toluene, showed PH2 and Poxygenate reaction orders of 1/2 and zero, respectively. A kinetic model showed that although the secondary pathway of phenol HDO to benzene has a rate constant ～3 times higher than that for the HDO of anisole to benzene, the anisole HDO pathway is dominant at low anisole conversions. Apparent orders of ～? with Poxygenate for anisole hydrogenolysis and alkylation to form phenol, cresol, and methyl anisole implied the existence of different active sites than those responsible for HDO. Co-feed studies with H2O, pyridine, and di-tert butyl pyridine (DTBP) indicated that the active-sites responsible for HDO have a Lewis acid character that is associated with oxygen vacancies and that is distinct from the nature of sites responsible for hydrogenolysis and alkylation. Accordingly, co-feeding CH3OH resulted in increased phenol alkylation rates to form alkylated cresols along with inhibition of phenol to benzene HDO rates. A three-site model was proposed to unify the HDO, hydrogenolysis, and alkylation reactivity data obtained from the kinetic and co-feed studies.
- Shetty, Manish,Anderson, Eric M.,Green, William H.,Román-Leshkov, Yuriy
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- Continuous-flow generation of anhydrous diazonium species: Monolithic microfluidic reactors for the chemistry of unstable intermediates
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Monolithic microfluidic reactors for the safe, expedient, and continuous synthesis of products involving unstable intermediates were fabricated and assessed. The formation of diazonium salts in anhydrous conditions and their subsequent in situ chlorination within microfiuidic channels under hydrodynamic pumping regimes is presented. Significant enhancements in yield were observed due to enhanced heat and mass transfer in microfluidic systems. Analysis performed using off-line GC and GC-MS was compared with on-line, on-chip Raman spectroscopy for the direct determination of analytes.
- Fortt, Robin,Wootton, Robert C. R.,De Mello, Andrew J.
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- Influence of Re addition to Ni/SiO2 catalyst on the reaction network and deactivation during hydrodeoxygenation of m-cresol
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The reaction network of hydrodeoxygenation of m-cresol was investigated over Ni/SiO2 and Ni-Re/SiO2 catalysts at 300 °C and 1 atm H2. m-Cresol conversion proceeds through three major primary pathways: phenyl ring hydrogenation to 3-methylcyclohexanone and 3-methylcyclohexanol, C[sbnd]C hydrogenolysis to CH4 and phenol, and deoxygenation to toluene. Re addition promotes dehydrogenation of the initially formed methylcyclohexanone and methylcyclohexanol to surface intermediates followed by deoxygenation toward formation of toluene. C[sbnd]C hydrogenolysis happens on unsaturated compounds with phenyl ring, instead of saturated compounds, since dehydrogenation is requested prior to C[sbnd]C cleavage. The turnover frequency (TOF) for CH4 formation follows the order of m-cresol 4. Re addition not only promotes deoxygenation to toluene by providing active Ni-Re neighboring sites, but also inhibits the aromatics hydrogenolysis to CH4, resulting in high toluene selectivity on bimetallic catalyst. Both catalysts show a similar deactivation trend and coke is speculated to be the major reason for deactivation.
- Ge, Qingfeng,Han, Jinyu,Wang, Hua,Yang, Feifei,Zhu, Xinli
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- One-pot synthesis of benzofurans via heteroannulation of benzoquinones
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Three different reactions were explored leading to the synthesis of various benzofurans. All reactions took place under AcOH catalysis in a one-pot manner. As a result, benzoquinone derivatives underwent heteroannulation with either itself or cyclohexanones to produce furanylidene-benzofuran or benzofuran structures, respectively.
- Pirouz, Maryam,Saeed Abaee,Harris, Pernille,Mojtahedi, Mohammad M.
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- Photochemical Transformationos of Protonated Phenols. A One-Step Synthesis of Umbellulone from Thymol
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UV irradiation of thymol (7) at 254 or 300 nm in trifluoromethanesulfonic acid affords ten products, eight of which have been isolated and characterized.Four competitive processes are suggested to be operating in the formation of the photoproducts: (i) regioselective type A rearrangement leading to umbellulone (8, about 10percent, (ii) formal C2->C3 migration by type A rearrangement and ring opening which affords the principal products, 3-isopropyl-5-methylphenol (12, 17percent), (iii) intermolecular transalkylation leading to diisopropylphenols 13-15 (17percent), and (iv) formation ofpiperitenone (10, 5percent) initiated by hydrogen abstraction.A mechanism for the formation of 10 is proposed.Both para- and ortho-protonated 7 are suggested to be involved in product formation.
- Baeckstroem, Peter,Jacobsson, Ulla,Koutek, Bohumir,Norin, Torbjoern
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- Selective conversion of m-cresol to toluene over bimetallic Ni-Fe catalysts
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The catalytic conversion of m-cresol in the presence of H2 has been investigated on SiO2-supported Ni, Fe, and bimetallic Ni-Fe catalysts at 300 °C and atmospheric pressure. Over the monometallic Ni catalyst, the dominant product is 3-methylcyclohexanone while 3-methylcyclohexanol and toluene appear in smaller amounts, even at high conversions. By contrast, on Fe and Ni-Fe bimetallic catalysts, the dominant product is toluene while the hydrogenation products (3-methylcyclohexanone and 3-methylcyclohexanol) are practically negligible in the entire range of conversions. To explain these differences, we have proposed a deoxygenation path that starts with the tautomerization of m-cresol to an unstable ketone intermediate (3-methyl-3,5-cyclohexadienone). The fate of this intermediate is determined by the ability of the catalyst to either hydrogenate the carbonyl group or the ring. The former would mostly occur on Fe and Ni-Fe catalysts that contain an oxophilic metal (Fe), while the latter would occur on Ni, which has a higher affinity for the aromatic ring. Hydrogenation of the carbonyl group produces a very reactive unsaturated alcohol (3-methyl-3,5-cyclohexadienol), which can be easily dehydrated to toluene. This would explain the high selectivity of Fe and Ni-Fe to toluene. By contrast, hydrogenation of the ring would result in 3-methylcyclohexanone, which can be further hydrogenated to 3-methylcyclohexanol. On supports that contain acid sites, which are active for dehydration, the formation of toluene would occur via dehydration of the alcohol and subsequent dehydrogenation. On the catalysts investigated in this work, dehydration of the corresponding alcohol does not occur, so the only path to toluene is via hydrogenation of the carbonyl of the unstable ketone intermediate. In addition, to the products mentioned above, xylenol is also observed in significant yields, which indicate that transalkylation of m-cresol is another reaction path occurring on these catalysts.
- Nie, Lei,De Souza, Priscilla M.,Noronha, Fabio B.,An, Wei,Sooknoi, Tawan,Resasco, Daniel E.
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- Aerobic dehydrogenation of cyclohexanone to phenol catalyzed by Pd(TFA)2/2-dimethylaminopyridine: Evidence for the role of Pd nanoparticles
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We have carried out a mechanistic investigation of aerobic dehydrogenation of cyclohexanones and cyclohexenones to phenols with a Pd(TFA) 2/2-dimethylaminopyridine catalyst system. Numerous experimental methods, including kinetic studies, filtration tests, Hg poisoning experiments, transmission electron microscopy, and dynamic light scattering, provide compelling evidence that the initial PdII catalyst mediates the first dehydrogenation of cyclohexanone to cyclohexenone, after which it evolves into soluble Pd nanoparticles that retain catalytic activity. This nanoparticle formation and stabilization is facilitated by each of the components in the catalytic reaction, including the ligand, TsOH, DMSO, substrate, and cyclohexenone intermediate.
- Pun, Doris,Diao, Tianning,Stahl, Shannon S.
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- Hydrogenation of Halophenols to Cyclohexanols Using Raney Nickel-Aluminium Alloy in Saturated Ba(OH)2 Solution under Mild Conditions
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By use of Raney Nickel-Aluminium alloy in a saturated Ba(OH)2 solution, halophenols are easily hydrogenated at mild temperatures and at atmospheric pressure, giving the corresponding cyclohexanols.
- Tsukinoki, Takehito,Kakinami, Takaaki,Iida, Yukiko,Ueno, Makiko,Ueno, Yoshiko,et al.
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- The multifunctional globin dehaloperoxidase strikes again: Simultaneous peroxidase and peroxygenase mechanisms in the oxidation of EPA pollutants
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The multifunctional catalytic hemoglobin dehaloperoxidase (DHP) from the terebellid polychaete Amphitrite ornata was found to catalyze the H2O2-dependent oxidation of EPA Priority Pollutants (4-Me-o-cresol, 4-Cl-m-cresol and pentachlorophenol) and EPA Toxic Substances Control Act compounds (o-, m-, p-cresol and 4-Cl-o-cresol). Biochemical assays (HPLC/LC-MS) indicated formation of multiple oxidation products, including the corresponding catechol, 2-methylbenzoquinone (2-MeBq), and oligomers with varying degrees of oxidation and/or dehalogenation. Using 4-Br-o-cresol as a representative substrate, labeling studies with 18O confirmed that the O-atom incorporated into the catechol was derived exclusively from H2O2, whereas the O-atom incorporated into 2-MeBq was from H2O, consistent with this single substrate being oxidized by both peroxygenase and peroxidase mechanisms, respectively. Stopped-flow UV–visible spectroscopic studies strongly implicate a role for Compound I in the peroxygenase mechanism leading to catechol formation, and for Compounds I and ES in the peroxidase mechanism that yields the 2-MeBq product. The X-ray crystal structures of DHP bound with 4-F-o-cresol (1.42 ?; PDB 6ONG), 4-Cl-o-cresol (1.50 ?; PDB 6ONK), 4-Br-o-cresol (1.70 ?; PDB 6ONX), 4-NO2-o-cresol (1.80 ?; PDB 6ONZ), o-cresol (1.60 ?; PDB 6OO1), p-cresol (2.10 ?; PDB 6OO6), 4-Me-o-cresol (1.35 ?; PDB 6ONR) and pentachlorophenol (1.80 ?; PDB 6OO8) revealed substrate binding sites in the distal pocket in close proximity to the heme cofactor, consistent with both oxidation mechanisms. The findings establish cresols as a new class of substrate for DHP, demonstrate that multiple oxidation mechanisms may exist for a given substrate, and provide further evidence that different substituents can serve as functional switches between the different activities performed by dehaloperoxidase. More broadly, the results demonstrate the complexities of marine pollution where both microbial and non-microbial systems may play significant roles in the biotransformations of EPA-classified pollutants, and further reinforces that heterocyclic compounds of anthropogenic origin should be considered as environmental stressors of infaunal organisms.
- Ghiladi, Reza A.,Malewschik, Talita,McGuire, Ashlyn H.,de Serrano, Vesna
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- Gold-Catalyzed Proto- and Deuterodeboronation
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A mild gold-catalyzed protodeboronation reaction, which does not require acid or base additives and can be carried out in "green" solvents, is described. As a result, the reaction is very functional-group-tolerant, even to acid- and base-sensitive functional groups, and should allow for the boronic acid group to be used as an effective traceless directing or blocking group. The reaction has also been extended to deuterodeboronations for regiospecific ipso-deuterations of aryls and heteroaryls from the corresponding organoboronic acid. Based on density functional theory calculations, a mechanism is proposed that involves nucleophilic attack of water at boron followed by rate-limiting B-C bond cleavage and facile protonolysis of a Au-σ-phenyl intermediate.
- Barker, Graeme,Webster, Stacey,Johnson, David G.,Curley, Rachel,Andrews, Matthew,Young, Paul C.,MacGregor, Stuart A.,Lee, Ai-Lan
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- Hydroxy- and chloro-dediazoniation of 2- and 3-methylbenzenediazonium tetrafluoroborate in aqueous solution
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We have measured the rates and product yields of dediazoniation of 2- and 3-methylbenzenediazonium tetrafluoroborate in the presence and absence of electrolytes like HCl, NaCl, and CuCl2 using a recently reported methodology that allows simultaneous determination of product concentrations and rates of product formation and, indirectly, loss of starting material. Activation parameters were also obtained: enthalpies of activation are high, and entropies of activation are positive. All results are consistent with a heterolytic mechanism involving the fragmentation of the arenediazonium ion into a very reactive phenyl cation.
- Pazo-Llorente, Roman,Sarabia-Rodriguez, Maria Jose,Bravo-Diaz, Carlos,Gonzalez-Romero, Elisa
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- Cesium carbonate mediated aryl triflate esters' deprotection
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A variety of diversely substituted aryl triflate esters were efficiently deprotected to the parent phenols by exposure to cesium carbonate in toluene. This procedure proved highly compatible with existing functional groups.
- Green, Alice E.,Agouridas, Vangelis,Deniau, Eric
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- Picosecond Electron Transfer from Quantum Dots Enables a General and Efficient Aerobic Oxidation of Boronic Acids
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General visible light-mediated aerobic oxidation of boronic acids is unveiled using CdSe nanocrystal quantum dots (QDs) as the photoredox catalyst. This protocol requires mild reaction conditions and low catalyst loading (down to 10 ppm), and tolerates various functional groups. The resulting phenols and aliphatic alcohols are produced in good to high yield with turnover numbers as high as >62000. The reaction mechanism is probed using ultrafast transient absorption and luminescence spectroscopy. The existence of a rapid 350 ps initial electron transfer followed by a hole transfer is demonstrated.
- Simlandy, Amit Kumar,Bhattacharyya, Biswajit,Pandey, Anshu,Mukherjee, Santanu
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- Pd0-PyPPh2@porous organic polymer: Efficient heterogeneous nanoparticle catalyst for dehydrogenation of 3-methyl-2-cyclohexen-1-one without extra oxidants and hydrogen acceptors
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In this contribution, we have developed an efficient and recyclable porous organic polymer (POP) supported Pd nanoparticle catalyst (Pd°-PyPPh2@POP) for dehydrogenation of 3-methyl-2-cyclohexen-1-one. This heterogeneous catalytic system represents a totally clean process without using any extra oxidant and hydrogen acceptors. The SEM-EDS mapping images of the Pd°-PyPPh2@POP catalyst reveal the highly uniformly dispersed character of C, Pd, P and N elements. The coordination bonds between Pd nanoparticle and exposed P atom as well as N atom on the surface of PyPPh2@POP polymer are confirmed by means of solid-state 31P NMR and XPS. Importantly, both P atom and pyridyl ring on the PyPPh2@POP polymer are themselves used as solid base over the Pd°-PyPPh2@POP catalyst, leading to a catalytic conversion of 88.2% even without the employment of inorganic base additives (K2CO3). Our results have provided a strategy for designing highly active bifunctional POP supported nanoparticle catalysts.
- Chen, Xingkun,Wang, Wenlong,Zhu, Hejun,Yang, Wenshao,Ding, Yunjie
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- Graphite encapsulated molybdenum carbide core/shell nanocomposite for highly selective conversion of guaiacol to phenolic compounds in methanol
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Graphite encapsulated molybdenum carbides (Mo2C@C) were synthesized via the hydrothermal carbonization of a solution of glucose and ammonium molybdate followed by temperature programmed reduction. Characterization and structural analyses revealed that the synthesized Mo2C@C nanoparticles had a molybdenum core/carbon shell structure with a particle size ranging from 50 nm to 100 nm and a core size range of 5–45 nm. The catalytic performance of the graphite encapsulated molybdenum carbides was evaluated on conversion of guaiacol to phenolic compounds in methanol. At 340 °C under 2.8 MPa hydrogen pressure, a 76.3% guaiacol conversion was obtained with selectivities of 68.6% for phenol and 93.5% for phenolic compounds. Thus, Mo2C@C showed high selectivity for phenolic compounds in methanol.
- Li, Rui,Shahbazi, Abolghasem,Wang, Lijun,Zhang, Bo,Hung, Albert M.,Dayton, David C.
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- Imidazolium-urea low transition temperature mixtures for the UHP-promoted oxidation of boron compounds
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Different carboxy-functionalized imidazolium salts have been considered as components of low transition temperature mixtures (LTTMs) in combination with urea. Among them, a novel LTTM based on 1-(methoxycarbonyl)methyl-3-methylimidazolium chloride and urea has been prepared and characterized by differential scanning calorimetry throughout its entire composition range. This LTTM has been employed for the oxidation of boron reagents using urea-hydrogen peroxide adduct (UHP) as the oxidizer, thus avoiding the use of aqueous H2O2, which is dangerous to handle. This metal-free protocol affords the corresponding alcohols in good to quantitative yields in up to 5 mmol scale without the need of further purification. The broad composition range of the LTTM allows for the reaction to be carried out up to three consecutive times with a single imidazolium salt loading offering remarkable sustainability with an E-factor of 7.9, which can be reduced to 3.2 by the threefold reuse of the system.
- Martos, Mario,Pastor, Isidro M.
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- Highly selective demethylation of anisole to phenol over H4Nb2O7modified MoS2catalyst
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Hydrogenolysis of lignin to obtain value-added phenolic chemicals is an important approach for its comprehensive utilization. Herein, H4Nb2O7modified MoS2catalyst with short slabs and narrow stacking degree was successfully synthesized by the one step hydrothermal method and used in the selective demethylation of anisole to phenol. The MoS2-H4Nb2O7-160 catalyst exhibited the best activity with 97.7% conversion of anisole and 98.0% selectivity of phenol under 3 MPa H2pressure at 270 °C for 4 h, which has been rarely reported on anisole transformation over heterogeneous catalysts so far. The characterizations results demonstrated that the H4Nb2O7modification reduced the slab length and stacking degree of MoS2during the hydrothermal process and enhanced the acidity property therefore improved the cleavage ability of CArO-CH3bond. This study provides a new scheme for the activity enhancement of MoS2in lignin demethylation, laying a foundation on the improvement of lignin utilization and the development of renewable energy strategy.
- Ji, Na,Wang, Zhenjiao,Diao, Xinyong,Jia, Zhichao,Li, Tingting,Zhao, Yujun,Liu, Qingling,Lu, Xuebin,Ma, Degang,Song, Chunfeng
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p. 800 - 809
(2021/02/26)
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- Visible light-induced photodeoxygenation of polycyclic selenophene Se-oxides
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Photodeoxygenation of dibenzothiophene S-oxide (DBTO) is believed to produce ground-state atomic oxygen [O(3P)] in solution. Compared with other reactive oxygen species (ROS), O(3P) is a unique oxidant as it is potent and selective. Derivatives of DBTO have been used as O(3P)-precursors to oxidize variety of molecules, including plasmid DNA, proteins, lipids, thiols, and other small organic molecules. Unfortunately, the photodeoxygenation of DBTO requires ultraviolet irradiation, which is not an ideal wavelength range for biological systems, and has a low quantum yield of approximately 0.003. In this work, benzo[b]naphtho[1,2-d]selenophene Se-oxide, benzo[b]naphtho[2,1-d]selenophene Se-oxide, dinaphtho[2,3-b:2’,3’-d]selenophene Se-oxide, and perylo[1,12-b,c,d]selenophene Se-oxide were synthesized, and their ability to utilize visible light for generating O(3P) was interrogated. Benzo[b]naphtho[1,2-d]selenophene Se-oxide produces O(3P) upon irradiation centered at 420 nm. Additionally, benzo[b]naphtho[1,2-d]selenophene Se-oxide, benzo[b]naphtho[2,1-d]selenophene Se-oxide, and dinaphtho[2,3-b:2’,3’-d]selenophene Se-oxide produce O(3P) when irradiated with UVA light and have quantum yields of photodeoxygenation ranging from 0.009 to 0.33. This work increases the utility of photodeoxygenation by extending the range of wavelengths that can be used to generate O(3P) in solution.
- Chintala, Satyanarayana M.,Throgmorton, John C.,Maness, Peter F.,McCulla, Ryan D.
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- Selective hydroxylation of aryl iodides to produce phenols under mild conditions using a supported copper catalyst
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Owing to the high activity and low-cost, copper-based catalysts are promising candidates for transforming aromatic halides to yield phenols. In this work, we report the selective hydroxylation of aromatic iodides to produce phenols using an atomically dispersed copper catalyst (Cu-ZnO-ZrO2) under mild reaction conditions. The reactions were conducted without the use of additional organic ligands, and the protection of an inert atmosphere environment is not required. The catalyst can be easily prepared, scalable, and is very efficient for a wide range of substrates. The catalytic reactions can be carried out with only 1.24 mol% Cu loading, which shows great potential in mass production.
- Auni, Anika,Ding, Guodong,Hao, Leiduan,Li, Tao,Li, Xiaoyu,Xu, Haiping,Zhang, Qiang
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p. 25348 - 25353
(2021/08/03)
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- Photocatalytic synthesis of phenols mediated by visible light using KI as catalyst
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A transition-metal-free hydroxylation of iodoarenes to afford substituted phenols is described. The reaction is promoted by KI under white LED light irradiation and uses atmospheric oxygen as oxidant. By the use of triethylamine as base and solvent, the corresponding phenols are obtained in moderate to good yields. Mechanistic studies suggest that KI and catalysis synergistically promote the cleavage of C-I bond to form free aryl radicals.
- Huiqin, Wei,Wu, Mei
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supporting information
(2021/11/30)
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- Electrochemical-induced hydroxylation of aryl halides in the presence of Et3N in water
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A thorough study of mild and environmentally friendly electrochemical-induced hydroxylation of aryl halides without a catalyst is presented. The best protocol consists of hydroxylation of different aryl iodides and aryl bromides by water solution in the presence of Et3N under air, affording the target phenols in good isolated yields. Moreover, aryl chlorides were successfully employed as substrates. This methodology also provides a direct pathway for the formation of deoxyphomalone, which displayed a significant anti-proliferation effect.
- Ke, Fang,Lin, Chen,Lin, Mei,Long, Hua,Wu, Mei,Yang, Li,Zhuang, Qinglong
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supporting information
p. 6417 - 6421
(2021/08/03)
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- A copper nitride catalyst for the efficient hydroxylation of aryl halides under ligand-free conditions
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Copper nitride (Cu3N) was used as a heterogeneous catalyst for the hydroxylation of aryl halides under ligand-free conditions. The cubic Cu3N nanoparticles showed high catalytic activity, comparable to those of conventional Cu catalysts with nitrogen ligands, demonstrating that the nitrogen atoms in Cu3N act as functional ligands that promote hydroxylation.
- Mitsudome, Takato,Mizugaki, Tomoo,Xu, Hang,Yamaguchi, Sho
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supporting information
p. 6593 - 6597
(2021/08/10)
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- Isotruxene-based porous polymers as efficient and recyclable photocatalysts for visible-light induced metal-free oxidative organic transformations
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Two new isotruxene-based porous polymers were prepared and demonstrated to be highly efficient, metal-free heterogeneous photocatalysts for oxidative transformations using air as the mild oxidant under visible-light irradiation. Both catalysts show excellent recyclability. In addition, the reactions can be performed in water, further indicating the greenness of this method. This journal is
- Zhang, Haowen,Zhang, Xiao,Zheng, Ying,Zhou, Cen
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supporting information
p. 8878 - 8885
(2021/11/27)
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- Catalyst-free rapid conversion of arylboronic acids to phenols under green condition
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A catalyst-free and solvent-free method for the oxidative hydroxylation of aryl boronic acids to corresponding phenols with hydrogen peroxide as the oxidizing agent was developed. The reactions could be performed under green condition at room temperature within very short reaction time. 99% yield of phenol could be achieved in only 1 min. A series of different arenes substituted aryl boronic acids were further carried out in the hydroxylation reaction with excellent yield. It was worth nothing that the reaction could completed within 1 min in all cases in the presence of ethanol as co-solvent.
- Dong, Zhenhua,Liu, Mengmeng,Pan, Hongguo
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- Coordination Polymers as a Functional Material for the Selective Molecular Recognition of Nitroaromatics and ipso-Hydroxylation of Arylboronic Acids
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We report the synthesis and structural characterization of two coordination polymers (CPs), namely; [{Zn(L)(DMF)4} ? 2BF4]α (1) and [{Cd(L)2(Cl)2} ? 2H2O]α (2) (where L=N2,N6-di(pyridin-4-yl)naphthalene-2,6-dicarboxamide). Crystal packing of 1 reveals the existence of channels running along the b- and c-axis filled by the ligated DMF and lattice anions, respectively. Whereas, crystal packing of 2 reveals that the metallacycles of each 1D chain are intercalating into the groove of adjacent metallacycles resulting in the stacking of 1D loop-chains to form a sheet-like architecture. In addition, both 1 and 2 were exploited as multifunctional materials for the detection of nitroaromatic compounds (NACs) as well as a catalyst in the ipso-hydroxylation of aryl/heteroarylboronic acids. Remarkably, 1 and 2 showed high fluorescence stability in an aqueous medium and displayed a maximum 88% and 97% quenching efficiency for 4-NPH, respectively among all the investigated NACs. The mechanistic investigation of NACs recognition suggested that the fluorescence quenching occurred via electron as well as energy transfer process. Furthermore, the ipso-hydroxylation of aryl/heteroarylboronic acids in presence of 1 and 2 gave up to 99% desired product yield within 15 min in our established protocol. In both cases, 1 and 2 are recyclable upto five cycles without any significant loss in their efficiency.
- Bhasin, K. K.,Husain, Ahmad,Kumar, Girijesh,Rani, Pooja
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- Blacklight-Induced Hydroxylation of Arylboronic Acids Leading to Hydroxyarenes Using Molecular Oxygen and Tetrabutylammonium Borohydride
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A new simple protocol for the conversion of arylboronic acids to hydroxyarenes was achieved using molecular oxygen in the presence of tetrabutylammonium borohydride under blacklight irradiation (360 nm). A radical chain mechanism in which a superoxide ion (O2?.) plays a key role is proposed.
- Kawamoto, Takuji,Ryu, Ilhyong
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- Method for hydrolyzing diarylether compound to generate aryl phenol compound
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The invention discloses a method for hydrolyzing a diarylether compound to generate an arylphenol compound. According to the method, visible light is utilized to excite a photosensitizer for catalysis. In a reaction solvent, the raw material in the formula (1) breaks a C (sp2)-O bond under the auxiliary action of acid, and hydrolysis is performed to obtain the bimolecular aryl phenol compounds in the formula (3) and the formula (4). The method can catalyze the reaction at room temperature, is green and environment-friendly, and is easy to operate; the universality is wide, the reaction yield is relatively high, and the tolerance of functional groups is strong; the synthesis method not only can realize small-scale hydrolysis conversion of various diarylether compounds, but also can realize hydrolysis of herbicidal ether, triclosan and a lignin template substrate, and even can realize large-scale hydrolysis of triclosan and the lignin template substrate to realize gram-level degradation. A new strategy is provided for recovering phenol derivatives through lignin hydrolysis, degrading pesticides and purifying wastewater containing a degerming agent or herbicide. The method has wide application prospect and use value.
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Paragraph 0074-0077
(2021/09/29)
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- Eco-friendly preparation of ultrathin biomass-derived Ni3S2-doped carbon nanosheets for selective hydrogenolysis of lignin model compounds in the absence of hydrogen
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Lignin is an abundant source of aromatics, and the depolymerization of lignin provides significant potential for producing high-value chemicals. Selective hydrogenolysis of the C-O ether bond in lignin is an important strategy for the production of fuels and chemical feedstocks. In our study, catalytic hydrogenolysis of lignin model compounds (β-O-4, α-O-4 and 4-O-5 model compounds) over Ni3S2-CS catalysts was investigated. Hence, an array of 2D carbon nanostructure Ni3S2-CSs-X-Yderived catalysts were produced using different compositions at different temperatures (X= 0 mg, 0.2 mg, 0.4 mg, 0.6 mg, and 0.8 mg; Y = 600 °C, 700 °C, 800 °C, and 900 °C) were prepared and applied for hydrogenolysis of lignin model compounds and depolymerization of alkaline lignin. The highest conversion of lignin model compounds (β-O-4 model compound) was up to 100% and the yield of the obtained corresponding ethylbenzene and phenol could achieve 92% and 86%, respectively, over the optimal Ni3S2-CSs-0.4-700 catalyst in iPrOH at 260 °C without external H2. The 2D carbon nanostructure catalysts performed a good dispersion on the surface of the carbon nanosheets, which facilitated the cleavage of the lignin ether bonds. The physicochemical characterization studies were carried out by means of XRD, SEM, TEM, H2-TPR, NH3-TPD, Raman and XPS analyses. Based on the optimal reaction conditions (260 °C, 4 h, 2.0 MPa N2), various model compounds (β-O-4, α-O-4 and 4-O-5 model compounds) could also be effectively hydrotreated to produce the corresponding aromatic products. Furthermore, the optimal Ni3S2-CSs-0.4-700 catalyst could be carried out in the next five consecutive cycle experiments with a slight decrease in the transformation of lignin model compounds.
- Chen, Changzhou,Jiang, Jianchun,Li, Jing,Liu, Peng,Wu, Dichao,Xia, Haihong,Zhou, Minghao
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p. 3090 - 3103
(2021/05/07)
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- CATALYTIC FUNNELING OF PHENOLICS
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In general, present invention concerns an integrated wood-to-xylochemicals biorefinery, enabling production of renewable phenol, phenolic oligomers, propylene, and carbohydrate pulp from lignocellulosic biomass.
- -
-
Paragraph 0034; 0089-0090; 0167-0168
(2021/04/30)
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- Reduced Amino Acid Schiff Base-Iron(III) Complexes Catalyzing Oxidation of Cyclohexane with Hydrogen Peroxide
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The reduced amino acid Schiff base ligands have been prepared and were coordinated with ferric chloride to generate the iron(III) complexes. The ligands and complexes have been characterized using FT-IR, UV-vis, elemental analysis, ICP-AES analysis, mass spectra etc. After the structural characterization, these complexes were applied for the oxidation of cyclohexane using hydrogen peroxide as the oxidant under mild conditions. The activity tests showed that the L-phenylalanine-derived reduced Schiff base iron(III) complex(Ph?FeCl) afforded the highest yield of cyclohexanol and cyclohexanone(total yield up to 23.2 %). Notably, the Ph?FeCl complex catalyzes the reaction via a heterogeneous approach, allowing the complex to be separated and recycled conveniently after the oxidation reaction. Besides, the Ph?FeCl catalyst can also be extended for the selective oxidation of other alkanes and aromatics into alcohols, ketones and phenols etc. Finally, the reaction mechanism of cyclohexane oxidation on the iron(III) complex was proposed as well by the free radical inhibitors and EPR study of active intermediates.
- Zheng, Anna,Zhou, Qingqing,Ding, Bingjie,Li, Difan,Zhang, Tong,Hou, Zhenshan
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p. 3385 - 3395
(2021/08/23)
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- Catalytic SNAr Hydroxylation and Alkoxylation of Aryl Fluorides
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Nucleophilic aromatic substitution (SNAr) is a powerful strategy for incorporating a heteroatom into an aromatic ring by displacement of a leaving group with a nucleophile, but this method is limited to electron-deficient arenes. We have now established a reliable method for accessing phenols and phenyl alkyl ethers via catalytic SNAr reactions. The method is applicable to a broad array of electron-rich and neutral aryl fluorides, which are inert under classical SNAr conditions. Although the mechanism of SNAr reactions involving metal arene complexes is hypothesized to involve a stepwise pathway (addition followed by elimination), experimental data that support this hypothesis is still under exploration. Mechanistic studies and DFT calculations suggest either a stepwise or stepwise-like energy profile. Notably, we isolated a rhodium η5-cyclohexadienyl complex intermediate with an sp3-hybridized carbon bearing both a nucleophile and a leaving group.
- Kang, Qi-Kai,Li, Ke,Li, Yuntong,Lin, Yunzhi,Shi, Hang,Xu, Lun
-
supporting information
p. 20391 - 20399
(2021/08/13)
-
- Reaction of hydroxyl radical with arenes in solution—On the importance of benzylic hydrogen abstraction
-
The regioselectivity of hydroxyl radical reactions with alkylarenes was investigated using a nuclear magnetic resonance (NMR)-based methodology capable of trapping and quantifying addition and hydrogen abstraction products of the initial elementary step of the oxidation process. Abstraction products are relatively minor components of the product mixtures (15–30 mol%), depending on the magnitude of the overall rate coefficient and the number of available hydrogens. The relative reactivity of addition at a given position on the ring depends on its relation to the methyl substituents on the hydrocarbons under study. The reactivity enhancements for disubstituted and trisubstituted rings are approximately additive under the conditions of this study.
- Waggoner, Abygail R.,Abdulrahman, Yahya,Iverson, Alexis J.,Gibson, Ethan P.,Buckles, Mark A.,Poole, James S.
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-
- Role of Catalyst Support's Physicochemical Properties on Catalytic Transfer Hydrogenation over Palladium Catalysts
-
Catalytic transfer hydrogenation (CTH) is a promising reaction for valorisation of bio-based feedstocks via hydrogenation without needing to use H2. Unlike standard hydrogenation, CTH occurs via dehydrogenation (DHD) of a hydrogen donor (H-donor) and hydrogenation (HYD) of a substrate. Therefore, the “ideal” CTH catalyst must balance the catalysis of both reactions to maximize the hydrogen transfer between H-donor and substrate with minimal H2 loss to gas (high atom efficiency). Additionally, the H-donor must be highly stable to prevent secondary reactions with the substrate. Herein we study the impact of the catalyst's properties on CTH of guaiacol using bicyclohexyl, a liquid organic hydrogen carrier, as a H-donor. The reaction was promoted by palladium dispersed on three typical support materials (γ-Al2O3, MgO, and SiO2). The performance of these catalysts in the conversion of bicyclohexyl and guaiacol was evaluated, allowing to estimate the H-transfer efficiency, as well as the potential for recycling the spent H-donor (bicyclohexyl). The apparent activation energies for DHD of bicyclohexyl and HYD of guaiacol revealed that slow DHD combined with fast HYD, as is the case with Pd/MgO, favours hydrogen transfer efficiency and selectivity towards hydrogenated products. In addition, an investigation of the DHD of bicyclohexyl and HYD of guaiacol independently showed that the affinity between the organic molecules and the support significantly impacts CTH. Indeed, Pd/SiO2 was highly active for both reactions individually and almost inactive for CTH. Consequently, these findings highlight the importance of the interaction between solvent-substrate-support in designing catalysts for transfer hydrogenation.
- Batalha, Nuno,Fraga, Gabriel,Hasan, M. D.,Konarova, Muxina,Laycock, Bronwyn,Pratt, Steven,Santos, Mirella S.
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p. 5191 - 5202
(2021/10/29)
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- Metal-organic frameworks containing nitrogen-donor ligands for efficient catalytic organic transformations
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Metal-organic framework (MOFs) compositions based on nitrogen donor-based organic bridging ligands, including ligands based on 1,3-diketimine (NacNac), bipyridines and salicylaldimine, were synthesized and then post-synthetically metalated with metal precursors, such as complexes of first row transition metals. Metal complexes of the organic bridging ligands could also be directly incorporated into the MOFs. The MOFs provide a versatile family of recyclable and reusable single-site solid catalysts for catalyzing a variety of asymmetric organic transformations. The solid catalysts can also be integrated into a flow reactor or a supercritical fluid reactor.
- -
-
Page/Page column 36-37
(2020/06/03)
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- Method for preparing alcohol and phenol through aerobic hydroxylation reaction of boric acid derivative in absence of photocatalyst
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The invention discloses a method for preparing alcohol and phenol through aerobic hydroxylation reaction of a boric acid derivative in the absence of a photocatalyst, wherein the boric acid derivativeis aryl boronic acid or alkyl boronic acid, and the corresponding target compounds are respectively a phenol-based compound and an alcohol-based compound. According to the method, by using a boric acid derivative as a reaction substrate, an additive is added under a solvent condition, and a hydroxylation reaction is performed under aerobic and illumination conditions to obtain a corresponding target compound. According to the invention, the new strategy is provided for the synthesis of phenols through aerobic hydroxylation of aryl boronic acid without a photocatalyst; the catalyst-free aerobic hydroxylation method for photocatalysis of aryl boronic acid or alkyl boronic acid by using triethylamine as an additive is firstly disclosed; and the new method has advantages of photocatalyst-freecondition, wide substrate range and good functional group compatibility.
- -
-
Paragraph 0025-0028; 0030-0032
(2020/01/25)
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- Method for synthesizing phenol or derivative thereof in aqueous phase by photocatalytic one-pot method
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The invention discloses a method for synthesizing phenol or a derivative thereof in an aqueous phase by a photocatalytic one-pot method. The method comprises the following steps: by taking a compoundaryl halide shown in formula (I) as a raw material and water as a solvent, adding a catalyst and an auxiliary agent, and carrying out reacting under the conditions of alkali and visible light to obtain the phenol or the derivative (II) thereof. Compared with the prior art, the method is applicable to a large number of functional groups, high in yield, few in byproducts, simple and safe to operate,low in cost and environmentally friendly, wherein R is selected from substituted or non-substituted phenyl, pyridyl, quinolyl or pyrimidinyl; X is selected from halogen; the substituted phenyl is substituted by C1-C4 alkyl, C1-C4 alkoxy, hydroxyl, halogen, cyano, aldehyde group, nitro, amino, acetyl or carboxyl; and the substituted pyridyl, quinolyl or pyrimidinyl is pyridyl, quinolyl or pyrimidinyl substituted by C1-C4 alkyl.
- -
-
Paragraph 0032-0033; 0070-0071; 0085-0106
(2020/12/08)
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- Ionic liquid-stabilized vanadium oxo-clusters catalyzing alkane oxidation by regulating oligovanadates
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Alkane oxidation under mild conditions occupies an important position in the chemical industry. Herein, we have designed a novel class of ionic liquid ([TBA][Pic])-stabilized vanadium oxo-clusters (TBA = tetrabutylammonium; Pic = picolinate ions), in which the molar ratio of the IL to V atoms can be tuned facilely to obtain V-OC?IL-0.5, V-OC?IL-1 and V-OC?IL-2, respectively. The as-synthesized vanadium oxo-clusters have been characterized by elemental analysis, FT-IR, UV-vis, XRD, TGA, EPR, NMR and MS. These vanadium oxo-clusters were catalytically active for catalyzing the oxidation of cyclohexane with H2O2 as an oxidant. In particular, the oxo-cluster V-OC?IL-1 (where IL/V is 1.0) can provide an approximately 30% total yield of KA oil (cyclohexanol and cyclohexanone) without adding any co-catalyst at 50 °C within 1.0 h. Moreover, the present vanadium oxo-cluster was recyclable owing to the modification of the IL and it can also be extended to the oxidation of the sp2 hybrid aromatic ring. The further characterization results demonstrated that the oligovanadate anions were strongly dependent on the molar ratio of the IL to V atoms. The vanadium oxo-clusters with the appropriate molar ratio of IL/V could exist in the form of a trimer and a dimer due to the presence of the TBA cation and the coordination of picolinate. Notably, the oligovanadate anions are highly active species for the C-H oxidation but the mononuclear vanadate afforded a very poor activity according to the activity assessment and the identification of vanadium species from the 51V NMR spectra and MS spectra. The annihilation reaction of free radicals and EPR characterization suggested that the vanadium oxo-clusters operated via a mechanism of the HO radical in the oxidation reaction.
- Ding, Bingjie,Gong, Xueqing,Hou, Zhenshan,Li, Difan,Yao, Yefeng,Zhang, Ran,Zheng, Anna,Zhou, Qingqing
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p. 7601 - 7612
(2020/11/27)
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- Trinuclear Mn2+/Zn2+based microporous coordination polymers as efficient catalysts foripso-hydroxylation of boronic acids
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Two microporous coordination polymers based on hourglass trinuclear building units, [Mn3(bpdc)3(bpy)]·2DMF and [Zn3(bpdc)3(bpy)]·2DMF·4H2O (bpdc = 4,4′-biphenyl dicarboxylic acid, bpy = 4,4′-bipyridine), have been synthesized under solvothermal conditions employing DMF as the solvent. Each structure consists of two crystallographically distinct M2+(M1 and M2) centers that are connectedviacarboxylate bridges from six bpdc ligands, generating a trinuclear metal cluster, [M3(bpdc)3(bpy)]. Cluster representation of the structure resulted in an interpenetrated net of rarehextopological type. Catalytic activities of the CPs have been assessed for the oxidative hydroxylation of phenylboronic acids (PBAs) using aqueous hydrogen peroxide (H2O2). Various substituted aryl/hetero-arylboronic acids RB(OH)2[R = phenyl, 2,4-difluorophenyl, 4-aminophenyl, 2-thiopheneetc.] underwentipso-hydroxylation smoothly at room temperature to generate the corresponding phenols in excellent yields. The main advantages of this protocol are the aqueous medium reaction, heterogeneous catalytic system, and short reaction time with excellent yield.
- Bora, Sanchay J.,Dutta, Anurag,Goswami, Shyam,Guha, Ankur K.,Paul, Rima,Thakur, Ashim J.
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p. 5454 - 5462
(2020/05/16)
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- Aerobic photooxidative hydroxylation of boronic acids catalyzed by anthraquinone-containing polymeric photosensitizer
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We report herein the synthesis of a polymeric photosensitizer and its application in aerobic photooxidative hydroxylation of boronic acids. The polymeric photosensitizer was synthesized by the condensation of anthraquinone-2-carbonyl chloride (AQ-2-COCl) with poly (2-hydroxyethyl methacrylate) (PHEMA). The photo-oxidative hydroxylation of boronic acids using anthraquinone-containing-poly (2-hydroxyethyl methacrylate) (AQ-PHEMA) was then explored and shown to exhibit high efficiency and broad scope. Moreover, AQ-PHEMA could be easily recovered and reused for more than 20 times without significant loss of the catalytic activity.
- Chen, Yang,Ding, Aishun,Hu, Jianhua
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p. 7927 - 7932
(2020/03/11)
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- An efficient base and H2O2 free protocol for the synthesis of phenols in water and oxygen using spinel CuFe2O4 magnetic nanoparticles
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An efficient base and H2O2 free protocol was used for the synthesis of phenols from boronic acids using biogenic CuFe2O4 magnetic nanoparticles as catalyst at room temperature in water and oxygen. The catalyst was prepared using the flowers of Lantana camara. The size of the nanoparticles was 4.27 nm. Base free and ligand free protocol, less time, excellent yields, room temperature, biogenic synthesis of the catalyst, use of O2 as an environmentally friendly oxidant are the advantages of the present protocol. The recyclability of the catalyst was for 5 cycles without loss of magnetic property or catalytic activity.
- Chutia, Rituparna,Chetia, Bolin
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p. 1925 - 1936
(2020/08/13)
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- Quaternary ammonium hydroxide-functionalized g-C3N4 catalyst for aerobic hydroxylation of arylboronic acids to phenols
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A new and efficient metal-free approach toward the synthesis of phenols via an aerobic hydroxylation of arylboronic acids by using a novel quaternary ammonium hydroxide g-C3N4 catalyst has been described. The functionalized quaternary ammonium hydroxide (g-C3N4-OH) has been prepared from graphitic carbon nitride (g-C3N4) scaffold by converting the residual –NH2 and –NH groups to quaternary methyl ammonium iodide by performing a methylation reaction with methyl iodide followed by ion-exchange with 0.1 N KOH or anion exchange resin Amberlyst A26 (OH- form) by post-synthetic modification. The resultant g-C3N4-OH was characterized by XRD, FTIR, field-emission scanning electron microscope (FESEM), high-resolution transmission electron microscope (HRTEM), N2 adsorption/desorption isotherms, and acid–base titration. Tested as solid-base catalysts, the g-C3N4-OH showed excellent catalytic activity in the aerobic hydroxylation reaction by converting a variety of arylboronic acids to the corresponding phenols in high yields. More importantly, the g-C3N4-OH solid-base has been successfully reused four times with the minor loss of initial catalytic activity (10.5percent).
- Muhammad, Ibrahim,Mannathan, Subramaniyan,Sasidharan, Manickam
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p. 1470 - 1476
(2020/07/13)
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- Helical Carbenium Ion: A Versatile Organic Photoredox Catalyst for Red-Light-Mediated Reactions
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Red light has the advantages of low energy, less health risks, and high penetration depth through various media. Herein, a helical carbenium ion (N,N′-di-n-propyl-1,13-dimethoxyquinacridinium (nPr-DMQA+) tetrafluoroborate) has been used as an organic photoredox catalyst for photoreductions and photooxidations in the presence of red light (λmax = 640 nm). It has catalyzed red-light-mediated dual transition-metal/photo-redox-catalyzed C-H arylation and intermolecular atom-transfer radical addition through oxidative quenching. Moreover, its potential in photooxidation catalysis has also been demonstrated by successful applications in red-light-induced aerobic oxidative hydroxylation of arylboronic acids and benzylic C(sp3)-H oxygenation through reductive quenching. Thus, a versatile organic photoredox catalyst (helical carbenium ion) for red-light-mediated photoredox reactions has been developed.
- Mei, Liangyong,Veleta, José M.,Gianetti, Thomas L.
-
supporting information
p. 12056 - 12061
(2020/08/07)
-
- Visible-light-promoted aerobic oxidative hydroxylation of arylboronic acids in water by hydrophilic organic semiconductor
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A green and sustainable catalytic system was developed based on perylenediimide (PDI) organic semiconductor for the aerobic oxidative hydroxylation of arylboronic acids in aqueous solution with visible light. By using PDI-SN, a hydrophilic organic semiconductor, which can activate oxygen to produce superoxide radicals in aqueous solution, this reaction proceeds under ambient conditions: water as the solvent and air as the oxidant, giving various phenols as products with high yields. In contrast to methods using organic solvents, this novel process has the potential of green industrial application.
- Yu, Kunyi,Zhang, Hanjie,Sheng, Yuqiang,Zhu, Yongfa
-
supporting information
(2020/06/23)
-
- Transition-Metal-Free C(sp2)–C(sp2) Cross-Coupling of Diazo Quinones with Catechol Boronic Esters
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A transition-metal-free C(sp2)?C(sp2) bond formation reaction by the cross-coupling of diazo quinones with catechol boronic esters was developed. With this protocol, a variety of biaryls and alkenyl phenols were obtained in good to high yields under mild conditions. The reaction tolerates various functionalities and is applicable to the derivatization of pharmaceuticals and natural products. The synthetic utility of the method was demonstrated by the short synthesis of multi-substituted triphenylenes and three bioactive natural products, honokiol, moracin M, and stemofuran A. Mechanistic studies and density functional theory (DFT) calculations revealed that the reaction involves attack of the boronic ester by a singlet quinone carbene followed by a 1,2-rearrangement through a stepwise mechanism.
- Che, Chi-Ming,Wu, Kai,Wu, Liang-Liang,Zhou, Cong-Ying
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p. 16202 - 16208
(2020/07/17)
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- Nanoporous Na+-montmorillonite perchloric acid as an efficient and recyclable catalyst for the chemoselective protection of hydroxyl groups
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Nanoporous Na+-montmorillonite perchloric acid as a novel heterogeneous reusable solid acid catalyst was easily prepared by treatment of Na+-montmorillonite as a cheap and commercially available support with perchloric acid. The catalyst was characterized using a variety of techniques including X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), energy dispersive X-ray spectroscopy (EDX), pH analysis and determination of the Hammett acidity function. The prepared reagent showed excellent catalytic activity for the chemoselective conversion of alcohols and phenols to their corresponding trimethylsilyl ethers with 1,1,1,3,3,3-hexamethyldisilazane (HMDS) at room temperature. Deprotection of the resulting trimethylsilyl ethers can also be carried out using the same catalyst in ethanol. All reactions were performed under mild and completely heterogeneous reaction conditions in good to excellent yields. The notable advantages of this protocol are: short reaction times, high yields, availability and low cost of the reagent, easy work-up procedure and the reusability of the catalyst during a simple filtration.
- Mashhadinezhad, Maryam,Shirini, Farhad,Mamaghani, Manouchehr
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p. 2099 - 2107
(2019/01/03)
-
- Regioselectivity of Hydroxyl Radical Reactions with Arenes in Nonaqueous Solutions
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The regioselectivity of hydroxyl radical addition to arenes was studied using a novel analytical method capable of trapping radicals formed after the first elementary step of reaction, without alteration of the product distributions by secondary oxidation processes. Product analyses of these reactions indicate a preference for o- over p-substitution for electron donating groups, with both favored over m-addition. The observed distributions are qualitatively similar to those observed for the addition of other carbon-centered radicals, although the magnitude of the regioselectivity observed is greater for hydroxyl. The data, reproduced by high accuracy CBS-QB3 computational methods, indicate that both polar and radical stabilization effects play a role in the observed regioselectivities. The application and potential limitations of the analytical method used are discussed.
- Moores, Lee C.,Kaur, Devinder,Smith, Mathew D.,Poole, James S.
-
supporting information
p. 3260 - 3269
(2019/03/11)
-
- Photodeoxygenation of phenanthro[4,5-bcd]thiophene S-oxide, triphenyleno[1,12-bcd]thiophene S-oxide and perylo[1,12-bcd]thiophene S-oxide
-
Sulfoxides, upon irradiation with ultraviolet (UV) light undergo α-cleavage, hydrogen abstraction, photodeoxygenation, bimolecular photoreduction, and stereo-mutation. The UV irradiation of dibenzothiophene S-oxide (DBTO) yields dibenzothiophene (DBT) as a major product along with ground-state atomic oxygen [O(3P)]. This is a common method for generating O(3P) in solution. The low quantum yield of photodeoxygenation and the requirement of UVA light are drawbacks of using this method. The sulfoxides benzo[b]naphtho-[1,2,d]thiophene S-oxide, benzo[b]naphtho [2,1,d]thiophene S-oxide, benzo[b] phenanthro[9,10-d]thiophene S-oxide, dinaphtho- [2,1-b:1’,2’-d]thiophene S-oxide, and dinaphtho[1,2-b:2’,1’-d]thiophene S-oxide have shown to deoxygenate up to three times faster than DBTO upon UVA irradiation; however, the photodeoxygenation of these sulfoxides does not appear to be limited to the production of O(3P). In this work, phenanthro[4,5-bcd]thiophene S-oxide, triphenyleno[1,12-bcd]thiophene-S-oxide, and perylo[1,12-bcd]thiophene-S-oxide were synthesized and their photodeoxygenation was studied. Phenanthro[4,5-bcd]thiophene-S-oxide, triphenyleno[1,12-bcd]thiophene-S-oxide, and perylo[1,12-bcd]thiophene-S-oxide deoxygenated upon UVA irradiation. However, the common intermediate experiments did not conclusively identify the photodeoxygenation mechanism of these sulfoxides.
- Chintala, Satyanarayana M.,Petroff II, John T.,Barnes, Andrew,McCulla, Ryan D.
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p. 503 - 515
(2019/05/29)
-
- Photoinduced Hydroxylation of Organic Halides under Mild Conditions
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Presented in this paper is photoinduced hydroxylation of organic halides, providing a mild access to a range of functionalized phenols and aliphatic alcohols. These reactions generally proceed under mild reaction conditions with no need for a photocatalyst or a strong base and show a wide substrate scope as well as excellent functional group tolerance. This work highlights the unique role of NaI that allows a challenging transformation to proceed under mild reaction conditions.
- Cai, Yue-Ming,Xu, Yu-Ting,Zhang, Xin,Gao, Wen-Xia,Huang, Xiao-Bo,Zhou, Yun-Bing,Liu, Miao-Chang,Wu, Hua-Yue
-
supporting information
p. 8479 - 8484
(2019/10/16)
-
- Versatile catalysis of “natural extract”: oxidation of sulfides and alcohols and ipso-hydroxylation of arylboronic acids
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Abstract: In the present work, we have described the versatile applications of naturally available inexpensive citrous lemon juice as biocatalyst for controlled oxidation of sulfides and alcohols and ipso-hydroxylation of arylboronic acids using 30% H2O2 as a green oxidant. A series of structurally divergent sulfides and benzyl alcohols were oxidized to their corresponding sulfoxides and aldehydes, respectively, with good-to-excellent yields. Similarly, aryl and heteroaryl boronic acids were rapidly, often within minutes, transformed to their corresponding phenols at room temperature. Graphic abstract: [Figure not available: see fulltext.]
- Dutta, Apurba,Ali, Abdul Aziz,Sarma, Diganta
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p. 2379 - 2388
(2019/06/28)
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- Catalyst- And solvent-free: Ipso -hydroxylation of arylboronic acids to phenols
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A catalyst-free method for the hydroxylation of arylboronic acids to form the corresponding phenols with sodium perborate as the oxidant was developed using water as the solvent. Under the reaction conditions, the yield of phenol reached 92% at only 5 min. Moreover, the reaction could be conducted without a catalyst under the solvent-free condition, the efficiency of which was as high as that of a liquid-phase reaction. Using a microcalorimeter, the reaction was found to be an exothermic reaction. The reaction mechanism was investigated and understood via DFT calculations, which revealed that it was a nucleophilic reaction.
- Yang, Xiufang,Jiang, Xulu,Wang, Weitao,Yang, Qi,Ma, Yangmin,Wang, Kuan
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p. 34529 - 34534
(2019/11/13)
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- Trichloroacetonitrile as an efficient activating agent for the: Ipso -hydroxylation of arylboronic acids to phenolic compounds
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A metal-free and base-free Cl3CCN mediated method was developed for the ipso-hydroxylation of aryl boronic acids to their corresponding phenols, which was promoted by a key unstable Lewis adduct intermediate. This transformation has broad functional group tolerance, and late-stage functionalization was successful as well. After simple investigation, two pathways (radical/ionic mechanism) were suggested, and the beneficial action of blue light needs to be further studied.
- Fang, Yuanding,Zhao, Rong,Yao, Yuan,Liu, Yang,Chang, Denghu,Yao, Ming,Shi, Lei
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p. 7558 - 7563
(2019/08/20)
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- Cellulose as recyclable organocatalyst for ipso-hydroxylation of arylboronic acids
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Cellulose catalyzed oxidative hydroxylation of aryl and hetero-arylboronic acids to the corresponding phenols under metal and base free strategy has been demonstrated. The sustainable ipso-hydroxylation takes place using hydrogen peroxide as an oxidant in water under mild condition in shorter period of time. Interestingly, easy recovery and reusability of heterogeneous catalyst without significant loss in catalytic yield makes the protocol environmentally benign.
- Laskar, Khairujjaman,Paul, Subham,Bora, Utpal
-
-
- The highly efficient air oxidation of aryl and alkyl boronic acids by a microwave-assisted protocol under transition metal-free conditions
-
Molecular oxygen is the most important green-oxidant due to its excellent properties. However, the effective utilization of molecular oxygen remains a major challenge in modern chemistry. Herein, we report the development a rapid, green and efficient microwave-assisted protocol for the air oxidation of boronic acids to phenols and alcohols under transition metal-free conditions. In the presence of KOH and DMSO, high yields of the expected phenols and alcohol were obtained with microwave-assistance, and a variety of functional groups were tolerated in this procedure. Notably, this transition metal-free method represents a breakthrough in both organic synthesis and green chemistry for the oxidative hydroxylation of boronic acids to phenols and alcohols.
- Yin, Weiyan,Pan, Xizhi,Leng, Wenxi,Chen, Jian,He, Haifeng
-
supporting information
p. 4614 - 4618
(2019/09/09)
-
- Heterogeneous Palladium–Chitosan–CNT Core–Shell Nanohybrid Composite for Ipso-hydroxylation of Arylboronic Acids
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Abstract: A novel palladium-nanohybrid (Pd–Chitosan–CNT) catalytic composite has been developed using CNT–chitosan nanocomposite and palladium nitrate. The prepared catalytic platform displays excellent catalytic reactivity for the ipso-hydroxylation of various arylboronic acids with a mild oxidant aqueous H2O2 at room temperature, affording the corresponding phenols in excellent yields. Significantly, the easy recovery and reusability by simple manipulation demonstrate the green credentials of this catalytic platform. Graphical Abstract: [Figure not available: see fulltext.]
- Shin, Eun-Jae,Kim, Han-Sem,Joo, Seong-Ryu,Shin, Ueon Sang,Kim, Seung-Hoi
-
-
- Photoinduced hydroxylation of arylboronic acids with molecular oxygen under photocatalyst-free conditions
-
Photoinduced hydroxylation of boronic acids with molecular oxygen under photocatalyst-free conditions is reported, providing a green entry to a variety of phenols and aliphatic alcohols in a highly concise fashion. This new protocol features photocatalyst-free conditions, wide substrate scope and excellent functional group compatibility.
- Xu, Yu-Ting,Li, Chen-Yuan,Huang, Xiao-Bo,Gao, Wen-Xia,Zhou, Yun-Bing,Liu, Miao-Chang,Wu, Hua-Yue
-
supporting information
p. 4971 - 4975
(2019/09/30)
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- Room-Temperature Ionic Liquids (RTILs) as Green Media for Metal- and Base-Free ipso -Hydroxylation of Arylboronic Acids
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The oxidative hydroxylation of arylboronic acids to the corresponding phenolic compounds under metal- and base-free aerobic conditions is successfully demonstrated on a greener media. Hydrogen peroxide, as an eco-friendly oxidant, is compatible with green mediates room-temperature ionic liquids (RTIL)s, providing hydroxylation products of arylboronic acids in an efficient manner. The RTIL support is particularly interesting for its reusability.
- Kim, Seung-Hoi,Kwon, Gyu-Tae,Shin, Eun-Jae
-
supporting information
p. 1815 - 1819
(2019/09/09)
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- A simple, fast and excellent protocol for the synthesis of phenols using CuFe 2O 4 magnetic nanoparticles
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Abstract: This paper describes a very mild, quick and simple protocol for the synthesis of phenols using CuFe 2O 4 magnetic nanoparticles as a catalyst. The nanosized catalyst has an average diameter of 17.63 nm. The magnetic nanoparticles were characterized by SEM, EDX, VSM, XRD and TEM analysis. The synthesis of phenols from phenylboronic acids using H 2O 2 as an oxidant proceeded very well with excellent yields. Heterogeneous catalyst, easy recyclability, mild reaction conditions, short reaction time added as an advantage for the present protocol. Graphical Abstract: A very mild, quick and efficient protocol has been designed for the preparation of phenols from phenyl boronic acids using CuFe 2O 4 Magnetic Nanoparticles (MNPs) as a catalyst. Heterogeneous catalyst, easy recyclability added as an advantage for the protocol.[Figure not available: see fulltext.].
- Chutia, Rituparna,Chetia, Bolin
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- Potassium: Tert -butoxide mediated aerobic hydroxylation of arylboronic acids: An application towards the synthesis of (E)-phenoxy acrylates
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The first example of potassium tert-butoxide mediated aerobic hydroxylation of arylboronic acids is described. A variety of arylboronic acids bearing both electron donating and withdrawing substituents successfully participated in the reaction and furnished phenols in good yields. This strategy also provides access to one pot synthesis of (E)-3-phenoxy acrylates from arylboronic acids and propiolates. The solvent plays an important role and a binary solvent system comprising CH3CN/THF is found to be the best.
- Muhammad, Ibrahim,Balakrishnan, Madasamy Hari,Sasidharan, Manickam,Mannathan, Subramaniyan
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supporting information
p. 11065 - 11068
(2019/07/31)
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- Effect of Co incorporation and support selection on deoxygenation selectivity and stability of (Co)Mo catalysts in anisole HDO
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A series of supported Co modified Mo catalysts was prepared by varying the Co/Mo ratio in the range from 0 to 1 while maintaining the Mo loading at ca. 10 wt%. A sequential incipient wetness impregnation method, with Mo being introduced first, using aqueous solutions of the corresponding precursor salts was employed during the synthesis procedure. Three supports, i.e., Al2O3, ZrO2, and TiO2 differing in textural and acidic properties were investigated. Material physicochemical characteristics were evaluated through ICP-OES, N2-sorption, XRD, H2-TPR, NH3-TPD, O2-TPO, STEM-EDX and XPS techniques. The anisole HDO performance of these CoMo catalysts was evaluated at gas phase conditions in a fixed bed tubular reactor in plug flow regime. The catalysts performance is correlated with properties such as reducibility, acidity, and metal-support interactions. Cobalt addition enhanced the total HDO selectivity by 45% as compared to Mo catalysts. Alumina catalysts displayed higher initial activity (Xanisole≈97%) relative to titania and zirconia supported variants (Xanisole 5+ to be the main active phase while over-reduction to lower Mo states (Mo4+ and Mo3+) as well as carbon deposition are identified as the cause for catalyst activity decrease with TOS.
- Ranga, Chanakya,Alexiadis, Vaios I.,Lauwaert, Jeroen,L?deng, Rune,Thybaut, Joris W.
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- Tetrafluoropyridyl (TFP): a general phenol protecting group readily cleaved under mild conditions
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Phenols are extremely valuable building blocks in the areas of pharmaceuticals, natural products, materials and catalysts. In order to carry out modifications on phenols, the phenolic oxygen is routinely protected to prevent unwanted side reactions. Presently many of the protecting groups available can require harsh conditions, specialist equipment, expensive or air/moisture-sensitive reagents to install and remove. Here we introduce the use of the tetrafluoropyridyl (TFP) group as a general protecting group for phenols. TFP can be installed in one step with no sensitivity to water or air, and it is stable under a range of commonly employed reaction conditions including acid and base. The TFP protecting group is readily cleaved under mild conditions with quantitative conversion to the parent phenol, observed in many cases in less than 1 hour.
- Brittain, William D. G.,Cobb, Steven L.
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supporting information
p. 2110 - 2115
(2019/02/27)
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- Reductive dehalogenation and dehalogenative sulfonation of phenols and heteroaromatics with sodium sulfite in an aqueous medium
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Prototropic tautomerism was used as a tool for the reductive dehalogenation of (hetero)aryl bromides and iodides, or dehalogenative sulfonation of (hetero)aryl chlorides and fluorides, using sodium sulfite as the sole reagent in an aqueous medium. This protocol does not require a metal or phase transfer catalyst and avoids using organic solvent as the reaction medium. This method is especially suitable for substrates that readily tautomerize (such as 2-or 4-halogenated aminophenols and 4-halogenated resorcinols), for which dehalogenation or sulfonation proceeds under mild reaction conditions (≤60 °C). As sodium sulfite is an inexpensive, safe, and environmentally less hazardous reagent, this method has at least three potential applications: (i) in the deprotection of halogens as protecting groups, using sodium sulfite as a reducing agent; (ii) in the sulfonation of aromatic halides under mild reaction conditions avoiding hazardous and corrosive reagents/solvents; and (iii) in the transformation of toxic halogenated aromatics into less harmful compounds.
- Tomanová, Monika,Jedinák, Luká?,Canka?, Petr
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supporting information
p. 2621 - 2628
(2019/06/03)
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